From 4dd4975209f372410c25b26cab0c5f2c513164c3 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 4 Oct 2021 18:23:01 -0400
Subject: [PATCH 01/22] initial parser pass

---
 .../Client/ProjectConfig/Legacy.hs            | 56 +++++++++++++++++--
 1 file changed, 52 insertions(+), 4 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 38852d0fd00..84d6e4455c2 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -43,10 +43,11 @@ import Distribution.Solver.Types.ConstraintSource
 import Distribution.FieldGrammar
 import Distribution.Package
 import Distribution.Types.SourceRepo (RepoType)
+import Distribution.Types.CondTree (CondTree (..), CondBranch (..), condIfThen, condIfThenElse)
 import Distribution.PackageDescription
-         ( dispFlagAssignment )
+         ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment (..) )
 import Distribution.Simple.Compiler
-         ( OptimisationLevel(..), DebugInfoLevel(..) )
+         ( OptimisationLevel(..), DebugInfoLevel(..), CompilerInfo(..) )
 import Distribution.Simple.InstallDirs ( CopyDest (NoCopyDest) )
 import Distribution.Simple.Setup
          ( Flag(Flag), toFlag, fromFlagOrDefault
@@ -92,17 +93,36 @@ import Distribution.Simple.Command
          , OptionField, option, reqArg' )
 import Distribution.Types.PackageVersionConstraint
          ( PackageVersionConstraint )
-import Distribution.Parsec (ParsecParser)
+import Distribution.Parsec (ParsecParser, zeroPos)
+import Distribution.System (Platform (..))
 
 import qualified Data.Map as Map
-import qualified Data.ByteString as BS
+import qualified Data.ByteString.Char8 as BS
 
 import Network.URI (URI (..))
 
+import Distribution.Fields.ConfVar (parseConditionConfVar)
+import qualified Distribution.Fields.ParseResult as FPR
+import Distribution.Fields.Field (SectionArg (..))
+
+
 ------------------------------------------------------------------
 -- Representing the project config file in terms of legacy types
 --
 
+-- ProjectConfigSkeleton is a tree of conditional blocks and imports wrapping a legacy config. It can be finalized by providing the conditional resolution invo
+-- and then resolving and downloading the imports
+
+type ProjectConfigImport = String
+
+type ProjectConfigSkeleton = CondTree ConfVar [ProjectConfigImport] LegacyProjectConfig
+
+finalizeProjectConfigSkeleton :: Platform -> CompilerInfo -> FlagAssignment -> ProjectConfigSkeleton -> IO LegacyProjectConfig
+finalizeProjectConfigSkeleton = undefined
+
+
+
+
 -- | We already have parsers\/pretty-printers for almost all the fields in the
 -- project config file, but they're in terms of the types used for the command
 -- line flags for Setup.hs or cabal commands. We don't want to redefine them
@@ -854,6 +874,34 @@ convertToLegacyPerPackageConfig PackageConfig {..} =
 -- Parsing and showing the project config file
 --
 
+
+parseLegacyProjectSkeleton :: FilePath -> BS.ByteString -> ParseResult ProjectConfigSkeleton
+parseLegacyProjectSkeleton source bs = _ . packResult . mconcat . go $ BS.lines bs
+ where
+  go :: [BS.ByteString] -> [([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
+  go (l:ls)
+       | Just condition <- parseCond l =
+            let (clause, rest) = splitTillIndented ls
+            in case rest of
+                (r:rs) | (BS.pack "else") `BS.isPrefixOf` r -> -- TODO handle elif
+                     let (elseClause, lastRest) = splitTillIndented rs
+                     in ([condIfThenElse condition (clauseToNode clause) (clauseToNode elseClause)], [], []) : go lastRest
+                _ -> ([condIfThen condition (clauseToNode clause)], [], []) : go rest
+       | Just imp <- parseImport l = ([], [imp], []) : go ls
+       | otherwise = ([], [], [l]) : go ls
+  packResult :: ([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree ConfVar [ProjectConfigImport] [BS.ByteString]
+  packResult (branches, imps, ls) = CondNode ls imps branches
+  splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
+  clauseToNode ls = CondNode ls [] [] -- TODO extract imports from lines
+  parseCond :: BS.ByteString -> Maybe (Condition ConfVar)
+  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case FPR.runParseResult (parseConditionConfVar [SecArgOther zeroPos (BS.drop 3 l)]) of -- todo drop end also
+                                                      (_, Left _) -> Nothing
+                                                      (_, Right x) -> Just x
+
+              | otherwise = Nothing
+  parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
+                | otherwise = Nothing
+
 parseLegacyProjectConfig :: FilePath -> BS.ByteString -> ParseResult LegacyProjectConfig
 parseLegacyProjectConfig source =
     parseConfig (legacyProjectConfigFieldDescrs constraintSrc)

From 2ccd991a7fc516b84c6b9cd0d8d61d20d8928a8c Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Thu, 28 Oct 2021 15:13:19 -0400
Subject: [PATCH 02/22] first compiling pass

---
 .../PackageDescription/Configuration.hs       |   1 +
 .../src/Distribution/Client/CmdConfigure.hs   |   3 +-
 .../src/Distribution/Client/CmdOutdated.hs    |   2 +-
 .../src/Distribution/Client/ProjectConfig.hs  |  37 ++---
 .../Client/ProjectConfig/Legacy.hs            | 156 +++++++++++++-----
 .../Distribution/Client/ProjectPlanning.hs    |  73 +++++++-
 .../src/Distribution/Deprecated/ParseUtils.hs |   8 +
 7 files changed, 214 insertions(+), 66 deletions(-)

diff --git a/Cabal/src/Distribution/PackageDescription/Configuration.hs b/Cabal/src/Distribution/PackageDescription/Configuration.hs
index fdb621add6b..e5b40e30189 100644
--- a/Cabal/src/Distribution/PackageDescription/Configuration.hs
+++ b/Cabal/src/Distribution/PackageDescription/Configuration.hs
@@ -32,6 +32,7 @@ module Distribution.PackageDescription.Configuration (
     transformAllBuildInfos,
     transformAllBuildDepends,
     transformAllBuildDependsN,
+    simplifyWithSysParams
   ) where
 
 import Distribution.Compat.Prelude
diff --git a/cabal-install/src/Distribution/Client/CmdConfigure.hs b/cabal-install/src/Distribution/Client/CmdConfigure.hs
index a7a87faab9b..372b8eb1a32 100644
--- a/cabal-install/src/Distribution/Client/CmdConfigure.hs
+++ b/cabal-install/src/Distribution/Client/CmdConfigure.hs
@@ -36,6 +36,7 @@ import Distribution.Client.DistDirLayout
          ( DistDirLayout(..) )
 import Distribution.Client.RebuildMonad (runRebuild)
 import Distribution.Client.ProjectConfig.Types
+import Distribution.Types.CondTree (ignoreConditions)
 
 configureCommand :: CommandUI (NixStyleFlags ())
 configureCommand = CommandUI {
@@ -128,7 +129,7 @@ configureAction' flags@NixStyleFlags {..} _extraArgs globalFlags = do
           then do
             conf <- runRebuild (distProjectRootDirectory . distDirLayout $ baseCtx) $
               readProjectLocalExtraConfig v (distDirLayout baseCtx)
-            return (baseCtx, conf <> cliConfig)
+            return (baseCtx, (fst $ ignoreConditions conf) <> cliConfig) -- TODO ugh. maybe don't have extra configs have conditions, only main configs
           else
             return (baseCtx, cliConfig)
   where
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index b2b817a00ce..f386ff26791 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -302,7 +302,7 @@ depsFromNewFreezeFile verbosity mprojectFile = do
   projectConfig  <- runRebuild (distProjectRootDirectory distDirLayout) $
                     readProjectLocalFreezeConfig verbosity distDirLayout
   let ucnstrs = map fst . projectConfigConstraints . projectConfigShared
-                $ projectConfig
+                $ undefined projectConfig -- TODO instantiate
       deps    = userConstraintsToDependencies ucnstrs
       freezeFile = distProjectFile distDirLayout "freeze"
   freezeFileExists <- doesFileExist freezeFile
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index 17c0435035d..a80205e9c57 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -503,13 +503,13 @@ withProjectOrGlobalConfig' verbosity globalConfigFlag with without = do
 readProjectConfig :: Verbosity
                   -> Flag FilePath
                   -> DistDirLayout
-                  -> Rebuild ProjectConfig
+                  -> Rebuild ProjectConfigSkeleton
 readProjectConfig verbosity configFileFlag distDirLayout = do
     global <- readGlobalConfig                verbosity configFileFlag
     local  <- readProjectLocalConfigOrDefault verbosity distDirLayout
     freeze <- readProjectLocalFreezeConfig    verbosity distDirLayout
     extra  <- readProjectLocalExtraConfig     verbosity distDirLayout
-    return (global <> local <> freeze <> extra)
+    return (singletonProjectConfigSkeleton global <> local <> freeze <> extra)
 
 
 -- | Reads an explicit @cabal.project@ file in the given project root dir,
@@ -517,7 +517,7 @@ readProjectConfig verbosity configFileFlag distDirLayout = do
 --
 readProjectLocalConfigOrDefault :: Verbosity
                                 -> DistDirLayout
-                                -> Rebuild ProjectConfig
+                                -> Rebuild ProjectConfigSkeleton
 readProjectLocalConfigOrDefault verbosity distDirLayout = do
   usesExplicitProjectRoot <- liftIO $ doesFileExist projectFile
   if usesExplicitProjectRoot
@@ -525,7 +525,7 @@ readProjectLocalConfigOrDefault verbosity distDirLayout = do
       readProjectFile verbosity distDirLayout "" "project file"
     else do
       monitorFiles [monitorNonExistentFile projectFile]
-      return defaultImplicitProjectConfig
+      return (singletonProjectConfigSkeleton defaultImplicitProjectConfig)
 
   where
     projectFile = distProjectFile distDirLayout ""
@@ -544,7 +544,7 @@ readProjectLocalConfigOrDefault verbosity distDirLayout = do
 -- principle can be edited manually or by other tools.
 --
 readProjectLocalExtraConfig :: Verbosity -> DistDirLayout
-                            -> Rebuild ProjectConfig
+                            -> Rebuild ProjectConfigSkeleton
 readProjectLocalExtraConfig verbosity distDirLayout =
     readProjectFile verbosity distDirLayout "local"
                              "project local configuration file"
@@ -554,7 +554,7 @@ readProjectLocalExtraConfig verbosity distDirLayout =
 -- principle can be edited manually or by other tools.
 --
 readProjectLocalFreezeConfig :: Verbosity -> DistDirLayout
-                             -> Rebuild ProjectConfig
+                             -> Rebuild ProjectConfigSkeleton
 readProjectLocalFreezeConfig verbosity distDirLayout =
     readProjectFile verbosity distDirLayout "freeze"
                              "project freeze file"
@@ -565,13 +565,14 @@ readProjectFile :: Verbosity
                 -> DistDirLayout
                 -> String
                 -> String
-                -> Rebuild ProjectConfig
+                -> Rebuild ProjectConfigSkeleton
 readProjectFile verbosity DistDirLayout{distProjectFile}
                          extensionName extensionDescription = do
     exists <- liftIO $ doesFileExist extensionFile
     if exists
       then do monitorFiles [monitorFileHashed extensionFile]
-              addProjectFileProvenance <$> liftIO readExtensionFile
+              -- addProjectFileProvenance <$>
+              liftIO readExtensionFile
       else do monitorFiles [monitorNonExistentFile extensionFile]
               return mempty
   where
@@ -579,26 +580,24 @@ readProjectFile verbosity DistDirLayout{distProjectFile}
 
     readExtensionFile =
           reportParseResult verbosity extensionDescription extensionFile
-        . (parseProjectConfig extensionFile)
+      =<< parseProjectSkeleton extensionFile
       =<< BS.readFile extensionFile
-
+{-
     addProjectFileProvenance config =
       config {
-        projectConfigProvenance =
-          Set.insert (Explicit extensionFile) (projectConfigProvenance config)
+        projectConfigProvenance = _ config
+          -- Set.insert (Explicit extensionFile) (projectConfigProvenance config)
       }
-
-
+-}
+{-
 -- | Parse the 'ProjectConfig' format.
 --
 -- For the moment this is implemented in terms of parsers for legacy
 -- configuration types, plus a conversion.
 --
-parseProjectConfig :: FilePath -> BS.ByteString -> OldParser.ParseResult ProjectConfig
-parseProjectConfig source content =
-    convertLegacyProjectConfig <$>
-      (parseLegacyProjectConfig source content)
-
+parseProjectConfigSkeleton :: FilePath -> BS.ByteString -> IO (OldParser.ParseResult ProjectConfigSkeleton)
+parseProjectConfigSkeleton source content = (parseProjectSkeleton source content)
+-}
 
 -- | Render the 'ProjectConfig' format.
 --
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 84d6e4455c2..77179f499b9 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -1,9 +1,15 @@
-{-# LANGUAGE RecordWildCards, NamedFieldPuns, DeriveGeneric, ConstraintKinds #-}
+{-# LANGUAGE RecordWildCards, NamedFieldPuns, DeriveGeneric, ConstraintKinds, FlexibleInstances #-}
 
 -- | Project configuration, implementation in terms of legacy types.
 --
 module Distribution.Client.ProjectConfig.Legacy (
 
+   -- Project config skeletons
+    ProjectConfigSkeleton,
+    parseProjectSkeleton,
+    instantiateProjectConfigSkeleton,
+    singletonProjectConfigSkeleton,
+
     -- * Project config in terms of legacy types
     LegacyProjectConfig,
     parseLegacyProjectConfig,
@@ -17,13 +23,12 @@ module Distribution.Client.ProjectConfig.Legacy (
 
     -- * Internals, just for tests
     parsePackageLocationTokenQ,
-    renderPackageLocationToken,
+    renderPackageLocationToken
   ) where
 
-import Prelude ()
 import Distribution.Client.Compat.Prelude
 
-import Distribution.Types.Flag (parsecFlagAssignment)
+import Distribution.Types.Flag (parsecFlagAssignment, FlagName)
 
 import Distribution.Client.ProjectConfig.Types
 import Distribution.Client.Types.RepoName (RepoName (..), unRepoName)
@@ -43,9 +48,10 @@ import Distribution.Solver.Types.ConstraintSource
 import Distribution.FieldGrammar
 import Distribution.Package
 import Distribution.Types.SourceRepo (RepoType)
-import Distribution.Types.CondTree (CondTree (..), CondBranch (..), condIfThen, condIfThenElse)
+import Distribution.Types.CondTree (CondTree (..), CondBranch (..), condIfThen, condIfThenElse, mapTreeConds)
 import Distribution.PackageDescription
          ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment (..) )
+import Distribution.PackageDescription.Configuration (simplifyWithSysParams)
 import Distribution.Simple.Compiler
          ( OptimisationLevel(..), DebugInfoLevel(..), CompilerInfo(..) )
 import Distribution.Simple.InstallDirs ( CopyDest (NoCopyDest) )
@@ -94,9 +100,10 @@ import Distribution.Simple.Command
 import Distribution.Types.PackageVersionConstraint
          ( PackageVersionConstraint )
 import Distribution.Parsec (ParsecParser, zeroPos)
-import Distribution.System (Platform (..))
+import Distribution.System (Platform (..), OS, Arch)
 
 import qualified Data.Map as Map
+import qualified Data.Set as Set
 import qualified Data.ByteString.Char8 as BS
 
 import Network.URI (URI (..))
@@ -107,21 +114,119 @@ import Distribution.Fields.Field (SectionArg (..))
 
 
 ------------------------------------------------------------------
--- Representing the project config file in terms of legacy types
+-- Handle extended project config files with conditionals and imports.
 --
 
--- ProjectConfigSkeleton is a tree of conditional blocks and imports wrapping a legacy config. It can be finalized by providing the conditional resolution invo
+-- | ProjectConfigSkeleton is a tree of conditional blocks and imports wrapping a config. It can be finalized by providing the conditional resolution info
 -- and then resolving and downloading the imports
-
+type ProjectConfigSkeleton = CondTree ConfVar [ProjectConfigImport] ProjectConfig
 type ProjectConfigImport = String
 
-type ProjectConfigSkeleton = CondTree ConfVar [ProjectConfigImport] LegacyProjectConfig
 
-finalizeProjectConfigSkeleton :: Platform -> CompilerInfo -> FlagAssignment -> ProjectConfigSkeleton -> IO LegacyProjectConfig
-finalizeProjectConfigSkeleton = undefined
+instance Semigroup (CondTree ConfVar [ProjectConfigImport] ProjectConfig) where
+  (CondNode a c bs) <> (CondNode a' c' bs') = CondNode (a <> a') (c <> c') (bs <> bs')
+
+instance Monoid (CondTree ConfVar [ProjectConfigImport] ProjectConfig) where
+   mappend = (<>)
+   mempty = CondNode mempty mempty mempty
+
+singletonProjectConfigSkeleton :: ProjectConfig -> ProjectConfigSkeleton
+singletonProjectConfigSkeleton x = CondNode x mempty mempty
+
+instantiateProjectConfigSkeleton :: OS -> Arch -> CompilerInfo -> FlagAssignment -> ProjectConfigSkeleton -> ProjectConfig
+instantiateProjectConfigSkeleton os arch impl flags skel = go $ mapTreeConds (fst . simplifyWithSysParams os arch impl) skel -- TODO bail on flags
+    where
+        go :: CondTree
+               FlagName
+               [ProjectConfigImport]
+               ProjectConfig
+             -> ProjectConfig
+        go (CondNode l _imps ts) =
+           let branches = concatMap processBranch ts
+           in l <> mconcat branches
+        processBranch (CondBranch cnd t mf) = case cnd of
+           (Lit True) ->  [go t]
+           (Lit False) -> maybe ([]) ((:[]) . go) mf
+           _ -> []
+
+{-
+
+   where
+        go :: CondTree
+               FlagName
+               [ProjectConfigImport]
+               ProjectConfig
+             -> IO (ParseResult ProjectConfig)
+        go (CondNode l imps ts) = do
+           -- ugly code to avoid defining legacy parse results explicitly as a monad transformer. shrug.
+           impSkel <- sequenceA <$> mapM readImportConfig imps
+           impConfig <-  fmap (fmap mconcat) . fmap (join . fmap sequenceA) . sequenceA $ fmap (mapM (instantiateProjectConfigSkeleton os arch impl flags)) impSkel
+           branches <- mconcatParse . concat <$> mapM processBranch ts
+           pure $ mconcatParse [pure l, impConfig, branches]
+        processBranch (CondBranch cnd t mf) = case cnd of
+           (Lit True) -> (:[]) <$> go t
+           (Lit False) -> maybe (pure []) (fmap (:[]) . go) mf
+           _ -> pure []
+        mconcatParse = fmap mconcat . sequenceA
+-}
+
+-- TODO ensure parse doesn't have flags setting compiler inside conditionals
+parseProjectSkeleton :: FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
+parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
+ where
+  linesToNode :: [BS.ByteString] -> IO (CondTree ConfVar [ProjectConfigImport] [BS.ByteString])
+  linesToNode ls = packResult . mconcat <$> go ls
+
+  packResult :: ([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree ConfVar [ProjectConfigImport] [BS.ByteString]
+  packResult (branches, imps, ls) = CondNode ls imps branches
+
+  go :: [BS.ByteString] -> IO [([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
+  go (l:ls)
+       | Just condition <- parseCond l =
+            let (clause, rest) = splitTillIndented ls
+            in case rest of
+                (r:rs) | (BS.pack "else") `BS.isPrefixOf` r -> -- TODO handle elif
+                     let (elseClause, lastRest) = splitTillIndented rs
+                     in do
+                        c1 <- linesToNode clause
+                        c2 <- linesToNode elseClause
+                        (([condIfThenElse condition c1 c2], [], []) :) <$> go lastRest
+                _ -> do
+                     c1 <- linesToNode clause
+                     (([condIfThen condition c1], [], []) :) <$>  go rest
+       | Just imp <- parseImport l = do x <- go . BS.lines =<< fetchImportConfig imp
+                                        ((([], [imp], []) : x) ++) <$> go ls
+       | otherwise = (([], [], [l]) :) <$> go ls
+  go [] = pure []
+
+  splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
+
+  parseCond :: BS.ByteString -> Maybe (Condition ConfVar)
+  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case FPR.runParseResult (parseConditionConfVar [SecArgOther zeroPos (BS.takeWhile (/=')') $ BS.drop 3 l)]) of
+                                                      (_, Left _) -> Nothing
+                                                      (_, Right x) -> Just x
+
+              | otherwise = Nothing
+  parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
+                | otherwise = Nothing
+  runInnerParsers :: CondTree ConfVar [ProjectConfigImport] [BS.ByteString] -> ParseResult ProjectConfigSkeleton
+  runInnerParsers = traverse (fmap (addProvenance . convertLegacyProjectConfig) . parseLegacyProjectConfig source . BS.unlines)
+
+  addProvenance x = x {projectConfigProvenance = Set.singleton (Explicit source)}
 
+  fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
+  fetchImportConfig = BS.readFile -- todo, handle http
 
+{-
+-- todo handlehttp
+readImportConfig :: ProjectConfigImport -> IO (ParseResult ProjectConfigSkeleton)
+readImportConfig x = parseProjectSkeleton x <$> BS.readFile x
+-- todo add extra files to file change monitor
+-}
 
+------------------------------------------------------------------
+-- Representing the project config file in terms of legacy types
+--
 
 -- | We already have parsers\/pretty-printers for almost all the fields in the
 -- project config file, but they're in terms of the types used for the command
@@ -875,33 +980,6 @@ convertToLegacyPerPackageConfig PackageConfig {..} =
 --
 
 
-parseLegacyProjectSkeleton :: FilePath -> BS.ByteString -> ParseResult ProjectConfigSkeleton
-parseLegacyProjectSkeleton source bs = _ . packResult . mconcat . go $ BS.lines bs
- where
-  go :: [BS.ByteString] -> [([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
-  go (l:ls)
-       | Just condition <- parseCond l =
-            let (clause, rest) = splitTillIndented ls
-            in case rest of
-                (r:rs) | (BS.pack "else") `BS.isPrefixOf` r -> -- TODO handle elif
-                     let (elseClause, lastRest) = splitTillIndented rs
-                     in ([condIfThenElse condition (clauseToNode clause) (clauseToNode elseClause)], [], []) : go lastRest
-                _ -> ([condIfThen condition (clauseToNode clause)], [], []) : go rest
-       | Just imp <- parseImport l = ([], [imp], []) : go ls
-       | otherwise = ([], [], [l]) : go ls
-  packResult :: ([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree ConfVar [ProjectConfigImport] [BS.ByteString]
-  packResult (branches, imps, ls) = CondNode ls imps branches
-  splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
-  clauseToNode ls = CondNode ls [] [] -- TODO extract imports from lines
-  parseCond :: BS.ByteString -> Maybe (Condition ConfVar)
-  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case FPR.runParseResult (parseConditionConfVar [SecArgOther zeroPos (BS.drop 3 l)]) of -- todo drop end also
-                                                      (_, Left _) -> Nothing
-                                                      (_, Right x) -> Just x
-
-              | otherwise = Nothing
-  parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
-                | otherwise = Nothing
-
 parseLegacyProjectConfig :: FilePath -> BS.ByteString -> ParseResult LegacyProjectConfig
 parseLegacyProjectConfig source =
     parseConfig (legacyProjectConfigFieldDescrs constraintSrc)
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index b166c03cbb8..d37d9a4563d 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -76,6 +76,7 @@ import           Distribution.Client.PackageHash
 import           Distribution.Client.RebuildMonad
 import           Distribution.Client.Store
 import           Distribution.Client.ProjectConfig
+import           Distribution.Client.ProjectConfig.Legacy
 import           Distribution.Client.ProjectPlanOutput
 
 import           Distribution.Client.Types
@@ -322,10 +323,12 @@ rebuildProjectConfig verbosity
       runRebuild distProjectRootDirectory
       $ rerunIfChanged verbosity
                        fileMonitorProjectConfig
-                       fileMonitorProjectConfigKey
+                       fileMonitorProjectConfigKey -- todo check deps too?
       $ do
           liftIO $ info verbosity "Project settings changed, reconfiguring..."
-          projectConfig <- phaseReadProjectConfig
+          projectConfigSkeleton <- phaseReadProjectConfig -- ignoreConditions
+          (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout (fst $ PD.ignoreConditions projectConfigSkeleton)
+          let projectConfig = instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty projectConfigSkeleton
           localPackages <- phaseReadLocalPackages projectConfig
           return (projectConfig, localPackages)
 
@@ -353,7 +356,7 @@ rebuildProjectConfig verbosity
     -- Read the cabal.project (or implicit config) and combine it with
     -- arguments from the command line
     --
-    phaseReadProjectConfig :: Rebuild ProjectConfig
+    phaseReadProjectConfig :: Rebuild ProjectConfigSkeleton
     phaseReadProjectConfig = do
       readProjectConfig verbosity projectConfigConfigFile distDirLayout
 
@@ -380,6 +383,63 @@ rebuildProjectConfig verbosity
                                  pkgLocations
 
 
+configureCompiler :: Verbosity ->
+                     DistDirLayout ->
+                     ProjectConfig ->
+                     Rebuild (Compiler, Platform, ProgramDb)
+configureCompiler verbosity
+                  DistDirLayout {
+                     distProjectCacheFile
+                   }
+                  ProjectConfig {
+                             projectConfigShared = ProjectConfigShared {
+                               projectConfigHcFlavor,
+                               projectConfigHcPath,
+                               projectConfigHcPkg
+                             },
+                             projectConfigLocalPackages = PackageConfig {
+                               packageConfigProgramPaths,
+                               packageConfigProgramArgs,
+                               packageConfigProgramPathExtra
+                             }
+                           } = do
+        let fileMonitorCompiler       = newFileMonitor . distProjectCacheFile $ "compiler"
+
+        progsearchpath <- liftIO $ getSystemSearchPath
+        rerunIfChanged verbosity fileMonitorCompiler
+                       (hcFlavor, hcPath, hcPkg, progsearchpath,
+                        packageConfigProgramPaths,
+                        packageConfigProgramArgs,
+                        packageConfigProgramPathExtra) $ do
+
+          liftIO $ info verbosity "Compiler settings changed, reconfiguring..."
+          result@(_, _, progdb') <- liftIO $
+            Cabal.configCompilerEx
+              hcFlavor hcPath hcPkg
+              progdb verbosity
+
+        -- Note that we added the user-supplied program locations and args
+        -- for /all/ programs, not just those for the compiler prog and
+        -- compiler-related utils. In principle we don't know which programs
+        -- the compiler will configure (and it does vary between compilers).
+        -- We do know however that the compiler will only configure the
+        -- programs it cares about, and those are the ones we monitor here.
+          monitorFiles (programsMonitorFiles progdb')
+
+          return result
+      where
+        hcFlavor = flagToMaybe projectConfigHcFlavor
+        hcPath   = flagToMaybe projectConfigHcPath
+        hcPkg    = flagToMaybe projectConfigHcPkg
+        progdb   =
+            userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths))
+          . userSpecifyArgss (Map.toList (getMapMappend packageConfigProgramArgs))
+          . modifyProgramSearchPath
+              (++ [ ProgramSearchPathDir dir
+                  | dir <- fromNubList packageConfigProgramPathExtra ])
+          $ defaultProgramDb
+
+
 -- | Return an up-to-date elaborated install plan.
 --
 -- Two variants of the install plan are returned: with and without packages
@@ -451,7 +511,6 @@ rebuildInstallPlan verbosity
       return (improvedPlan, elaboratedPlan, elaboratedShared, totalIndexState, activeRepos)
 
   where
-    fileMonitorCompiler       = newFileMonitorInCacheDir "compiler"
     fileMonitorSolverPlan     = newFileMonitorInCacheDir "solver-plan"
     fileMonitorSourceHashes   = newFileMonitorInCacheDir "source-hashes"
     fileMonitorElaboratedPlan = newFileMonitorInCacheDir "elaborated-plan"
@@ -468,7 +527,9 @@ rebuildInstallPlan verbosity
     --
     phaseConfigureCompiler :: ProjectConfig
                            -> Rebuild (Compiler, Platform, ProgramDb)
-    phaseConfigureCompiler ProjectConfig {
+    phaseConfigureCompiler = configureCompiler verbosity distDirLayout
+{-
+    ProjectConfig {
                              projectConfigShared = ProjectConfigShared {
                                projectConfigHcFlavor,
                                projectConfigHcPath,
@@ -513,7 +574,7 @@ rebuildInstallPlan verbosity
               (++ [ ProgramSearchPathDir dir
                   | dir <- fromNubList packageConfigProgramPathExtra ])
           $ defaultProgramDb
-
+-}
 
     -- Configuring other programs.
     --
diff --git a/cabal-install/src/Distribution/Deprecated/ParseUtils.hs b/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
index 78f57b58d78..c1a0e4cd30c 100644
--- a/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
+++ b/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
@@ -106,6 +106,14 @@ instance Monad ParseResult where
                                ParseFailed err -> ParseFailed err
                                ParseOk ws' x' -> ParseOk (ws'++ws) x'
 
+instance Foldable ParseResult where
+  foldMap _ (ParseFailed _ ) = mempty
+  foldMap f (ParseOk _ x) = f x
+
+instance Traversable ParseResult where
+  traverse _ (ParseFailed err) = pure (ParseFailed err)
+  traverse f (ParseOk ws x) = ParseOk ws <$> f x
+
 #if !(MIN_VERSION_base(4,9,0))
         fail = parseResultFail
 #elif !(MIN_VERSION_base(4,13,0))

From e807d2db0079e9b111ee583989a2313e4c471f37 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 29 Nov 2021 18:29:35 -0500
Subject: [PATCH 03/22] get more stuff sort of working

---
 .../src/Distribution/Client/CmdConfigure.hs   |  1 -
 .../src/Distribution/Client/CmdOutdated.hs    |  2 +-
 .../src/Distribution/Client/ProjectConfig.hs  | 60 ++++++++++++-------
 .../Client/ProjectConfig/Legacy.hs            | 21 -------
 .../Distribution/Client/ProjectPlanning.hs    |  4 +-
 5 files changed, 41 insertions(+), 47 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/CmdConfigure.hs b/cabal-install/src/Distribution/Client/CmdConfigure.hs
index 372b8eb1a32..dd30de8af2b 100644
--- a/cabal-install/src/Distribution/Client/CmdConfigure.hs
+++ b/cabal-install/src/Distribution/Client/CmdConfigure.hs
@@ -36,7 +36,6 @@ import Distribution.Client.DistDirLayout
          ( DistDirLayout(..) )
 import Distribution.Client.RebuildMonad (runRebuild)
 import Distribution.Client.ProjectConfig.Types
-import Distribution.Types.CondTree (ignoreConditions)
 
 configureCommand :: CommandUI (NixStyleFlags ())
 configureCommand = CommandUI {
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index f386ff26791..b2b817a00ce 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -302,7 +302,7 @@ depsFromNewFreezeFile verbosity mprojectFile = do
   projectConfig  <- runRebuild (distProjectRootDirectory distDirLayout) $
                     readProjectLocalFreezeConfig verbosity distDirLayout
   let ucnstrs = map fst . projectConfigConstraints . projectConfigShared
-                $ undefined projectConfig -- TODO instantiate
+                $ projectConfig
       deps    = userConstraintsToDependencies ucnstrs
       freezeFile = distProjectFile distDirLayout "freeze"
   freezeFileExists <- doesFileExist freezeFile
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index a80205e9c57..2c21a11708e 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -505,11 +505,11 @@ readProjectConfig :: Verbosity
                   -> DistDirLayout
                   -> Rebuild ProjectConfigSkeleton
 readProjectConfig verbosity configFileFlag distDirLayout = do
-    global <- readGlobalConfig                verbosity configFileFlag
+    global <- singletonProjectConfigSkeleton <$> readGlobalConfig                verbosity configFileFlag
     local  <- readProjectLocalConfigOrDefault verbosity distDirLayout
-    freeze <- readProjectLocalFreezeConfig    verbosity distDirLayout
-    extra  <- readProjectLocalExtraConfig     verbosity distDirLayout
-    return (singletonProjectConfigSkeleton global <> local <> freeze <> extra)
+    freeze <- singletonProjectConfigSkeleton <$> readProjectLocalFreezeConfig    verbosity distDirLayout
+    extra  <- singletonProjectConfigSkeleton <$> readProjectLocalExtraConfig     verbosity distDirLayout
+    return (global <> local <> freeze <> extra)
 
 
 -- | Reads an explicit @cabal.project@ file in the given project root dir,
@@ -522,7 +522,7 @@ readProjectLocalConfigOrDefault verbosity distDirLayout = do
   usesExplicitProjectRoot <- liftIO $ doesFileExist projectFile
   if usesExplicitProjectRoot
     then do
-      readProjectFile verbosity distDirLayout "" "project file"
+      readProjectFileSkeleton verbosity distDirLayout "" "project file"
     else do
       monitorFiles [monitorNonExistentFile projectFile]
       return (singletonProjectConfigSkeleton defaultImplicitProjectConfig)
@@ -544,7 +544,7 @@ readProjectLocalConfigOrDefault verbosity distDirLayout = do
 -- principle can be edited manually or by other tools.
 --
 readProjectLocalExtraConfig :: Verbosity -> DistDirLayout
-                            -> Rebuild ProjectConfigSkeleton
+                            -> Rebuild ProjectConfig
 readProjectLocalExtraConfig verbosity distDirLayout =
     readProjectFile verbosity distDirLayout "local"
                              "project local configuration file"
@@ -554,24 +554,19 @@ readProjectLocalExtraConfig verbosity distDirLayout =
 -- principle can be edited manually or by other tools.
 --
 readProjectLocalFreezeConfig :: Verbosity -> DistDirLayout
-                             -> Rebuild ProjectConfigSkeleton
+                             -> Rebuild ProjectConfig
 readProjectLocalFreezeConfig verbosity distDirLayout =
     readProjectFile verbosity distDirLayout "freeze"
                              "project freeze file"
 
--- | Reads a named config file in the given project root dir, or returns empty.
+-- | Reads a named extended (with imports and conditionals) config file in the given project root dir, or returns empty.
 --
-readProjectFile :: Verbosity
-                -> DistDirLayout
-                -> String
-                -> String
-                -> Rebuild ProjectConfigSkeleton
-readProjectFile verbosity DistDirLayout{distProjectFile}
+readProjectFileSkeleton :: Verbosity -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeleton verbosity DistDirLayout{distProjectFile}
                          extensionName extensionDescription = do
     exists <- liftIO $ doesFileExist extensionFile
     if exists
       then do monitorFiles [monitorFileHashed extensionFile]
-              -- addProjectFileProvenance <$>
               liftIO readExtensionFile
       else do monitorFiles [monitorNonExistentFile extensionFile]
               return mempty
@@ -582,22 +577,41 @@ readProjectFile verbosity DistDirLayout{distProjectFile}
           reportParseResult verbosity extensionDescription extensionFile
       =<< parseProjectSkeleton extensionFile
       =<< BS.readFile extensionFile
-{-
+
+-- | Reads a named config file in the given project root dir, or returns empty.
+--
+readProjectFile :: Verbosity -> DistDirLayout -> String -> String -> Rebuild ProjectConfig
+readProjectFile verbosity DistDirLayout{distProjectFile}
+                         extensionName extensionDescription = do
+    exists <- liftIO $ doesFileExist extensionFile
+    if exists
+      then do monitorFiles [monitorFileHashed extensionFile]
+              addProjectFileProvenance <$> liftIO readExtensionFile
+      else do monitorFiles [monitorNonExistentFile extensionFile]
+              return mempty
+  where
+    extensionFile = distProjectFile extensionName
+
+    readExtensionFile =
+          reportParseResult verbosity extensionDescription extensionFile
+        . (parseProjectConfig extensionFile)
+      =<< BS.readFile extensionFile
+
     addProjectFileProvenance config =
       config {
-        projectConfigProvenance = _ config
-          -- Set.insert (Explicit extensionFile) (projectConfigProvenance config)
+        projectConfigProvenance = Set.insert (Explicit extensionFile) (projectConfigProvenance config)
       }
--}
-{-
+
+
 -- | Parse the 'ProjectConfig' format.
 --
 -- For the moment this is implemented in terms of parsers for legacy
 -- configuration types, plus a conversion.
 --
-parseProjectConfigSkeleton :: FilePath -> BS.ByteString -> IO (OldParser.ParseResult ProjectConfigSkeleton)
-parseProjectConfigSkeleton source content = (parseProjectSkeleton source content)
--}
+parseProjectConfig :: FilePath -> BS.ByteString -> OldParser.ParseResult ProjectConfig
+parseProjectConfig source content =
+    convertLegacyProjectConfig <$>
+      (parseLegacyProjectConfig source content)
 
 -- | Render the 'ProjectConfig' format.
 --
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 77179f499b9..747fe409abd 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -149,27 +149,6 @@ instantiateProjectConfigSkeleton os arch impl flags skel = go $ mapTreeConds (fs
            (Lit False) -> maybe ([]) ((:[]) . go) mf
            _ -> []
 
-{-
-
-   where
-        go :: CondTree
-               FlagName
-               [ProjectConfigImport]
-               ProjectConfig
-             -> IO (ParseResult ProjectConfig)
-        go (CondNode l imps ts) = do
-           -- ugly code to avoid defining legacy parse results explicitly as a monad transformer. shrug.
-           impSkel <- sequenceA <$> mapM readImportConfig imps
-           impConfig <-  fmap (fmap mconcat) . fmap (join . fmap sequenceA) . sequenceA $ fmap (mapM (instantiateProjectConfigSkeleton os arch impl flags)) impSkel
-           branches <- mconcatParse . concat <$> mapM processBranch ts
-           pure $ mconcatParse [pure l, impConfig, branches]
-        processBranch (CondBranch cnd t mf) = case cnd of
-           (Lit True) -> (:[]) <$> go t
-           (Lit False) -> maybe (pure []) (fmap (:[]) . go) mf
-           _ -> pure []
-        mconcatParse = fmap mconcat . sequenceA
--}
-
 -- TODO ensure parse doesn't have flags setting compiler inside conditionals
 parseProjectSkeleton :: FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
 parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index d37d9a4563d..b555605fad9 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -326,7 +326,9 @@ rebuildProjectConfig verbosity
                        fileMonitorProjectConfigKey -- todo check deps too?
       $ do
           liftIO $ info verbosity "Project settings changed, reconfiguring..."
-          projectConfigSkeleton <- phaseReadProjectConfig -- ignoreConditions
+          liftIO $ createDirectoryIfMissingVerbose verbosity True distProjectCacheDirectory
+          projectConfigSkeleton <- phaseReadProjectConfig
+          -- have to create the cache directory before configuring the compiler
           (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout (fst $ PD.ignoreConditions projectConfigSkeleton)
           let projectConfig = instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty projectConfigSkeleton
           localPackages <- phaseReadLocalPackages projectConfig

From ca7499a3b7af597c550108d6fb8b0067d97b461f Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 29 Nov 2021 20:55:33 -0500
Subject: [PATCH 04/22] conditional parsing actually works

---
 Cabal/src/Distribution/Fields/ConfVar.hs      | 11 +++++++++--
 .../src/Distribution/Client/CmdConfigure.hs   |  2 +-
 .../Client/ProjectConfig/Legacy.hs            | 19 +++++++++++++------
 3 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/Cabal/src/Distribution/Fields/ConfVar.hs b/Cabal/src/Distribution/Fields/ConfVar.hs
index 68601cd53e9..533dfd5e824 100644
--- a/Cabal/src/Distribution/Fields/ConfVar.hs
+++ b/Cabal/src/Distribution/Fields/ConfVar.hs
@@ -1,14 +1,15 @@
 {-# LANGUAGE OverloadedStrings #-}
-module Distribution.Fields.ConfVar (parseConditionConfVar) where
+module Distribution.Fields.ConfVar (parseConditionConfVar, parseConditionConfVarFromClause) where
 
 import Distribution.Compat.CharParsing     (char, integral)
 import Distribution.Compat.Prelude
-import Distribution.Fields.Field           (SectionArg (..))
+import Distribution.Fields.Field           (SectionArg (..), Field(..))
 import Distribution.Fields.ParseResult
 import Distribution.Parsec                 (Parsec (..), Position (..), runParsecParser)
 import Distribution.Parsec.FieldLineStream (fieldLineStreamFromBS)
 import Distribution.Types.Condition
 import Distribution.Types.ConfVar          (ConfVar (..))
+import Distribution.Fields.Parser          (readFields)
 import Distribution.Version
        (anyVersion, earlierVersion, intersectVersionRanges, laterVersion, majorBoundVersion,
        mkVersion, noVersion, orEarlierVersion, orLaterVersion, thisVersion, unionVersionRanges,
@@ -17,6 +18,12 @@ import Prelude ()
 
 import qualified Text.Parsec       as P
 import qualified Text.Parsec.Error as P
+import qualified Data.ByteString.Char8          as B8
+
+parseConditionConfVarFromClause :: B8.ByteString -> Either P.ParseError (Condition ConfVar)
+parseConditionConfVarFromClause x = readFields x >>= \r -> case r of
+                                       (Section _ xs _ : _ ) -> P.runParser (parser <* P.eof) () "<condition>" xs
+                                       _ -> error "guh"
 
 -- | Parse @'Condition' 'ConfVar'@ from section arguments provided by parsec
 -- based outline parser.
diff --git a/cabal-install/src/Distribution/Client/CmdConfigure.hs b/cabal-install/src/Distribution/Client/CmdConfigure.hs
index dd30de8af2b..f734f15c668 100644
--- a/cabal-install/src/Distribution/Client/CmdConfigure.hs
+++ b/cabal-install/src/Distribution/Client/CmdConfigure.hs
@@ -128,7 +128,7 @@ configureAction' flags@NixStyleFlags {..} _extraArgs globalFlags = do
           then do
             conf <- runRebuild (distProjectRootDirectory . distDirLayout $ baseCtx) $
               readProjectLocalExtraConfig v (distDirLayout baseCtx)
-            return (baseCtx, (fst $ ignoreConditions conf) <> cliConfig) -- TODO ugh. maybe don't have extra configs have conditions, only main configs
+            return (baseCtx, conf <> cliConfig) -- TODO ugh. maybe don't have extra configs have conditions, only main configs
           else
             return (baseCtx, cliConfig)
   where
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 747fe409abd..5379d877c43 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -108,11 +108,13 @@ import qualified Data.ByteString.Char8 as BS
 
 import Network.URI (URI (..))
 
-import Distribution.Fields.ConfVar (parseConditionConfVar)
+import Distribution.Fields.ConfVar (parseConditionConfVarFromClause)
 import qualified Distribution.Fields.ParseResult as FPR
 import Distribution.Fields.Field (SectionArg (..))
 
 
+
+
 ------------------------------------------------------------------
 -- Handle extended project config files with conditionals and imports.
 --
@@ -149,7 +151,10 @@ instantiateProjectConfigSkeleton os arch impl flags skel = go $ mapTreeConds (fs
            (Lit False) -> maybe ([]) ((:[]) . go) mf
            _ -> []
 
+
 -- TODO ensure parse doesn't have flags setting compiler inside conditionals
+
+-- NOTE a nice refactor would be to use readFields directly to get a tree structure.
 parseProjectSkeleton :: FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
 parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
  where
@@ -181,9 +186,9 @@ parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
   splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
 
   parseCond :: BS.ByteString -> Maybe (Condition ConfVar)
-  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case FPR.runParseResult (parseConditionConfVar [SecArgOther zeroPos (BS.takeWhile (/=')') $ BS.drop 3 l)]) of
-                                                      (_, Left _) -> Nothing
-                                                      (_, Right x) -> Just x
+  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case parseConditionConfVarFromClause l of
+                                                      Left err -> error (show err) -- TODO improve error reporting here
+                                                      Right x -> Just x
 
               | otherwise = Nothing
   parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
@@ -198,9 +203,11 @@ parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
 
 {-
 -- todo handlehttp
-readImportConfig :: ProjectConfigImport -> IO (ParseResult ProjectConfigSkeleton)
-readImportConfig x = parseProjectSkeleton x <$> BS.readFile x
 -- todo add extra files to file change monitor
+
+-- TODO handle importing legacy freeze as well
+-- TODO handle merge semantics for constraints specially
+
 -}
 
 ------------------------------------------------------------------

From 0c6e6e326c9924bc9ef254a3820bf4a2aeb31fd6 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 3 Jan 2022 15:08:04 -0500
Subject: [PATCH 05/22] error cleanup and downloads

---
 Cabal/src/Distribution/Fields/ConfVar.hs      |  3 +-
 Cabal/src/Distribution/Types/CondTree.hs      |  9 +-
 .../Client/ProjectConfig/Legacy.hs            | 93 ++++++++++++-------
 3 files changed, 68 insertions(+), 37 deletions(-)

diff --git a/Cabal/src/Distribution/Fields/ConfVar.hs b/Cabal/src/Distribution/Fields/ConfVar.hs
index 533dfd5e824..b045c3ef172 100644
--- a/Cabal/src/Distribution/Fields/ConfVar.hs
+++ b/Cabal/src/Distribution/Fields/ConfVar.hs
@@ -17,13 +17,14 @@ import Distribution.Version
 import Prelude ()
 
 import qualified Text.Parsec       as P
+import qualified Text.Parsec.Pos   as P
 import qualified Text.Parsec.Error as P
 import qualified Data.ByteString.Char8          as B8
 
 parseConditionConfVarFromClause :: B8.ByteString -> Either P.ParseError (Condition ConfVar)
 parseConditionConfVarFromClause x = readFields x >>= \r -> case r of
                                        (Section _ xs _ : _ ) -> P.runParser (parser <* P.eof) () "<condition>" xs
-                                       _ -> error "guh"
+                                       _ -> Left $ P.newErrorMessage (P.Message "No fields in clause") (P.initialPos "<condition>")
 
 -- | Parse @'Condition' 'ConfVar'@ from section arguments provided by parsec
 -- based outline parser.
diff --git a/Cabal/src/Distribution/Types/CondTree.hs b/Cabal/src/Distribution/Types/CondTree.hs
index 8fd233658f5..442e4b48b8c 100644
--- a/Cabal/src/Distribution/Types/CondTree.hs
+++ b/Cabal/src/Distribution/Types/CondTree.hs
@@ -68,6 +68,13 @@ instance (Binary v, Binary c, Binary a) => Binary (CondTree v c a)
 instance (Structured v, Structured c, Structured a) => Structured (CondTree v c a)
 instance (NFData v, NFData c, NFData a) => NFData (CondTree v c a) where rnf = genericRnf
 
+instance (Semigroup a, Semigroup c) => Semigroup (CondTree v c a) where
+  (CondNode a c bs) <> (CondNode a' c' bs') = CondNode (a <> a') (c <> c') (bs <> bs')
+
+instance (Monoid a, Monoid c) => Monoid (CondTree v c a) where
+   mappend = (<>)
+   mempty = CondNode mempty mempty mempty
+
 -- | A 'CondBranch' represents a conditional branch, e.g., @if
 -- flag(foo)@ on some syntax @a@.  It also has an optional false
 -- branch.
@@ -191,4 +198,4 @@ foldCondTree e u mergeInclusive mergeExclusive = goTree
     goTree :: CondTree v c a -> b
     goTree (CondNode a c ifs) = u (c, a) `mergeInclusive` foldl goBranch e ifs
     goBranch :: b -> CondBranch v c a -> b
-    goBranch acc (CondBranch _ t mt) = mergeInclusive acc (maybe (goTree t) (mergeExclusive (goTree t) . goTree) mt)
+    goBranch acc (CondBranch _ t mt) = mergeInclusive acc (maybe (goTree t) (mergeExclusive (goTree t) . goTree) mt)
\ No newline at end of file
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 037e40f1f15..96d8d26feca 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -50,13 +50,13 @@ import Distribution.Package
 import Distribution.Types.SourceRepo (RepoType)
 import Distribution.Types.CondTree (CondTree (..), CondBranch (..), condIfThen, condIfThenElse, mapTreeConds)
 import Distribution.PackageDescription
-         ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment (..) )
+         ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment)
 import Distribution.PackageDescription.Configuration (simplifyWithSysParams)
 import Distribution.Simple.Compiler
          ( OptimisationLevel(..), DebugInfoLevel(..), CompilerInfo(..) )
 import Distribution.Simple.InstallDirs ( CopyDest (NoCopyDest) )
 import Distribution.Simple.Setup
-         ( Flag(Flag), toFlag, fromFlagOrDefault
+         ( Flag(..), toFlag, fromFlagOrDefault
          , ConfigFlags(..), configureOptions
          , HaddockFlags(..), haddockOptions, defaultHaddockFlags
          , TestFlags(..), testOptions', defaultTestFlags
@@ -86,12 +86,14 @@ import Distribution.Deprecated.ReadP
 import qualified Text.PrettyPrint as Disp
 import Text.PrettyPrint
          ( Doc, ($+$) )
+import qualified Text.Parsec.Error as P
+import qualified Text.Parsec.Pos as P
 import qualified Distribution.Deprecated.ParseUtils as ParseUtils
 import Distribution.Deprecated.ParseUtils
          ( ParseResult(..), PError(..), syntaxError, PWarning(..)
          , commaNewLineListFieldParsec, newLineListField, parseTokenQ
          , parseHaskellString, showToken
-         , simpleFieldParsec
+         , simpleFieldParsec, parseFail
          )
 import Distribution.Client.ParseUtils
 import Distribution.Simple.Command
@@ -99,18 +101,19 @@ import Distribution.Simple.Command
          , OptionField, option, reqArg' )
 import Distribution.Types.PackageVersionConstraint
          ( PackageVersionConstraint )
-import Distribution.Parsec (ParsecParser, zeroPos)
-import Distribution.System (Platform (..), OS, Arch)
+import Distribution.Parsec (ParsecParser)
+import Distribution.System (OS, Arch)
 
 import qualified Data.Map as Map
 import qualified Data.Set as Set
 import qualified Data.ByteString.Char8 as BS
 
-import Network.URI (URI (..))
+import Network.URI (URI (..), parseURI)
 
 import Distribution.Fields.ConfVar (parseConditionConfVarFromClause)
-import qualified Distribution.Fields.ParseResult as FPR
-import Distribution.Fields.Field (SectionArg (..))
+
+import Distribution.Client.HttpUtils
+import System.FilePath ((</>))
 
 
 
@@ -125,18 +128,11 @@ type ProjectConfigSkeleton = CondTree ConfVar [ProjectConfigImport] ProjectConfi
 type ProjectConfigImport = String
 
 
-instance Semigroup (CondTree ConfVar [ProjectConfigImport] ProjectConfig) where
-  (CondNode a c bs) <> (CondNode a' c' bs') = CondNode (a <> a') (c <> c') (bs <> bs')
-
-instance Monoid (CondTree ConfVar [ProjectConfigImport] ProjectConfig) where
-   mappend = (<>)
-   mempty = CondNode mempty mempty mempty
-
 singletonProjectConfigSkeleton :: ProjectConfig -> ProjectConfigSkeleton
 singletonProjectConfigSkeleton x = CondNode x mempty mempty
 
 instantiateProjectConfigSkeleton :: OS -> Arch -> CompilerInfo -> FlagAssignment -> ProjectConfigSkeleton -> ProjectConfig
-instantiateProjectConfigSkeleton os arch impl flags skel = go $ mapTreeConds (fst . simplifyWithSysParams os arch impl) skel -- TODO bail on flags
+instantiateProjectConfigSkeleton os arch impl _flags skel = go $ mapTreeConds (fst . simplifyWithSysParams os arch impl) skel
     where
         go :: CondTree
                FlagName
@@ -149,24 +145,21 @@ instantiateProjectConfigSkeleton os arch impl flags skel = go $ mapTreeConds (fs
         processBranch (CondBranch cnd t mf) = case cnd of
            (Lit True) ->  [go t]
            (Lit False) -> maybe ([]) ((:[]) . go) mf
-           _ -> []
-
-
--- TODO ensure parse doesn't have flags setting compiler inside conditionals
+           _ -> error $ "unable to process condition: " ++ show cnd -- TODO it would be nice if there were a pretty printer
 
 -- NOTE a nice refactor would be to use readFields directly to get a tree structure.
-parseProjectSkeleton :: FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
-parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
+parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
+parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWalkPCS False) . runInnerParsers <$> linesToNode (BS.lines bs)
  where
-  linesToNode :: [BS.ByteString] -> IO (CondTree ConfVar [ProjectConfigImport] [BS.ByteString])
+  linesToNode :: [BS.ByteString] -> IO (CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString])
   linesToNode ls = packResult . mconcat <$> go ls
 
-  packResult :: ([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree ConfVar [ProjectConfigImport] [BS.ByteString]
+  packResult :: ([CondBranch BS.ByteString [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString]
   packResult (branches, imps, ls) = CondNode ls imps branches
 
-  go :: [BS.ByteString] -> IO [([CondBranch ConfVar [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
+  go :: [BS.ByteString] -> IO [([CondBranch BS.ByteString [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
   go (l:ls)
-       | Just condition <- parseCond l =
+       | Just condition <- Var <$> detectCond l =
             let (clause, rest) = splitTillIndented ls
             in case rest of
                 (r:rs) | (BS.pack "else") `BS.isPrefixOf` r -> -- TODO handle elif
@@ -185,29 +178,59 @@ parseProjectSkeleton source bs = runInnerParsers <$> linesToNode (BS.lines bs)
 
   splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
 
-  parseCond :: BS.ByteString -> Maybe (Condition ConfVar)
-  parseCond l | (BS.pack "if(") `BS.isPrefixOf` l = case parseConditionConfVarFromClause l of
-                                                      Left err -> error (show err) -- TODO improve error reporting here
-                                                      Right x -> Just x
+  detectCond :: BS.ByteString -> Maybe BS.ByteString
+  detectCond l | (BS.pack "if(") `BS.isPrefixOf` l = Just l
 
               | otherwise = Nothing
   parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
                 | otherwise = Nothing
-  runInnerParsers :: CondTree ConfVar [ProjectConfigImport] [BS.ByteString] -> ParseResult ProjectConfigSkeleton
-  runInnerParsers = traverse (fmap (addProvenance . convertLegacyProjectConfig) . parseLegacyProjectConfig source . BS.unlines)
+  runInnerParsers :: CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString] -> ParseResult ProjectConfigSkeleton
+  runInnerParsers = (runConditionParsers =<<) . traverse (fmap (addProvenance . convertLegacyProjectConfig) . parseLegacyProjectConfig source . BS.unlines)
+
+  runConditionParsers :: (CondTree BS.ByteString [ProjectConfigImport] ProjectConfig) -> ParseResult ProjectConfigSkeleton
+  runConditionParsers (CondNode d c x) = CondNode d c <$> mapM runBranchConditionParser x
+
+  runBranchConditionParser :: CondBranch BS.ByteString [ProjectConfigImport] ProjectConfig -> ParseResult (CondBranch ConfVar [ProjectConfigImport] ProjectConfig)
+  runBranchConditionParser (CondBranch (Var b) t f) = do
+      c <- adaptParseError $ parseConditionConfVarFromClause b -- nb this loses the source line location, can't win 'em all, sigh. A full refactor of parsers is the "right" way to fix this.
+      CondBranch c <$> runConditionParsers t <*> traverse runConditionParsers f
+  runBranchConditionParser (CondBranch x _ _) = error $ "internal cabal invariant error in parsing branch conditions: " ++ show x
+
+  adaptParseError :: Either P.ParseError a -> ParseResult a
+  adaptParseError (Right x) = pure x
+  adaptParseError (Left e) = parseFail $ ParseUtils.NoParse (show e) (P.sourceLine $ P.errorPos e)
 
   addProvenance x = x {projectConfigProvenance = Set.singleton (Explicit source)}
 
+  modifiesCompiler :: ProjectConfig -> Bool
+  modifiesCompiler pc = isSet projectConfigHcFlavor || isSet projectConfigHcPath || isSet projectConfigHcPkg
+     where
+       isSet f = f (projectConfigShared pc) == NoFlag
+
+  sanityWalkPCS :: Bool -> ProjectConfigSkeleton -> ParseResult ProjectConfigSkeleton
+  sanityWalkPCS underConditional t@(CondNode d _c comps)
+           | underConditional && modifiesCompiler d = parseFail $ ParseUtils.NoParse "Cannot set compiler in a conditional clause of a cabal project file" 0
+           | otherwise = mapM_ sanityWalkBranch comps >> pure t
+
+  sanityWalkBranch:: CondBranch ConfVar [ProjectConfigImport] ProjectConfig -> ParseResult ()
+  sanityWalkBranch (CondBranch _c t f) = traverse (sanityWalkPCS True) f >> sanityWalkPCS True t >> pure ()
+
   fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
-  fetchImportConfig = BS.readFile -- todo, handle http
+  fetchImportConfig pci = case parseURI pci of
+    Just uri -> do
+       let fp = cacheDir </> show uri
+       _ <- downloadURI httpTransport verbosity uri fp
+       BS.readFile fp
+    Nothing -> BS.readFile pci
+
 
 {-
--- todo handlehttp
 -- todo add extra files to file change monitor
-
 -- TODO handle importing legacy freeze as well
 -- TODO handle merge semantics for constraints specially
 
+-- TODO somehow handle .local specially to avoid reconfig issues.
+
 -}
 
 ------------------------------------------------------------------

From 912205c9d743ccf2a557d5f521315dc49046ef21 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 3 Jan 2022 16:51:52 -0500
Subject: [PATCH 06/22] thread through http transport

---
 .../src/Distribution/Client/ProjectConfig.hs     | 16 +++++++++-------
 .../Distribution/Client/ProjectOrchestration.hs  | 11 +++++++++--
 .../src/Distribution/Client/ProjectPlanning.hs   |  5 ++++-
 cabal-install/tests/IntegrationTests2.hs         |  4 ++++
 4 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index c72f79bd9dd..5571cc02886 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -502,12 +502,13 @@ withProjectOrGlobalConfig' verbosity globalConfigFlag with without = do
 -- file if any, plus other global config.
 --
 readProjectConfig :: Verbosity
+                  -> HttpTransport
                   -> Flag FilePath
                   -> DistDirLayout
                   -> Rebuild ProjectConfigSkeleton
-readProjectConfig verbosity configFileFlag distDirLayout = do
+readProjectConfig verbosity httpTransport configFileFlag distDirLayout = do
     global <- singletonProjectConfigSkeleton <$> readGlobalConfig                verbosity configFileFlag
-    local  <- readProjectLocalConfigOrDefault verbosity distDirLayout
+    local  <- readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout
     freeze <- singletonProjectConfigSkeleton <$> readProjectLocalFreezeConfig    verbosity distDirLayout
     extra  <- singletonProjectConfigSkeleton <$> readProjectLocalExtraConfig     verbosity distDirLayout
     return (global <> local <> freeze <> extra)
@@ -517,13 +518,14 @@ readProjectConfig verbosity configFileFlag distDirLayout = do
 -- or returns the default project config for an implicitly defined project.
 --
 readProjectLocalConfigOrDefault :: Verbosity
+                                -> HttpTransport
                                 -> DistDirLayout
                                 -> Rebuild ProjectConfigSkeleton
-readProjectLocalConfigOrDefault verbosity distDirLayout = do
+readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout = do
   usesExplicitProjectRoot <- liftIO $ doesFileExist projectFile
   if usesExplicitProjectRoot
     then do
-      readProjectFileSkeleton verbosity distDirLayout "" "project file"
+      readProjectFileSkeleton verbosity httpTransport distDirLayout "" "project file"
     else do
       monitorFiles [monitorNonExistentFile projectFile]
       return (singletonProjectConfigSkeleton defaultImplicitProjectConfig)
@@ -563,8 +565,8 @@ readProjectLocalFreezeConfig verbosity distDirLayout =
 
 -- | Reads a named extended (with imports and conditionals) config file in the given project root dir, or returns empty.
 --
-readProjectFileSkeleton :: Verbosity -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
-readProjectFileSkeleton verbosity DistDirLayout{distProjectFile}
+readProjectFileSkeleton :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeleton verbosity httpTransport DistDirLayout{distProjectFile, distDownloadSrcDirectory}
                          extensionName extensionDescription = do
     exists <- liftIO $ doesFileExist extensionFile
     if exists
@@ -577,7 +579,7 @@ readProjectFileSkeleton verbosity DistDirLayout{distProjectFile}
 
     readExtensionFile =
           reportParseResult verbosity extensionDescription extensionFile
-      =<< parseProjectSkeleton extensionFile
+      =<< parseProjectSkeleton distDownloadSrcDirectory httpTransport verbosity extensionFile
       =<< BS.readFile extensionFile
 
 -- | Reads a named config file in the given project root dir, or returns empty.
diff --git a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
index d4de014a7de..d7933b6c2a9 100644
--- a/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
+++ b/cabal-install/src/Distribution/Client/ProjectOrchestration.hs
@@ -139,6 +139,7 @@ import qualified Distribution.Client.BuildReports.Storage as BuildReports
          ( storeLocal )
 
 import           Distribution.Client.Config (getCabalDir)
+import           Distribution.Client.HttpUtils
 import           Distribution.Client.Setup hiding (packageName)
 import           Distribution.Compiler
                    ( CompilerFlavor(GHC) )
@@ -170,7 +171,8 @@ import           Distribution.Version
 import           Distribution.Simple.Compiler
                    ( compilerCompatVersion, showCompilerId, compilerId, compilerInfo
                    , OptimisationLevel(..))
-
+import           Distribution.Utils.NubList
+                   ( fromNubList )
 import           Distribution.System
                    ( Platform(Platform) )
 
@@ -210,7 +212,7 @@ establishProjectBaseContext verbosity cliConfig currentCommand = do
     establishProjectBaseContextWithRoot verbosity cliConfig projectRoot currentCommand
   where
     mprojectFile   = Setup.flagToMaybe projectConfigProjectFile
-    ProjectConfigShared { projectConfigProjectFile } = projectConfigShared cliConfig
+    ProjectConfigShared { projectConfigProjectFile} = projectConfigShared cliConfig
 
 -- | Like 'establishProjectBaseContext' but doesn't search for project root.
 establishProjectBaseContextWithRoot
@@ -224,8 +226,13 @@ establishProjectBaseContextWithRoot verbosity cliConfig projectRoot currentComma
 
     let distDirLayout  = defaultDistDirLayout projectRoot mdistDirectory
 
+    httpTransport <- configureTransport verbosity
+                     (fromNubList . projectConfigProgPathExtra $ projectConfigShared cliConfig)
+                     (flagToMaybe . projectConfigHttpTransport $ projectConfigBuildOnly cliConfig)
+
     (projectConfig, localPackages) <-
       rebuildProjectConfig verbosity
+                           httpTransport
                            distDirLayout
                            cliConfig
 
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 7b5e23434d6..628dc7e9f40 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -71,6 +71,7 @@ import Prelude ()
 import Distribution.Client.Compat.Prelude
 
 import           Distribution.Client.HashValue
+import           Distribution.Client.HttpUtils
 import           Distribution.Client.ProjectPlanning.Types as Ty
 import           Distribution.Client.PackageHash
 import           Distribution.Client.RebuildMonad
@@ -301,11 +302,13 @@ sanityCheckElaboratedPackage ElaboratedConfiguredPackage{..}
 -- packages within the project.
 --
 rebuildProjectConfig :: Verbosity
+                     -> HttpTransport
                      -> DistDirLayout
                      -> ProjectConfig
                      -> IO ( ProjectConfig
                            , [PackageSpecifier UnresolvedSourcePackage] )
 rebuildProjectConfig verbosity
+                     httpTransport
                      distDirLayout@DistDirLayout {
                        distProjectRootDirectory,
                        distDirectory,
@@ -360,7 +363,7 @@ rebuildProjectConfig verbosity
     --
     phaseReadProjectConfig :: Rebuild ProjectConfigSkeleton
     phaseReadProjectConfig = do
-      readProjectConfig verbosity projectConfigConfigFile distDirLayout
+      readProjectConfig verbosity httpTransport projectConfigConfigFile distDirLayout
 
     -- Look for all the cabal packages in the project
     -- some of which may be local src dirs, tarballs etc
diff --git a/cabal-install/tests/IntegrationTests2.hs b/cabal-install/tests/IntegrationTests2.hs
index 4ca346930ed..700c4342c22 100644
--- a/cabal-install/tests/IntegrationTests2.hs
+++ b/cabal-install/tests/IntegrationTests2.hs
@@ -16,6 +16,7 @@ import Prelude ()
 import Distribution.Client.DistDirLayout
 import Distribution.Client.ProjectConfig
 import Distribution.Client.Config (getCabalDir)
+import Distribution.Client.HttpUtils
 import Distribution.Client.TargetSelector hiding (DirActions(..))
 import qualified Distribution.Client.TargetSelector as TS (DirActions(..))
 import Distribution.Client.ProjectPlanning
@@ -1511,8 +1512,11 @@ configureProject testdir cliConfig = do
     -- ended in an exception (as we leave the files to help with debugging).
     cleanProject testdir
 
+    httpTransport <- configureTransport verbosity [] Nothing
+
     (projectConfig, localPackages) <-
       rebuildProjectConfig verbosity
+                           httpTransport
                            distDirLayout
                            cliConfig
 

From e0607be72b96e0216b4624d40333837ae62bc863 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 3 Jan 2022 17:27:46 -0500
Subject: [PATCH 07/22] fix merge

---
 .../src/Distribution/Deprecated/ParseUtils.hs          | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/cabal-install/src/Distribution/Deprecated/ParseUtils.hs b/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
index c1a0e4cd30c..6ac62a6e82d 100644
--- a/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
+++ b/cabal-install/src/Distribution/Deprecated/ParseUtils.hs
@@ -105,6 +105,11 @@ instance Monad ParseResult where
         ParseOk ws x >>= f = case f x of
                                ParseFailed err -> ParseFailed err
                                ParseOk ws' x' -> ParseOk (ws'++ws) x'
+#if !(MIN_VERSION_base(4,9,0))
+        fail = parseResultFail
+#elif !(MIN_VERSION_base(4,13,0))
+        fail = Fail.fail
+#endif
 
 instance Foldable ParseResult where
   foldMap _ (ParseFailed _ ) = mempty
@@ -114,11 +119,6 @@ instance Traversable ParseResult where
   traverse _ (ParseFailed err) = pure (ParseFailed err)
   traverse f (ParseOk ws x) = ParseOk ws <$> f x
 
-#if !(MIN_VERSION_base(4,9,0))
-        fail = parseResultFail
-#elif !(MIN_VERSION_base(4,13,0))
-        fail = Fail.fail
-#endif
 
 instance Fail.MonadFail ParseResult where
         fail = parseResultFail

From ec3763fc871e4bb16140cbc418ba72e637981813 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 5 Jan 2022 15:59:03 -0500
Subject: [PATCH 08/22] better errors and use extended project parsing
 uniformly

---
 Cabal/src/Distribution/Types/CondTree.hs      |  2 +-
 .../src/Distribution/Client/CmdConfigure.hs   | 17 +++--
 .../src/Distribution/Client/CmdOutdated.hs    | 38 +++++++----
 .../src/Distribution/Client/ProjectConfig.hs  | 64 ++++---------------
 .../Client/ProjectConfig/Legacy.hs            | 31 +++++----
 .../Distribution/Client/ProjectPlanning.hs    |  1 +
 6 files changed, 71 insertions(+), 82 deletions(-)

diff --git a/Cabal/src/Distribution/Types/CondTree.hs b/Cabal/src/Distribution/Types/CondTree.hs
index 442e4b48b8c..8f1d17a8163 100644
--- a/Cabal/src/Distribution/Types/CondTree.hs
+++ b/Cabal/src/Distribution/Types/CondTree.hs
@@ -71,7 +71,7 @@ instance (NFData v, NFData c, NFData a) => NFData (CondTree v c a) where rnf = g
 instance (Semigroup a, Semigroup c) => Semigroup (CondTree v c a) where
   (CondNode a c bs) <> (CondNode a' c' bs') = CondNode (a <> a') (c <> c') (bs <> bs')
 
-instance (Monoid a, Monoid c) => Monoid (CondTree v c a) where
+instance (Semigroup a, Semigroup c, Monoid a, Monoid c) => Monoid (CondTree v c a) where
    mappend = (<>)
    mempty = CondNode mempty mempty mempty
 
diff --git a/cabal-install/src/Distribution/Client/CmdConfigure.hs b/cabal-install/src/Distribution/Client/CmdConfigure.hs
index f734f15c668..cfe4741d0bd 100644
--- a/cabal-install/src/Distribution/Client/CmdConfigure.hs
+++ b/cabal-install/src/Distribution/Client/CmdConfigure.hs
@@ -30,12 +30,17 @@ import Distribution.Verbosity
 import Distribution.Simple.Command
          ( CommandUI(..), usageAlternatives )
 import Distribution.Simple.Utils
-         ( wrapText, notice )
+         ( wrapText, notice, die' )
 
 import Distribution.Client.DistDirLayout
          ( DistDirLayout(..) )
 import Distribution.Client.RebuildMonad (runRebuild)
 import Distribution.Client.ProjectConfig.Types
+import Distribution.Client.HttpUtils
+import Distribution.Utils.NubList
+         ( fromNubList )
+import Distribution.Types.CondTree
+         ( CondTree (..) )
 
 configureCommand :: CommandUI (NixStyleFlags ())
 configureCommand = CommandUI {
@@ -126,9 +131,13 @@ configureAction' flags@NixStyleFlags {..} _extraArgs globalFlags = do
          -- If the flag @configAppend@ is set to true, append and do not overwrite
         if exists && appends
           then do
-            conf <- runRebuild (distProjectRootDirectory . distDirLayout $ baseCtx) $
-              readProjectLocalExtraConfig v (distDirLayout baseCtx)
-            return (baseCtx, conf <> cliConfig) -- TODO ugh. maybe don't have extra configs have conditions, only main configs
+            httpTransport <- configureTransport v
+                     (fromNubList . projectConfigProgPathExtra $ projectConfigShared cliConfig)
+                     (flagToMaybe . projectConfigHttpTransport $ projectConfigBuildOnly cliConfig)
+            (CondNode conf imps bs)  <- runRebuild (distProjectRootDirectory . distDirLayout $ baseCtx) $
+              readProjectLocalExtraConfig v httpTransport (distDirLayout baseCtx)
+            when (not (null imps && null bs)) $ die' v "local project file has conditional and/or import logic, unable to perform and automatic in-place update"
+            return (baseCtx, conf <> cliConfig)
           else
             return (baseCtx, cliConfig)
   where
diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index b2b817a00ce..d09fdabe900 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -29,9 +29,10 @@ import Distribution.Client.DistDirLayout
     ( defaultDistDirLayout
     , DistDirLayout(distProjectRootDirectory, distProjectFile) )
 import Distribution.Client.ProjectConfig
-    ( ProjectConfig(projectConfigShared),
-      ProjectConfigShared(projectConfigConstraints), findProjectRoot,
-      readProjectLocalFreezeConfig )
+import Distribution.Client.ProjectConfig.Legacy
+    ( instantiateProjectConfigSkeleton )
+import Distribution.Client.ProjectPlanning
+    ( configureCompiler )
 import Distribution.Client.ProjectFlags
     ( projectFlagsOptions, ProjectFlags(..), defaultProjectFlags
     , removeIgnoreProjectOption )
@@ -40,8 +41,6 @@ import Distribution.Client.RebuildMonad
 import Distribution.Client.Sandbox
     ( loadConfigOrSandboxConfig )
 import Distribution.Client.Setup
-    ( withRepoContext, GlobalFlags, configCompilerAux'
-    , ConfigExFlags(configExConstraints) )
 import Distribution.Client.Targets
     ( userToPackageConstraint, UserConstraint )
 import Distribution.Client.Types.SourcePackageDb as SourcePackageDb
@@ -55,7 +54,7 @@ import Distribution.Utils.Generic
 import Distribution.Package
     ( PackageName, packageVersion )
 import Distribution.PackageDescription
-    ( allBuildDepends )
+    ( allBuildDepends, ignoreConditions )
 import Distribution.PackageDescription.Configuration
     ( finalizePD )
 import Distribution.Simple.Compiler
@@ -65,7 +64,7 @@ import Distribution.Simple.Setup
 import Distribution.Simple.Utils
     ( die', notice, debug, tryFindPackageDesc )
 import Distribution.System
-    ( Platform )
+    ( Platform (..) )
 import Distribution.Types.ComponentRequestedSpec
     ( ComponentRequestedSpec(..) )
 import Distribution.Types.Dependency
@@ -86,6 +85,10 @@ import Distribution.Simple.Command
 import qualified Distribution.Compat.CharParsing as P
 import Distribution.ReadE
     ( parsecToReadE )
+import Distribution.Client.HttpUtils
+import Distribution.Utils.NubList
+         ( fromNubList )
+
 
 import qualified Data.Set as S
 import System.Directory
@@ -220,7 +223,6 @@ outdatedAction (ProjectFlags{flagProjectFileName}, OutdatedFlags{..}) _targetStr
   config <- loadConfigOrSandboxConfig verbosity globalFlags
   let globalFlags' = savedGlobalFlags config `mappend` globalFlags
       configFlags  = savedConfigureFlags config
-  (comp, platform, _progdb) <- configCompilerAux' configFlags
   withRepoContext verbosity globalFlags' $ \repoContext -> do
     when (not newFreezeFile && isJust mprojectFile) $
       die' verbosity $
@@ -230,8 +232,14 @@ outdatedAction (ProjectFlags{flagProjectFileName}, OutdatedFlags{..}) _targetStr
     deps <- if freezeFile
             then depsFromFreezeFile verbosity
             else if newFreezeFile
-                then depsFromNewFreezeFile verbosity mprojectFile
-                else depsFromPkgDesc verbosity comp platform
+                then do
+                       httpTransport <- configureTransport verbosity
+                         (fromNubList . globalProgPathExtra $ globalFlags)
+                         (flagToMaybe . globalHttpTransport $ globalFlags)
+                       depsFromNewFreezeFile verbosity httpTransport mprojectFile
+                else do
+                  (comp, platform, _progdb) <- configCompilerAux' configFlags
+                  depsFromPkgDesc verbosity comp platform
     debug verbosity $ "Dependencies loaded: "
       ++ intercalate ", " (map prettyShow deps)
     let outdatedDeps = listOutdated deps sourcePkgDb
@@ -293,14 +301,16 @@ depsFromFreezeFile verbosity = do
   return deps
 
 -- | Read the list of dependencies from the new-style freeze file.
-depsFromNewFreezeFile :: Verbosity -> Maybe FilePath -> IO [PackageVersionConstraint]
-depsFromNewFreezeFile verbosity mprojectFile = do
+depsFromNewFreezeFile :: Verbosity -> HttpTransport -> Maybe FilePath -> IO [PackageVersionConstraint]
+depsFromNewFreezeFile verbosity httpTransport mprojectFile = do
   projectRoot <- either throwIO return =<<
                  findProjectRoot Nothing mprojectFile
   let distDirLayout = defaultDistDirLayout projectRoot
                       {- TODO: Support dist dir override -} Nothing
-  projectConfig  <- runRebuild (distProjectRootDirectory distDirLayout) $
-                    readProjectLocalFreezeConfig verbosity distDirLayout
+  projectConfig <- runRebuild (distProjectRootDirectory distDirLayout) $ do
+                      pcs <- readProjectLocalFreezeConfig verbosity httpTransport distDirLayout
+                      (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout (fst $ ignoreConditions pcs)
+                      pure $ instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty pcs
   let ucnstrs = map fst . projectConfigConstraints . projectConfigShared
                 $ projectConfig
       deps    = userConstraintsToDependencies ucnstrs
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index f879c61d5e8..c1811902c3d 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -507,10 +507,10 @@ readProjectConfig :: Verbosity
                   -> DistDirLayout
                   -> Rebuild ProjectConfigSkeleton
 readProjectConfig verbosity httpTransport configFileFlag distDirLayout = do
-    global <- singletonProjectConfigSkeleton <$> readGlobalConfig                verbosity configFileFlag
+    global <- singletonProjectConfigSkeleton <$> readGlobalConfig verbosity configFileFlag
     local  <- readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout
-    freeze <- singletonProjectConfigSkeleton <$> readProjectLocalFreezeConfig    verbosity distDirLayout
-    extra  <- singletonProjectConfigSkeleton <$> readProjectLocalExtraConfig     verbosity distDirLayout
+    freeze <- readProjectLocalFreezeConfig    verbosity httpTransport distDirLayout
+    extra  <- readProjectLocalExtraConfig     verbosity httpTransport distDirLayout
     return (global <> local <> freeze <> extra)
 
 
@@ -547,20 +547,20 @@ readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout = do
 -- or returns empty. This file gets written by @cabal configure@, or in
 -- principle can be edited manually or by other tools.
 --
-readProjectLocalExtraConfig :: Verbosity -> DistDirLayout
-                            -> Rebuild ProjectConfig
-readProjectLocalExtraConfig verbosity distDirLayout =
-    readProjectFile verbosity distDirLayout "local"
+readProjectLocalExtraConfig :: Verbosity -> HttpTransport -> DistDirLayout
+                            -> Rebuild ProjectConfigSkeleton
+readProjectLocalExtraConfig verbosity httpTransport distDirLayout =
+    readProjectFileSkeleton verbosity httpTransport distDirLayout "local"
                              "project local configuration file"
 
 -- | Reads a @cabal.project.freeze@ file in the given project root dir,
 -- or returns empty. This file gets written by @cabal freeze@, or in
 -- principle can be edited manually or by other tools.
 --
-readProjectLocalFreezeConfig :: Verbosity -> DistDirLayout
-                             -> Rebuild ProjectConfig
-readProjectLocalFreezeConfig verbosity distDirLayout =
-    readProjectFile verbosity distDirLayout "freeze"
+readProjectLocalFreezeConfig :: Verbosity -> HttpTransport ->DistDirLayout
+                             -> Rebuild ProjectConfigSkeleton
+readProjectLocalFreezeConfig verbosity httpTransport distDirLayout =
+    readProjectFileSkeleton verbosity httpTransport distDirLayout "freeze"
                              "project freeze file"
 
 -- | Reads a named extended (with imports and conditionals) config file in the given project root dir, or returns empty.
@@ -571,7 +571,9 @@ readProjectFileSkeleton verbosity httpTransport DistDirLayout{distProjectFile, d
     exists <- liftIO $ doesFileExist extensionFile
     if exists
       then do monitorFiles [monitorFileHashed extensionFile]
-              liftIO readExtensionFile
+              pcs <- liftIO readExtensionFile
+              monitorFiles $ map monitorFileHashed (projectSkeletonImports pcs)
+              pure pcs
       else do monitorFiles [monitorNonExistentFile extensionFile]
               return mempty
   where
@@ -582,44 +584,6 @@ readProjectFileSkeleton verbosity httpTransport DistDirLayout{distProjectFile, d
       =<< parseProjectSkeleton distDownloadSrcDirectory httpTransport verbosity extensionFile
       =<< BS.readFile extensionFile
 
--- | Reads a named config file in the given project root dir, or returns empty.
---
-readProjectFile :: Verbosity -> DistDirLayout -> String -> String -> Rebuild ProjectConfig
-readProjectFile verbosity DistDirLayout{distProjectFile}
-                         extensionName extensionDescription = do
-    exists <- liftIO $ doesFileExist extensionFile
-    if exists
-      then do monitorFiles [monitorFileHashed extensionFile]
-              addProjectFileProvenance <$> liftIO readExtensionFile
-      else do monitorFiles [monitorNonExistentFile extensionFile]
-              return mempty
-  where
-    extensionFile :: FilePath
-    extensionFile = distProjectFile extensionName
-
-    readExtensionFile :: IO ProjectConfig
-    readExtensionFile =
-          reportParseResult verbosity extensionDescription extensionFile
-        . (parseProjectConfig extensionFile)
-      =<< BS.readFile extensionFile
-
-    addProjectFileProvenance :: ProjectConfig -> ProjectConfig
-    addProjectFileProvenance config =
-      config {
-        projectConfigProvenance = Set.insert (Explicit extensionFile) (projectConfigProvenance config)
-      }
-
-
--- | Parse the 'ProjectConfig' format.
---
--- For the moment this is implemented in terms of parsers for legacy
--- configuration types, plus a conversion.
---
-parseProjectConfig :: FilePath -> BS.ByteString -> OldParser.ParseResult ProjectConfig
-parseProjectConfig source content =
-    convertLegacyProjectConfig <$>
-      (parseLegacyProjectConfig source content)
-
 -- | Render the 'ProjectConfig' format.
 --
 -- For the moment this is implemented in terms of a pretty printer for the
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 96d8d26feca..7d3d084beb5 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -9,6 +9,7 @@ module Distribution.Client.ProjectConfig.Legacy (
     parseProjectSkeleton,
     instantiateProjectConfigSkeleton,
     singletonProjectConfigSkeleton,
+    projectSkeletonImports,
 
     -- * Project config in terms of legacy types
     LegacyProjectConfig,
@@ -43,14 +44,17 @@ import Distribution.Client.CmdInstall.ClientInstallFlags
          ( ClientInstallFlags(..), defaultClientInstallFlags
          , clientInstallOptions )
 
+import Distribution.Compat.Lens (view)
+
 import Distribution.Solver.Types.ConstraintSource
 
 import Distribution.FieldGrammar
 import Distribution.Package
 import Distribution.Types.SourceRepo (RepoType)
-import Distribution.Types.CondTree (CondTree (..), CondBranch (..), condIfThen, condIfThenElse, mapTreeConds)
+import Distribution.Types.CondTree
+         ( CondTree (..), CondBranch (..), condIfThen, condIfThenElse, mapTreeConds, traverseCondTreeC )
 import Distribution.PackageDescription
-         ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment)
+         ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment )
 import Distribution.PackageDescription.Configuration (simplifyWithSysParams)
 import Distribution.Simple.Compiler
          ( OptimisationLevel(..), DebugInfoLevel(..), CompilerInfo(..) )
@@ -113,7 +117,8 @@ import Network.URI (URI (..), parseURI)
 import Distribution.Fields.ConfVar (parseConditionConfVarFromClause)
 
 import Distribution.Client.HttpUtils
-import System.FilePath ((</>))
+import System.FilePath ((</>), isPathSeparator)
+import System.Directory (createDirectoryIfMissing)
 
 
 
@@ -147,6 +152,9 @@ instantiateProjectConfigSkeleton os arch impl _flags skel = go $ mapTreeConds (f
            (Lit False) -> maybe ([]) ((:[]) . go) mf
            _ -> error $ "unable to process condition: " ++ show cnd -- TODO it would be nice if there were a pretty printer
 
+projectSkeletonImports :: ProjectConfigSkeleton -> [ProjectConfigImport]
+projectSkeletonImports = view traverseCondTreeC
+
 -- NOTE a nice refactor would be to use readFields directly to get a tree structure.
 parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
 parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWalkPCS False) . runInnerParsers <$> linesToNode (BS.lines bs)
@@ -192,24 +200,24 @@ parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWal
 
   runBranchConditionParser :: CondBranch BS.ByteString [ProjectConfigImport] ProjectConfig -> ParseResult (CondBranch ConfVar [ProjectConfigImport] ProjectConfig)
   runBranchConditionParser (CondBranch (Var b) t f) = do
-      c <- adaptParseError $ parseConditionConfVarFromClause b -- nb this loses the source line location, can't win 'em all, sigh. A full refactor of parsers is the "right" way to fix this.
+      c <- adaptParseError $ parseConditionConfVarFromClause b -- nb this loses the source line location, can't win 'em all, sigh. A full refactor of parsers is the "right" way to fix this. We could also pack bytestrings for conditionals with line locations
       CondBranch c <$> runConditionParsers t <*> traverse runConditionParsers f
   runBranchConditionParser (CondBranch x _ _) = error $ "internal cabal invariant error in parsing branch conditions: " ++ show x
 
   adaptParseError :: Either P.ParseError a -> ParseResult a
   adaptParseError (Right x) = pure x
-  adaptParseError (Left e) = parseFail $ ParseUtils.NoParse (show e) (P.sourceLine $ P.errorPos e)
+  adaptParseError (Left e) = parseFail $ ParseUtils.FromString (show e) (Just . P.sourceLine $ P.errorPos e)
 
   addProvenance x = x {projectConfigProvenance = Set.singleton (Explicit source)}
 
   modifiesCompiler :: ProjectConfig -> Bool
   modifiesCompiler pc = isSet projectConfigHcFlavor || isSet projectConfigHcPath || isSet projectConfigHcPkg
      where
-       isSet f = f (projectConfigShared pc) == NoFlag
+       isSet f = f (projectConfigShared pc) /= NoFlag
 
   sanityWalkPCS :: Bool -> ProjectConfigSkeleton -> ParseResult ProjectConfigSkeleton
   sanityWalkPCS underConditional t@(CondNode d _c comps)
-           | underConditional && modifiesCompiler d = parseFail $ ParseUtils.NoParse "Cannot set compiler in a conditional clause of a cabal project file" 0
+           | underConditional && modifiesCompiler d = parseFail $ ParseUtils.FromString "Cannot set compiler in a conditional clause of a cabal project file" Nothing
            | otherwise = mapM_ sanityWalkBranch comps >> pure t
 
   sanityWalkBranch:: CondBranch ConfVar [ProjectConfigImport] ProjectConfig -> ParseResult ()
@@ -218,19 +226,16 @@ parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWal
   fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
   fetchImportConfig pci = case parseURI pci of
     Just uri -> do
-       let fp = cacheDir </> show uri
+       let fp = cacheDir </> map (\x -> if isPathSeparator x then 'X' else x) (show uri) -- TODO can we do better?
+       createDirectoryIfMissing True cacheDir
        _ <- downloadURI httpTransport verbosity uri fp
        BS.readFile fp
     Nothing -> BS.readFile pci
 
 
 {-
--- todo add extra files to file change monitor
--- TODO handle importing legacy freeze as well
+-- TODO elif
 -- TODO handle merge semantics for constraints specially
-
--- TODO somehow handle .local specially to avoid reconfig issues.
-
 -}
 
 ------------------------------------------------------------------
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 628dc7e9f40..3f05be33487 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -40,6 +40,7 @@ module Distribution.Client.ProjectPlanning (
     -- * Utils required for building
     pkgHasEphemeralBuildTargets,
     elabBuildTargetWholeComponents,
+    configureCompiler,
 
     -- * Setup.hs CLI flags for building
     setupHsScriptOptions,

From 21ebfc1a9f64fe19064c0026bac0651f57ade23d Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 5 Jan 2022 18:11:51 -0500
Subject: [PATCH 09/22] elif support, maybe?

---
 .../Client/ProjectConfig/Legacy.hs            | 64 +++++++++++--------
 1 file changed, 37 insertions(+), 27 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 7d3d084beb5..4454a58615e 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -159,39 +159,55 @@ projectSkeletonImports = view traverseCondTreeC
 parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
 parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWalkPCS False) . runInnerParsers <$> linesToNode (BS.lines bs)
  where
+  -- converts lines to a full tree node, recursively looping "go" to pull out conditional and import structure, then packing the whole thing up
   linesToNode :: [BS.ByteString] -> IO (CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString])
-  linesToNode ls = packResult . mconcat <$> go ls
-
-  packResult :: ([CondBranch BS.ByteString [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString]) -> CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString]
-  packResult (branches, imps, ls) = CondNode ls imps branches
+  linesToNode xs = (\(branches, imps, ls) -> CondNode ls imps branches) . mconcat <$> go xs
 
+  -- given a list of lines, pulls out the conditional and import structure
   go :: [BS.ByteString] -> IO [([CondBranch BS.ByteString [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
   go (l:ls)
-       | Just condition <- Var <$> detectCond l =
-            let (clause, rest) = splitTillIndented ls
-            in case rest of
-                (r:rs) | (BS.pack "else") `BS.isPrefixOf` r -> -- TODO handle elif
-                     let (elseClause, lastRest) = splitTillIndented rs
-                     in do
-                        c1 <- linesToNode clause
-                        c2 <- linesToNode elseClause
-                        (([condIfThenElse condition c1 c2], [], []) :) <$> go lastRest
-                _ -> do
-                     c1 <- linesToNode clause
-                     (([condIfThen condition c1], [], []) :) <$>  go rest
+       | (BS.pack "if(") `BS.isPrefixOf` l =
+            let (clause, rest) = splitWhileIndented ls
+
+                -- unpacks the results of loop into nested if else clauses
+                constructNestedConds topCond topClause [] [] =
+                        do c1 <- linesToNode topClause
+                           pure $ condIfThen (Var topCond) c1
+                constructNestedConds topCond topClause ((elifCond, elifClause):elifs) elseClause =
+                        do c1 <- linesToNode topClause
+                           condIfThenElse (Var topCond) c1 . CondNode [] [] . (:[]) <$> constructNestedConds elifCond elifClause elifs elseClause
+                constructNestedConds topCond topClause [] elseClause =
+                        do c1 <- linesToNode topClause
+                           c2 <- linesToNode elseClause
+                           pure $ condIfThenElse (Var topCond) c1 c2
+
+                -- parse out the full list of if/else clauses
+                loop acc rss =
+                   case rss of
+                     (r:rs)
+                        | BS.pack "elif" `BS.isPrefixOf` r ->
+                            let (elseClause, lastRest) = splitWhileIndented rs
+                            in loop ((r, elseClause):acc) lastRest
+                        | BS.pack "else" `BS.isPrefixOf` r ->
+                            let (elseClause, lastRest) = splitWhileIndented rs
+                            in constructNestedConds l clause (reverse acc) elseClause
+                                  >>= (\c -> ((([c],[],[]) :) <$> go lastRest))
+                     _ -> constructNestedConds l clause (reverse acc) []
+                                  >>= (\c -> ((([c],[],[]) :) <$> go rss))
+            in loop [] rest
+
        | Just imp <- parseImport l = do x <- go . BS.lines =<< fetchImportConfig imp
                                         ((([], [imp], []) : x) ++) <$> go ls
+
        | otherwise = (([], [], [l]) :) <$> go ls
-  go [] = pure []
 
-  splitTillIndented = span ((BS.pack " ") `BS.isPrefixOf`)
+  go [] = pure []
 
-  detectCond :: BS.ByteString -> Maybe BS.ByteString
-  detectCond l | (BS.pack "if(") `BS.isPrefixOf` l = Just l
+  splitWhileIndented = span ((BS.pack " ") `BS.isPrefixOf`)
 
-              | otherwise = Nothing
   parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
                 | otherwise = Nothing
+
   runInnerParsers :: CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString] -> ParseResult ProjectConfigSkeleton
   runInnerParsers = (runConditionParsers =<<) . traverse (fmap (addProvenance . convertLegacyProjectConfig) . parseLegacyProjectConfig source . BS.unlines)
 
@@ -232,12 +248,6 @@ parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWal
        BS.readFile fp
     Nothing -> BS.readFile pci
 
-
-{-
--- TODO elif
--- TODO handle merge semantics for constraints specially
--}
-
 ------------------------------------------------------------------
 -- Representing the project config file in terms of legacy types
 --

From bd0031eac9762a67dbbd1bc6205f3507a4c9a631 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Thu, 6 Jan 2022 17:07:37 -0500
Subject: [PATCH 10/22] fix outdated cmd, add tests, docs

---
 .../src/Distribution/Client/CmdOutdated.hs    | 14 +++---
 .../Distribution/Client/ProjectPlanning.hs    | 48 -------------------
 .../PackageTests/ConditionalAndImport/Foo.hs  |  1 +
 .../ConditionalAndImport/cabal.out            | 12 +++++
 .../ConditionalAndImport/cabal.project        |  3 ++
 .../ConditionalAndImport/cabal.test.hs        |  4 ++
 .../ConditionalAndImport/extra.project        |  8 ++++
 .../ConditionalAndImport/my.cabal             |  9 ++++
 .../repo/some-exe-0.0.1.0/Main.hs             |  4 ++
 .../repo/some-exe-0.0.1.0/some-exe.cabal      |  9 ++++
 doc/cabal-project.rst                         | 25 ++++++++++
 11 files changed, 81 insertions(+), 56 deletions(-)
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/Foo.hs
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/my.cabal
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/Main.hs
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/some-exe.cabal

diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index d09fdabe900..7b9eb4a1c0a 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -31,8 +31,6 @@ import Distribution.Client.DistDirLayout
 import Distribution.Client.ProjectConfig
 import Distribution.Client.ProjectConfig.Legacy
     ( instantiateProjectConfigSkeleton )
-import Distribution.Client.ProjectPlanning
-    ( configureCompiler )
 import Distribution.Client.ProjectFlags
     ( projectFlagsOptions, ProjectFlags(..), defaultProjectFlags
     , removeIgnoreProjectOption )
@@ -54,7 +52,7 @@ import Distribution.Utils.Generic
 import Distribution.Package
     ( PackageName, packageVersion )
 import Distribution.PackageDescription
-    ( allBuildDepends, ignoreConditions )
+    ( allBuildDepends )
 import Distribution.PackageDescription.Configuration
     ( finalizePD )
 import Distribution.Simple.Compiler
@@ -94,6 +92,7 @@ import qualified Data.Set as S
 import System.Directory
     ( getCurrentDirectory, doesFileExist )
 
+
 -------------------------------------------------------------------------------
 -- Command
 -------------------------------------------------------------------------------
@@ -229,6 +228,7 @@ outdatedAction (ProjectFlags{flagProjectFileName}, OutdatedFlags{..}) _targetStr
         "--project-file must only be used with --v2-freeze-file."
 
     sourcePkgDb <- IndexUtils.getSourcePackages verbosity repoContext
+    (comp, platform, _progdb) <- configCompilerAux' configFlags
     deps <- if freezeFile
             then depsFromFreezeFile verbosity
             else if newFreezeFile
@@ -236,9 +236,8 @@ outdatedAction (ProjectFlags{flagProjectFileName}, OutdatedFlags{..}) _targetStr
                        httpTransport <- configureTransport verbosity
                          (fromNubList . globalProgPathExtra $ globalFlags)
                          (flagToMaybe . globalHttpTransport $ globalFlags)
-                       depsFromNewFreezeFile verbosity httpTransport mprojectFile
+                       depsFromNewFreezeFile verbosity httpTransport comp platform mprojectFile
                 else do
-                  (comp, platform, _progdb) <- configCompilerAux' configFlags
                   depsFromPkgDesc verbosity comp platform
     debug verbosity $ "Dependencies loaded: "
       ++ intercalate ", " (map prettyShow deps)
@@ -301,15 +300,14 @@ depsFromFreezeFile verbosity = do
   return deps
 
 -- | Read the list of dependencies from the new-style freeze file.
-depsFromNewFreezeFile :: Verbosity -> HttpTransport -> Maybe FilePath -> IO [PackageVersionConstraint]
-depsFromNewFreezeFile verbosity httpTransport mprojectFile = do
+depsFromNewFreezeFile :: Verbosity -> HttpTransport -> Compiler -> Platform -> Maybe FilePath -> IO [PackageVersionConstraint]
+depsFromNewFreezeFile verbosity httpTransport compiler (Platform arch os) mprojectFile = do
   projectRoot <- either throwIO return =<<
                  findProjectRoot Nothing mprojectFile
   let distDirLayout = defaultDistDirLayout projectRoot
                       {- TODO: Support dist dir override -} Nothing
   projectConfig <- runRebuild (distProjectRootDirectory distDirLayout) $ do
                       pcs <- readProjectLocalFreezeConfig verbosity httpTransport distDirLayout
-                      (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout (fst $ ignoreConditions pcs)
                       pure $ instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty pcs
   let ucnstrs = map fst . projectConfigConstraints . projectConfigShared
                 $ projectConfig
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 3f05be33487..304f0f0e6ea 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -40,7 +40,6 @@ module Distribution.Client.ProjectPlanning (
     -- * Utils required for building
     pkgHasEphemeralBuildTargets,
     elabBuildTargetWholeComponents,
-    configureCompiler,
 
     -- * Setup.hs CLI flags for building
     setupHsScriptOptions,
@@ -534,53 +533,6 @@ rebuildInstallPlan verbosity
     phaseConfigureCompiler :: ProjectConfig
                            -> Rebuild (Compiler, Platform, ProgramDb)
     phaseConfigureCompiler = configureCompiler verbosity distDirLayout
-{-
-    ProjectConfig {
-                             projectConfigShared = ProjectConfigShared {
-                               projectConfigHcFlavor,
-                               projectConfigHcPath,
-                               projectConfigHcPkg
-                             },
-                             projectConfigLocalPackages = PackageConfig {
-                               packageConfigProgramPaths,
-                               packageConfigProgramArgs,
-                               packageConfigProgramPathExtra
-                             }
-                           } = do
-        progsearchpath <- liftIO $ getSystemSearchPath
-        rerunIfChanged verbosity fileMonitorCompiler
-                       (hcFlavor, hcPath, hcPkg, progsearchpath,
-                        packageConfigProgramPaths,
-                        packageConfigProgramArgs,
-                        packageConfigProgramPathExtra) $ do
-
-          liftIO $ info verbosity "Compiler settings changed, reconfiguring..."
-          result@(_, _, progdb') <- liftIO $
-            Cabal.configCompilerEx
-              hcFlavor hcPath hcPkg
-              progdb verbosity
-
-        -- Note that we added the user-supplied program locations and args
-        -- for /all/ programs, not just those for the compiler prog and
-        -- compiler-related utils. In principle we don't know which programs
-        -- the compiler will configure (and it does vary between compilers).
-        -- We do know however that the compiler will only configure the
-        -- programs it cares about, and those are the ones we monitor here.
-          monitorFiles (programsMonitorFiles progdb')
-
-          return result
-      where
-        hcFlavor = flagToMaybe projectConfigHcFlavor
-        hcPath   = flagToMaybe projectConfigHcPath
-        hcPkg    = flagToMaybe projectConfigHcPkg
-        progdb   =
-            userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths))
-          . userSpecifyArgss (Map.toList (getMapMappend packageConfigProgramArgs))
-          . modifyProgramSearchPath
-              (++ [ ProgramSearchPathDir dir
-                  | dir <- fromNubList packageConfigProgramPathExtra ])
-          $ defaultProgramDb
--}
 
     -- Configuring other programs.
     --
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/Foo.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/Foo.hs
new file mode 100644
index 00000000000..efbf93bbde8
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/Foo.hs
@@ -0,0 +1 @@
+module Foo where
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
new file mode 100644
index 00000000000..b6a1f792e51
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
@@ -0,0 +1,12 @@
+# cabal v2-update
+Downloading the latest package list from test-local-repo
+# cabal v2-run
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - some-exe-0.0.1.0 (exe:some-exe) (requires build)
+Configuring some-exe-0.0.1.0...
+Preprocessing executable 'some-exe' for some-exe-0.0.1.0..
+Building executable 'some-exe' for some-exe-0.0.1.0..
+Installing executable some-exe in <PATH>
+Warning: The directory <ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/incoming/new-<RAND><ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/<PACKAGE>-<HASH>/bin is not in the system search path.
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
new file mode 100644
index 00000000000..8518c69bed4
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
@@ -0,0 +1,3 @@
+packages: .
+
+import extra.project
\ No newline at end of file
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
new file mode 100644
index 00000000000..06ba0db652c
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+main = cabalTest $
+  withRepo "repo" $ do
+     cabal "v2-run" [ "some-exe" ]
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project b/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
new file mode 100644
index 00000000000..f83687d44f9
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
@@ -0,0 +1,8 @@
+if(os(NoSuchOs) || False)
+  extra-packages: no-such-package
+elif(os(Whoops))
+  extra-packages: no-can-do
+elif(True)
+  extra-packages: some-exe
+else
+  extra-packages: nope
\ No newline at end of file
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/my.cabal b/cabal-testsuite/PackageTests/ConditionalAndImport/my.cabal
new file mode 100644
index 00000000000..b1b36c1e620
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/my.cabal
@@ -0,0 +1,9 @@
+name:           my
+version:        0.1
+license:        BSD3
+cabal-version:  >= 1.2
+build-type:     Simple
+
+library
+    exposed-modules:    Foo
+    build-depends:      base
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/Main.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/Main.hs
new file mode 100644
index 00000000000..33581fa8421
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/Main.hs
@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = putStrLn "hello world"
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/some-exe.cabal b/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/some-exe.cabal
new file mode 100644
index 00000000000..3a2e620d96e
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/repo/some-exe-0.0.1.0/some-exe.cabal
@@ -0,0 +1,9 @@
+name:           some-exe
+version:        0.0.1.0
+license:        BSD3
+cabal-version:  >= 1.2
+build-type:     Simple
+
+Executable some-exe
+  main-is: Main.hs
+  build-depends: base
diff --git a/doc/cabal-project.rst b/doc/cabal-project.rst
index 23083f9d0a9..5c911ca2f90 100644
--- a/doc/cabal-project.rst
+++ b/doc/cabal-project.rst
@@ -33,6 +33,31 @@ options):
 4. ``cabal.project.local`` (the output of ``cabal v2-configure``)
 
 
+Conditionals and imports
+------------------------
+
+As of ``cabal-install`` version 3.8, cabal supports conditional logic
+and imports in ``cabal.project`` files. Cabal supports
+:ref:`conditions` that case on operating system, architecture, and
+compiler x(i.e. there is no support for a notion of custom flags in
+project files). Imports may specify local filepaths or remote urls,
+and may reference either cabal.project files or v1-style cabal.config
+freeze files. As a usage example:
+
+::
+    if(os(darwin))
+      optimization: False
+    elif(os(freebsd))
+      packages: freebsd/*.cabal
+    else
+      optimization: True
+
+    import https://some.remote.source/subdir/cabal.config
+
+    import relativepath/extra-project.project
+
+    import /absolutepath/some-project.project
+
 Specifying the local packages
 -----------------------------
 

From e8ae8e048b7c530128d78431b25a3e36a479ef16 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Fri, 7 Jan 2022 13:12:40 -0500
Subject: [PATCH 11/22] fix docs

---
 doc/cabal-package.rst | 2 ++
 doc/cabal-project.rst | 7 ++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/doc/cabal-package.rst b/doc/cabal-package.rst
index 935dd1c8377..30e6b629be4 100644
--- a/doc/cabal-package.rst
+++ b/doc/cabal-package.rst
@@ -2559,6 +2559,8 @@ Since Cabal 2.2 conditional blocks support ``elif`` construct.
       else
            property-descriptions-or-conditionals
 
+.. _conditions:
+
 Conditions
 """"""""""
 
diff --git a/doc/cabal-project.rst b/doc/cabal-project.rst
index 5c911ca2f90..36aeed6e4b9 100644
--- a/doc/cabal-project.rst
+++ b/doc/cabal-project.rst
@@ -37,14 +37,15 @@ Conditionals and imports
 ------------------------
 
 As of ``cabal-install`` version 3.8, cabal supports conditional logic
-and imports in ``cabal.project`` files. Cabal supports
-:ref:`conditions` that case on operating system, architecture, and
-compiler x(i.e. there is no support for a notion of custom flags in
+and imports in ``cabal.project`` files. :ref:`conditions` in cabal
+projects not be nested, and may case on operating system, architecture, and
+compiler (i.e. there is no support for a notion of custom flags in
 project files). Imports may specify local filepaths or remote urls,
 and may reference either cabal.project files or v1-style cabal.config
 freeze files. As a usage example:
 
 ::
+
     if(os(darwin))
       optimization: False
     elif(os(freebsd))

From 189262c58edc9cd6efeb5b905abf614486cc4f0e Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Tue, 11 Jan 2022 13:11:59 -0500
Subject: [PATCH 12/22] use legacyReadFields parser

---
 .../src/Distribution/Client/ParseUtils.hs     |   1 -
 .../Client/ProjectConfig/Legacy.hs            | 170 ++++++++----------
 .../ConditionalAndImport/cabal.project        |   2 +-
 .../ConditionalAndImport/extra.project        |   2 +-
 doc/cabal-project.rst                         |   8 +-
 5 files changed, 81 insertions(+), 102 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ParseUtils.hs b/cabal-install/src/Distribution/Client/ParseUtils.hs
index ef94a167712..5a3319f1e31 100644
--- a/cabal-install/src/Distribution/Client/ParseUtils.hs
+++ b/cabal-install/src/Distribution/Client/ParseUtils.hs
@@ -365,4 +365,3 @@ parseConfig fieldDescrs sectionDescrs fgSectionDescrs empty str =
 --
 showConfig :: [FieldDescr a] -> [SectionDescr a] -> [FGSectionDescr FG.PrettyFieldGrammar a] -> a -> Disp.Doc
 showConfig = ppFieldsAndSections
-
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 4454a58615e..69a6a9a2e7b 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -52,7 +52,7 @@ import Distribution.FieldGrammar
 import Distribution.Package
 import Distribution.Types.SourceRepo (RepoType)
 import Distribution.Types.CondTree
-         ( CondTree (..), CondBranch (..), condIfThen, condIfThenElse, mapTreeConds, traverseCondTreeC )
+         ( CondTree (..), CondBranch (..), mapTreeConds, traverseCondTreeC )
 import Distribution.PackageDescription
          ( dispFlagAssignment, Condition (..), ConfVar (..), FlagAssignment )
 import Distribution.PackageDescription.Configuration (simplifyWithSysParams)
@@ -90,8 +90,6 @@ import Distribution.Deprecated.ReadP
 import qualified Text.PrettyPrint as Disp
 import Text.PrettyPrint
          ( Doc, ($+$) )
-import qualified Text.Parsec.Error as P
-import qualified Text.Parsec.Pos as P
 import qualified Distribution.Deprecated.ParseUtils as ParseUtils
 import Distribution.Deprecated.ParseUtils
          ( ParseResult(..), PError(..), syntaxError, PWarning(..)
@@ -155,98 +153,78 @@ instantiateProjectConfigSkeleton os arch impl _flags skel = go $ mapTreeConds (f
 projectSkeletonImports :: ProjectConfigSkeleton -> [ProjectConfigImport]
 projectSkeletonImports = view traverseCondTreeC
 
--- NOTE a nice refactor would be to use readFields directly to get a tree structure.
 parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
-parseProjectSkeleton cacheDir httpTransport verbosity source bs = (>>= sanityWalkPCS False) . runInnerParsers <$> linesToNode (BS.lines bs)
- where
-  -- converts lines to a full tree node, recursively looping "go" to pull out conditional and import structure, then packing the whole thing up
-  linesToNode :: [BS.ByteString] -> IO (CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString])
-  linesToNode xs = (\(branches, imps, ls) -> CondNode ls imps branches) . mconcat <$> go xs
-
-  -- given a list of lines, pulls out the conditional and import structure
-  go :: [BS.ByteString] -> IO [([CondBranch BS.ByteString [ProjectConfigImport] [BS.ByteString]], [ProjectConfigImport], [BS.ByteString])]
-  go (l:ls)
-       | (BS.pack "if(") `BS.isPrefixOf` l =
-            let (clause, rest) = splitWhileIndented ls
-
-                -- unpacks the results of loop into nested if else clauses
-                constructNestedConds topCond topClause [] [] =
-                        do c1 <- linesToNode topClause
-                           pure $ condIfThen (Var topCond) c1
-                constructNestedConds topCond topClause ((elifCond, elifClause):elifs) elseClause =
-                        do c1 <- linesToNode topClause
-                           condIfThenElse (Var topCond) c1 . CondNode [] [] . (:[]) <$> constructNestedConds elifCond elifClause elifs elseClause
-                constructNestedConds topCond topClause [] elseClause =
-                        do c1 <- linesToNode topClause
-                           c2 <- linesToNode elseClause
-                           pure $ condIfThenElse (Var topCond) c1 c2
-
-                -- parse out the full list of if/else clauses
-                loop acc rss =
-                   case rss of
-                     (r:rs)
-                        | BS.pack "elif" `BS.isPrefixOf` r ->
-                            let (elseClause, lastRest) = splitWhileIndented rs
-                            in loop ((r, elseClause):acc) lastRest
-                        | BS.pack "else" `BS.isPrefixOf` r ->
-                            let (elseClause, lastRest) = splitWhileIndented rs
-                            in constructNestedConds l clause (reverse acc) elseClause
-                                  >>= (\c -> ((([c],[],[]) :) <$> go lastRest))
-                     _ -> constructNestedConds l clause (reverse acc) []
-                                  >>= (\c -> ((([c],[],[]) :) <$> go rss))
-            in loop [] rest
-
-       | Just imp <- parseImport l = do x <- go . BS.lines =<< fetchImportConfig imp
-                                        ((([], [imp], []) : x) ++) <$> go ls
-
-       | otherwise = (([], [], [l]) :) <$> go ls
-
-  go [] = pure []
-
-  splitWhileIndented = span ((BS.pack " ") `BS.isPrefixOf`)
-
-  parseImport l | (BS.pack "import ") `BS.isPrefixOf` l = Just . BS.unpack $ BS.drop (length "import ") l
-                | otherwise = Nothing
-
-  runInnerParsers :: CondTree BS.ByteString [ProjectConfigImport] [BS.ByteString] -> ParseResult ProjectConfigSkeleton
-  runInnerParsers = (runConditionParsers =<<) . traverse (fmap (addProvenance . convertLegacyProjectConfig) . parseLegacyProjectConfig source . BS.unlines)
-
-  runConditionParsers :: (CondTree BS.ByteString [ProjectConfigImport] ProjectConfig) -> ParseResult ProjectConfigSkeleton
-  runConditionParsers (CondNode d c x) = CondNode d c <$> mapM runBranchConditionParser x
-
-  runBranchConditionParser :: CondBranch BS.ByteString [ProjectConfigImport] ProjectConfig -> ParseResult (CondBranch ConfVar [ProjectConfigImport] ProjectConfig)
-  runBranchConditionParser (CondBranch (Var b) t f) = do
-      c <- adaptParseError $ parseConditionConfVarFromClause b -- nb this loses the source line location, can't win 'em all, sigh. A full refactor of parsers is the "right" way to fix this. We could also pack bytestrings for conditionals with line locations
-      CondBranch c <$> runConditionParsers t <*> traverse runConditionParsers f
-  runBranchConditionParser (CondBranch x _ _) = error $ "internal cabal invariant error in parsing branch conditions: " ++ show x
-
-  adaptParseError :: Either P.ParseError a -> ParseResult a
-  adaptParseError (Right x) = pure x
-  adaptParseError (Left e) = parseFail $ ParseUtils.FromString (show e) (Just . P.sourceLine $ P.errorPos e)
-
-  addProvenance x = x {projectConfigProvenance = Set.singleton (Explicit source)}
-
-  modifiesCompiler :: ProjectConfig -> Bool
-  modifiesCompiler pc = isSet projectConfigHcFlavor || isSet projectConfigHcPath || isSet projectConfigHcPkg
-     where
-       isSet f = f (projectConfigShared pc) /= NoFlag
-
-  sanityWalkPCS :: Bool -> ProjectConfigSkeleton -> ParseResult ProjectConfigSkeleton
-  sanityWalkPCS underConditional t@(CondNode d _c comps)
+parseProjectSkeleton cacheDir httpTransport verbosity source bs = (sanityWalkPCS False =<<) <$> liftPR (go []) (ParseUtils.readFields bs)
+  where
+    go :: [ParseUtils.Field] -> [ParseUtils.Field] -> IO (ParseResult ProjectConfigSkeleton)
+    go acc (x:xs) = case x of
+         (ParseUtils.F _l "import" importLoc) -> do
+            let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
+            res <- parseProjectSkeleton cacheDir httpTransport verbosity importLoc =<< fetchImportConfig importLoc
+            rest <- go [] xs
+            pure . fmap mconcat . sequence $ [fs, res, rest]
+         (ParseUtils.Section l "if" p xs') -> do
+                           subpcs <- go [] xs'
+                           let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
+                           (elseClauses, rest) <- parseElseClauses xs
+                           let condNode =  (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e]) <$>
+                                  -- we rewrap as as a section so the readFields lexer of the conditional parser doesn't get confused
+                                  adaptParseError l (parseConditionConfVarFromClause . BS.pack $ "if(" <> p <> ")") <*>
+                                  subpcs <*>
+                                  elseClauses
+                           pure . fmap mconcat . sequence $ [fs, condNode, rest]
+         _ -> go (x:acc) xs
+    go acc [] = pure . fmap singletonProjectConfigSkeleton . fieldsToConfig $ reverse acc
+
+    parseElseClauses :: [ParseUtils.Field] -> IO (ParseResult (Maybe ProjectConfigSkeleton), ParseResult ProjectConfigSkeleton)
+    parseElseClauses x = case x of
+         (ParseUtils.Section _l "else" _p xs':xs) -> do
+               subpcs <- go [] xs'
+               rest <- go [] xs
+               pure (Just <$> subpcs, rest)
+         (ParseUtils.Section l "elif" p xs':xs) -> do
+               subpcs <- go [] xs'
+               (elseClauses, rest) <- parseElseClauses xs
+               let condNode = (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e]) <$>
+                                  adaptParseError l (parseConditionConfVarFromClause . BS.pack $ "else("<> p <> ")") <*>
+                                  subpcs <*>
+                                  elseClauses
+               pure (Just <$> condNode, rest)
+         _ -> (\r -> (pure Nothing,r)) <$> go [] x
+
+    fieldsToConfig xs = fmap (addProvenance . convertLegacyProjectConfig) $ parseLegacyProjectConfigFields source xs
+    addProvenance x = x {projectConfigProvenance = Set.singleton (Explicit source)}
+
+    adaptParseError _ (Right x) = pure x
+    adaptParseError l (Left e) = parseFail $ ParseUtils.FromString (show e) (Just l)
+
+    liftPR :: (a -> IO (ParseResult b)) -> ParseResult a -> IO (ParseResult b)
+    liftPR f (ParseOk ws x) = addWarnings <$> f x
+       where addWarnings (ParseOk ws' x') = ParseOk (ws' ++ ws) x'
+             addWarnings x' = x'
+    liftPR _ (ParseFailed e) = pure $ ParseFailed e
+
+    fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
+    fetchImportConfig pci = case parseURI pci of
+         Just uri -> do
+            let fp = cacheDir </> map (\x -> if isPathSeparator x then 'X' else x) (show uri) -- TODO can we do better?
+            createDirectoryIfMissing True cacheDir
+            _ <- downloadURI httpTransport verbosity uri fp
+            BS.readFile fp
+         Nothing -> BS.readFile pci
+
+    modifiesCompiler :: ProjectConfig -> Bool
+    modifiesCompiler pc = isSet projectConfigHcFlavor || isSet projectConfigHcPath || isSet projectConfigHcPkg
+      where
+         isSet f = f (projectConfigShared pc) /= NoFlag
+
+    sanityWalkPCS :: Bool -> ProjectConfigSkeleton -> ParseResult ProjectConfigSkeleton
+    sanityWalkPCS underConditional t@(CondNode d _c comps)
            | underConditional && modifiesCompiler d = parseFail $ ParseUtils.FromString "Cannot set compiler in a conditional clause of a cabal project file" Nothing
            | otherwise = mapM_ sanityWalkBranch comps >> pure t
 
-  sanityWalkBranch:: CondBranch ConfVar [ProjectConfigImport] ProjectConfig -> ParseResult ()
-  sanityWalkBranch (CondBranch _c t f) = traverse (sanityWalkPCS True) f >> sanityWalkPCS True t >> pure ()
-
-  fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
-  fetchImportConfig pci = case parseURI pci of
-    Just uri -> do
-       let fp = cacheDir </> map (\x -> if isPathSeparator x then 'X' else x) (show uri) -- TODO can we do better?
-       createDirectoryIfMissing True cacheDir
-       _ <- downloadURI httpTransport verbosity uri fp
-       BS.readFile fp
-    Nothing -> BS.readFile pci
+    sanityWalkBranch:: CondBranch ConfVar [ProjectConfigImport] ProjectConfig -> ParseResult ()
+    sanityWalkBranch (CondBranch _c t f) = traverse (sanityWalkPCS True) f >> sanityWalkPCS True t >> pure ()
 
 ------------------------------------------------------------------
 -- Representing the project config file in terms of legacy types
@@ -999,16 +977,18 @@ convertToLegacyPerPackageConfig PackageConfig {..} =
 -- Parsing and showing the project config file
 --
 
-
-parseLegacyProjectConfig :: FilePath -> BS.ByteString -> ParseResult LegacyProjectConfig
-parseLegacyProjectConfig source =
-    parseConfig (legacyProjectConfigFieldDescrs constraintSrc)
+parseLegacyProjectConfigFields :: FilePath -> [ParseUtils.Field] -> ParseResult LegacyProjectConfig
+parseLegacyProjectConfigFields source =
+    parseFieldsAndSections (legacyProjectConfigFieldDescrs constraintSrc)
                 legacyPackageConfigSectionDescrs
                 legacyPackageConfigFGSectionDescrs
                 mempty
   where
     constraintSrc = ConstraintSourceProjectConfig source
 
+parseLegacyProjectConfig :: FilePath -> BS.ByteString -> ParseResult LegacyProjectConfig
+parseLegacyProjectConfig source bs = parseLegacyProjectConfigFields source =<< ParseUtils.readFields bs
+
 showLegacyProjectConfig :: LegacyProjectConfig -> String
 showLegacyProjectConfig config =
     Disp.render $
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
index 8518c69bed4..0aeed82370c 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.project
@@ -1,3 +1,3 @@
 packages: .
 
-import extra.project
\ No newline at end of file
+import: extra.project
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project b/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
index f83687d44f9..52a1f847fbb 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/extra.project
@@ -5,4 +5,4 @@ elif(os(Whoops))
 elif(True)
   extra-packages: some-exe
 else
-  extra-packages: nope
\ No newline at end of file
+  extra-packages: nope
diff --git a/doc/cabal-project.rst b/doc/cabal-project.rst
index 36aeed6e4b9..3049f20fed5 100644
--- a/doc/cabal-project.rst
+++ b/doc/cabal-project.rst
@@ -38,7 +38,7 @@ Conditionals and imports
 
 As of ``cabal-install`` version 3.8, cabal supports conditional logic
 and imports in ``cabal.project`` files. :ref:`conditions` in cabal
-projects not be nested, and may case on operating system, architecture, and
+may case on operating system, architecture, and
 compiler (i.e. there is no support for a notion of custom flags in
 project files). Imports may specify local filepaths or remote urls,
 and may reference either cabal.project files or v1-style cabal.config
@@ -53,11 +53,11 @@ freeze files. As a usage example:
     else
       optimization: True
 
-    import https://some.remote.source/subdir/cabal.config
+    import: https://some.remote.source/subdir/cabal.config
 
-    import relativepath/extra-project.project
+    import: relativepath/extra-project.project
 
-    import /absolutepath/some-project.project
+    import: /absolutepath/some-project.project
 
 Specifying the local packages
 -----------------------------

From 1233acf8e4ab2ead76c5796de5f11fa0a5f9bde8 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Tue, 1 Feb 2022 17:01:17 -0500
Subject: [PATCH 13/22] changelog

---
 changelog.d/pr-7783 | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 changelog.d/pr-7783

diff --git a/changelog.d/pr-7783 b/changelog.d/pr-7783
new file mode 100644
index 00000000000..f15e61fdef2
--- /dev/null
+++ b/changelog.d/pr-7783
@@ -0,0 +1,10 @@
+synopsis: Conditionals and imports in cabal.project files
+packages: cabal-install
+prs: #7783
+issues: #7556
+
+description: {
+
+Cabal.project files now allow conditional logic on compiler version, arch, etc. as well as imports of other local or remote project of freeze files (both old and new style).
+
+}

From 782892f4986f530fbe7deb447290ed1a5017468a Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 2 Feb 2022 11:30:34 -0500
Subject: [PATCH 14/22] cyclical import detection

---
 .../src/Distribution/Client/CmdOutdated.hs      |  2 --
 .../src/Distribution/Client/ProjectConfig.hs    |  2 +-
 .../Distribution/Client/ProjectConfig/Legacy.hs | 17 ++++++++++-------
 .../PackageTests/ConditionalAndImport/cabal.out |  3 +++
 .../ConditionalAndImport/cabal.test.hs          |  1 +
 5 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/CmdOutdated.hs b/cabal-install/src/Distribution/Client/CmdOutdated.hs
index 7753078c6d2..b38cfc02f8b 100644
--- a/cabal-install/src/Distribution/Client/CmdOutdated.hs
+++ b/cabal-install/src/Distribution/Client/CmdOutdated.hs
@@ -87,12 +87,10 @@ import Distribution.Client.HttpUtils
 import Distribution.Utils.NubList
          ( fromNubList )
 
-
 import qualified Data.Set as S
 import System.Directory
     ( getCurrentDirectory, doesFileExist )
 
-
 -------------------------------------------------------------------------------
 -- Command
 -------------------------------------------------------------------------------
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index c1811902c3d..223a3160146 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -581,7 +581,7 @@ readProjectFileSkeleton verbosity httpTransport DistDirLayout{distProjectFile, d
 
     readExtensionFile =
           reportParseResult verbosity extensionDescription extensionFile
-      =<< parseProjectSkeleton distDownloadSrcDirectory httpTransport verbosity extensionFile
+      =<< parseProjectSkeleton distDownloadSrcDirectory httpTransport verbosity [] extensionFile
       =<< BS.readFile extensionFile
 
 -- | Render the 'ProjectConfig' format.
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index c5b618193a6..bde47a19532 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -154,16 +154,19 @@ instantiateProjectConfigSkeleton os arch impl _flags skel = go $ mapTreeConds (f
 projectSkeletonImports :: ProjectConfigSkeleton -> [ProjectConfigImport]
 projectSkeletonImports = view traverseCondTreeC
 
-parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
-parseProjectSkeleton cacheDir httpTransport verbosity source bs = (sanityWalkPCS False =<<) <$> liftPR (go []) (ParseUtils.readFields bs)
+parseProjectSkeleton :: FilePath -> HttpTransport -> Verbosity -> [ProjectConfigImport] -> FilePath -> BS.ByteString -> IO (ParseResult ProjectConfigSkeleton)
+parseProjectSkeleton cacheDir httpTransport verbosity seenImports source bs = (sanityWalkPCS False =<<) <$> liftPR (go []) (ParseUtils.readFields bs)
   where
     go :: [ParseUtils.Field] -> [ParseUtils.Field] -> IO (ParseResult ProjectConfigSkeleton)
     go acc (x:xs) = case x of
-         (ParseUtils.F _l "import" importLoc) -> do
-            let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
-            res <- parseProjectSkeleton cacheDir httpTransport verbosity importLoc =<< fetchImportConfig importLoc
-            rest <- go [] xs
-            pure . fmap mconcat . sequence $ [fs, res, rest]
+         (ParseUtils.F l "import" importLoc) ->
+            if importLoc `elem` seenImports
+              then pure . parseFail $ ParseUtils.FromString ("cyclical import of " ++ importLoc) (Just l)
+              else do
+                let fs = fmap (\x -> CondNode x [importLoc] mempty) $ fieldsToConfig (reverse acc)
+                res <- parseProjectSkeleton cacheDir httpTransport verbosity (importLoc : seenImports) importLoc =<< fetchImportConfig importLoc
+                rest <- go [] xs
+                pure . fmap mconcat . sequence $ [fs, res, rest]
          (ParseUtils.Section l "if" p xs') -> do
                            subpcs <- go [] xs'
                            let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
index b6a1f792e51..acd94e8947b 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
@@ -10,3 +10,6 @@ Preprocessing executable 'some-exe' for some-exe-0.0.1.0..
 Building executable 'some-exe' for some-exe-0.0.1.0..
 Installing executable some-exe in <PATH>
 Warning: The directory <ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/incoming/new-<RAND><ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/<PACKAGE>-<HASH>/bin is not in the system search path.
+# cabal v2-build
+Error: cabal: Error parsing project file <ROOT>/cabal-cyclical.project:3:
+cyclical import of cabal-cyclical.project
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
index 06ba0db652c..f1f125207e2 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
@@ -2,3 +2,4 @@ import Test.Cabal.Prelude
 main = cabalTest $
   withRepo "repo" $ do
      cabal "v2-run" [ "some-exe" ]
+     fails $ cabal "v2-build" [ "--project=cabal-cyclical.project" ]

From 0fcc0b58dd959f51c9b705bc3bb89825c2e007b4 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 2 Feb 2022 12:18:18 -0500
Subject: [PATCH 15/22] fix shadowing

---
 cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index bde47a19532..fc31eb14151 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -163,7 +163,7 @@ parseProjectSkeleton cacheDir httpTransport verbosity seenImports source bs = (s
             if importLoc `elem` seenImports
               then pure . parseFail $ ParseUtils.FromString ("cyclical import of " ++ importLoc) (Just l)
               else do
-                let fs = fmap (\x -> CondNode x [importLoc] mempty) $ fieldsToConfig (reverse acc)
+                let fs = fmap (\z -> CondNode z [importLoc] mempty) $ fieldsToConfig (reverse acc)
                 res <- parseProjectSkeleton cacheDir httpTransport verbosity (importLoc : seenImports) importLoc =<< fetchImportConfig importLoc
                 rest <- go [] xs
                 pure . fmap mconcat . sequence $ [fs, res, rest]

From 9867fbcee3b638124edf412dc3743924b8666857 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 2 Feb 2022 15:27:10 -0500
Subject: [PATCH 16/22] add missing file

---
 .../PackageTests/ConditionalAndImport/cabal-cyclical.project   | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/cabal-cyclical.project

diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-cyclical.project b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-cyclical.project
new file mode 100644
index 00000000000..db226311abc
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-cyclical.project
@@ -0,0 +1,3 @@
+packages: .
+
+import: cabal-cyclical.project

From 5d59b1814e2cdb3d140a3bb95fd4492c8d089fe2 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Fri, 25 Mar 2022 16:30:19 -0400
Subject: [PATCH 17/22] finish merge

---
 .../src/Distribution/Client/ProjectConfig.hs  |  1 -
 .../Distribution/Client/ProjectPlanning.hs    | 44 +------------------
 .../src/Distribution/Client/ScriptUtils.hs    | 42 +++++++++++++++---
 3 files changed, 37 insertions(+), 50 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index 4292e1608bd..bb6f07d3b9c 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -29,7 +29,6 @@ module Distribution.Client.ProjectConfig (
     readGlobalConfig,
     readProjectLocalExtraConfig,
     readProjectLocalFreezeConfig,
-    parseProjectConfig,
     reportParseResult,
     showProjectConfig,
     withProjectOrGlobalConfig,
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index e5589b7e3c0..9ca461b9e6f 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -40,6 +40,7 @@ module Distribution.Client.ProjectPlanning (
     -- * Utils required for building
     pkgHasEphemeralBuildTargets,
     elabBuildTargetWholeComponents,
+    configureCompiler,
 
     -- * Setup.hs CLI flags for building
     setupHsScriptOptions,
@@ -532,48 +533,7 @@ rebuildInstallPlan verbosity
     --
     phaseConfigureCompiler :: ProjectConfig
                            -> Rebuild (Compiler, Platform, ProgramDb)
-    phaseConfigureCompiler ProjectConfig {
-                             projectConfigShared = ProjectConfigShared {
-                               projectConfigHcFlavor,
-                               projectConfigHcPath,
-                               projectConfigHcPkg
-                             },
-                             projectConfigLocalPackages = PackageConfig {
-                               packageConfigProgramPaths,
-                               packageConfigProgramPathExtra
-                             }
-                           } = do
-        progsearchpath <- liftIO $ getSystemSearchPath
-        rerunIfChanged verbosity fileMonitorCompiler
-                       (hcFlavor, hcPath, hcPkg, progsearchpath,
-                        packageConfigProgramPaths,
-                        packageConfigProgramPathExtra) $ do
-
-          liftIO $ info verbosity "Compiler settings changed, reconfiguring..."
-          result@(_, _, progdb') <- liftIO $
-            Cabal.configCompilerEx
-              hcFlavor hcPath hcPkg
-              progdb verbosity
-
-        -- Note that we added the user-supplied program locations and args
-        -- for /all/ programs, not just those for the compiler prog and
-        -- compiler-related utils. In principle we don't know which programs
-        -- the compiler will configure (and it does vary between compilers).
-        -- We do know however that the compiler will only configure the
-        -- programs it cares about, and those are the ones we monitor here.
-          monitorFiles (programsMonitorFiles progdb')
-
-          return result
-      where
-        hcFlavor = flagToMaybe projectConfigHcFlavor
-        hcPath   = flagToMaybe projectConfigHcPath
-        hcPkg    = flagToMaybe projectConfigHcPkg
-        progdb   =
-            userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths))
-          . modifyProgramSearchPath
-              (++ [ ProgramSearchPathDir dir
-                  | dir <- fromNubList packageConfigProgramPathExtra ])
-          $ defaultProgramDb
+    phaseConfigureCompiler = configureCompiler verbosity distDirLayout
 
     -- Configuring other programs.
     --
diff --git a/cabal-install/src/Distribution/Client/ScriptUtils.hs b/cabal-install/src/Distribution/Client/ScriptUtils.hs
index 9f012380256..c83b0c07301 100644
--- a/cabal-install/src/Distribution/Client/ScriptUtils.hs
+++ b/cabal-install/src/Distribution/Client/ScriptUtils.hs
@@ -27,13 +27,21 @@ import Distribution.Client.DistDirLayout
     ( DistDirLayout(..) )
 import Distribution.Client.HashValue
     ( hashValue, showHashValue )
+import Distribution.Client.HttpUtils
+         ( HttpTransport, configureTransport )
 import Distribution.Client.NixStyleOptions
     ( NixStyleFlags (..) )
 import Distribution.Client.ProjectConfig
     ( ProjectConfig(..), ProjectConfigShared(..)
-    , parseProjectConfig, reportParseResult, withProjectOrGlobalConfig )
+    , reportParseResult, withProjectOrGlobalConfig
+    , projectConfigHttpTransport )
+import Distribution.Client.ProjectConfig.Legacy
+    ( ProjectConfigSkeleton
+    , parseProjectSkeleton, instantiateProjectConfigSkeleton )
 import Distribution.Client.ProjectFlags
     ( flagIgnoreProject )
+import Distribution.Client.RebuildMonad
+    ( runRebuild )
 import Distribution.Client.Setup
     ( ConfigFlags(..), GlobalFlags(..) )
 import Distribution.Client.TargetSelector
@@ -44,6 +52,8 @@ import Distribution.FieldGrammar
     ( parseFieldGrammar, takeFields )
 import Distribution.Fields
     ( ParseResult, parseFatalFailure, readFields )
+import Distribution.PackageDescription
+    ( ignoreConditions )
 import Distribution.PackageDescription.FieldGrammar
     ( executableFieldGrammar )
 import Distribution.PackageDescription.PrettyPrint
@@ -51,16 +61,20 @@ import Distribution.PackageDescription.PrettyPrint
 import Distribution.Parsec
     ( Position(..) )
 import Distribution.Simple.Flag
-    ( fromFlagOrDefault )
+    ( fromFlagOrDefault, flagToMaybe )
 import Distribution.Simple.PackageDescription
     ( parseString )
 import Distribution.Simple.Setup
     ( Flag(..) )
+import Distribution.Simple.Compiler
+    ( compilerInfo )
 import Distribution.Simple.Utils
     ( createDirectoryIfMissingVerbose, createTempDirectory, die', handleDoesNotExist, readUTF8File, warn, writeUTF8File )
 import qualified Distribution.SPDX.License as SPDX
 import Distribution.Solver.Types.SourcePackage as SP
     ( SourcePackage(..) )
+import Distribution.System
+    ( Platform(..) )
 import Distribution.Types.BuildInfo
     ( BuildInfo(..) )
 import Distribution.Types.CondTree
@@ -73,6 +87,10 @@ import Distribution.Types.PackageDescription
     ( PackageDescription(..), emptyPackageDescription )
 import Distribution.Types.PackageName.Magic
     ( fakePackageCabalFileName, fakePackageId )
+import Distribution.Utils.NubList
+    ( fromNubList )
+import Distribution.Client.ProjectPlanning
+    ( configureCompiler )
 import Distribution.Verbosity
     ( normal )
 import Language.Haskell.Extension
@@ -217,7 +235,17 @@ withContextAndSelectors noTargets kind flags@NixStyleFlags {..} targetStrings gl
 
         scriptContents <- BS.readFile script
         executable     <- readExecutableBlockFromScript verbosity scriptContents
-        projectCfg     <- readProjectBlockFromScript verbosity (takeFileName script) scriptContents
+
+
+        httpTransport <- configureTransport verbosity
+                     (fromNubList . projectConfigProgPathExtra $ projectConfigShared cliConfig)
+                     (flagToMaybe . projectConfigHttpTransport $ projectConfigBuildOnly cliConfig)
+
+        projectCfgSkeleton <- readProjectBlockFromScript verbosity httpTransport (distDirLayout ctx) (takeFileName script) scriptContents
+
+        (compiler, Platform arch os, _) <- runRebuild (distProjectRootDirectory . distDirLayout $ ctx) $ configureCompiler verbosity (distDirLayout ctx) (fst $ ignoreConditions projectCfgSkeleton)
+
+        let projectCfg = instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty projectCfgSkeleton :: ProjectConfig
 
         let executable' = executable & L.buildInfo . L.defaultLanguage %~ maybe (Just Haskell2010) Just
             ctx'        = ctx & lProjectConfig %~ (<> projectCfg)
@@ -312,12 +340,12 @@ readExecutableBlockFromScript verbosity str = do
 -- * @-}@
 --
 -- Return the metadata.
-readProjectBlockFromScript :: Verbosity -> String -> BS.ByteString -> IO ProjectConfig
-readProjectBlockFromScript verbosity scriptName str = do
+readProjectBlockFromScript :: Verbosity -> HttpTransport -> DistDirLayout -> String -> BS.ByteString -> IO ProjectConfigSkeleton
+readProjectBlockFromScript verbosity httpTransport DistDirLayout{distDownloadSrcDirectory} scriptName str = do
     case extractScriptBlock "project" str of
         Left  _ -> return mempty
-        Right x -> reportParseResult verbosity "script" scriptName
-                 $ parseProjectConfig scriptName x
+        Right x ->    reportParseResult verbosity "script" scriptName
+                  =<< parseProjectSkeleton distDownloadSrcDirectory httpTransport verbosity [] scriptName x
 
 -- | Extract the first encountered script metadata block started end
 -- terminated by the tokens

From f812afbc54287c91608f6a105e1369af5cfffb36 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Sat, 26 Mar 2022 12:35:01 -0400
Subject: [PATCH 18/22] fix outstanding merge issue

---
 cabal-install/src/Distribution/Client/ProjectPlanning.hs | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 9ca461b9e6f..24e39695eca 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -405,7 +405,6 @@ configureCompiler verbosity
                              },
                              projectConfigLocalPackages = PackageConfig {
                                packageConfigProgramPaths,
-                               packageConfigProgramArgs,
                                packageConfigProgramPathExtra
                              }
                            } = do
@@ -415,7 +414,6 @@ configureCompiler verbosity
         rerunIfChanged verbosity fileMonitorCompiler
                        (hcFlavor, hcPath, hcPkg, progsearchpath,
                         packageConfigProgramPaths,
-                        packageConfigProgramArgs,
                         packageConfigProgramPathExtra) $ do
 
           liftIO $ info verbosity "Compiler settings changed, reconfiguring..."
@@ -439,7 +437,6 @@ configureCompiler verbosity
         hcPkg    = flagToMaybe projectConfigHcPkg
         progdb   =
             userSpecifyPaths (Map.toList (getMapLast packageConfigProgramPaths))
-          . userSpecifyArgss (Map.toList (getMapMappend packageConfigProgramArgs))
           . modifyProgramSearchPath
               (++ [ ProgramSearchPathDir dir
                   | dir <- fromNubList packageConfigProgramPathExtra ])

From f3c870473643a42b3b5cd92b91ef78227d5f3b9a Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Mon, 28 Mar 2022 18:06:23 -0400
Subject: [PATCH 19/22] use existing config available when checking for
 compiler for package flags

---
 cabal-install/src/Distribution/Client/ProjectPlanning.hs | 2 +-
 cabal-install/src/Distribution/Client/ScriptUtils.hs     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index 24e39695eca..11e011543f8 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -333,7 +333,7 @@ rebuildProjectConfig verbosity
           liftIO $ createDirectoryIfMissingVerbose verbosity True distProjectCacheDirectory
           projectConfigSkeleton <- phaseReadProjectConfig
           -- have to create the cache directory before configuring the compiler
-          (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout (fst $ PD.ignoreConditions projectConfigSkeleton)
+          (compiler, Platform arch os, _) <- configureCompiler verbosity distDirLayout ((fst $ PD.ignoreConditions projectConfigSkeleton) <> cliConfig)
           let projectConfig = instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty projectConfigSkeleton
           localPackages <- phaseReadLocalPackages (projectConfig <> cliConfig)
           return (projectConfig, localPackages)
diff --git a/cabal-install/src/Distribution/Client/ScriptUtils.hs b/cabal-install/src/Distribution/Client/ScriptUtils.hs
index c83b0c07301..6555b92ef7c 100644
--- a/cabal-install/src/Distribution/Client/ScriptUtils.hs
+++ b/cabal-install/src/Distribution/Client/ScriptUtils.hs
@@ -243,7 +243,7 @@ withContextAndSelectors noTargets kind flags@NixStyleFlags {..} targetStrings gl
 
         projectCfgSkeleton <- readProjectBlockFromScript verbosity httpTransport (distDirLayout ctx) (takeFileName script) scriptContents
 
-        (compiler, Platform arch os, _) <- runRebuild (distProjectRootDirectory . distDirLayout $ ctx) $ configureCompiler verbosity (distDirLayout ctx) (fst $ ignoreConditions projectCfgSkeleton)
+        (compiler, Platform arch os, _) <- runRebuild (distProjectRootDirectory . distDirLayout $ ctx) $ configureCompiler verbosity (distDirLayout ctx) ((fst $ ignoreConditions projectCfgSkeleton) <> projectConfig ctx)
 
         let projectCfg = instantiateProjectConfigSkeleton os arch (compilerInfo compiler) mempty projectCfgSkeleton :: ProjectConfig
 

From e70d6f982f355343effe526970b1526141fdfc71 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 30 Mar 2022 18:43:06 -0400
Subject: [PATCH 20/22] review comments

---
 .../src/Distribution/Client/ProjectConfig.hs  |  8 +++----
 .../Client/ProjectConfig/Legacy.hs            | 22 +++++++++----------
 .../ConditionalAndImport/cabal.out            |  3 +++
 .../ConditionalAndImport/cabal.test.hs        |  1 +
 4 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index bb6f07d3b9c..9ca62bd63e7 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -625,12 +625,12 @@ readGlobalConfig verbosity configFileFlag = do
     monitorFiles [monitorFileHashed configFile]
     return (convertLegacyGlobalConfig config)
 
-reportParseResult :: Verbosity -> String -> FilePath -> OldParser.ParseResult a -> IO a
+reportParseResult :: Verbosity -> String -> FilePath -> OldParser.ParseResult ProjectConfigSkeleton -> IO ProjectConfigSkeleton
 reportParseResult verbosity _filetype filename (OldParser.ParseOk warnings x) = do
-    unless (null warnings) $
-      let msg = unlines (map (OldParser.showPWarning filename) warnings)
+   unless (null warnings) $
+      let msg = unlines (map (OldParser.showPWarning (intercalate ", " $ filename : projectSkeletonImports x)) warnings)
        in warn verbosity msg
-    return x
+   return x
 reportParseResult verbosity filetype filename (OldParser.ParseFailed err) =
     let (line, msg) = OldParser.locatedErrorMsg err
      in die' verbosity $ "Error parsing " ++ filetype ++ " " ++ filename
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index adeaf29cb28..2ed03cc6888 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -116,7 +116,7 @@ import Network.URI (URI (..), parseURI)
 import Distribution.Fields.ConfVar (parseConditionConfVarFromClause)
 
 import Distribution.Client.HttpUtils
-import System.FilePath ((</>), isPathSeparator)
+import System.FilePath ((</>), isPathSeparator, makeValid)
 import System.Directory (createDirectoryIfMissing)
 
 
@@ -168,15 +168,15 @@ parseProjectSkeleton cacheDir httpTransport verbosity seenImports source bs = (s
                 rest <- go [] xs
                 pure . fmap mconcat . sequence $ [fs, res, rest]
          (ParseUtils.Section l "if" p xs') -> do
-                           subpcs <- go [] xs'
-                           let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
-                           (elseClauses, rest) <- parseElseClauses xs
-                           let condNode =  (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e]) <$>
-                                  -- we rewrap as as a section so the readFields lexer of the conditional parser doesn't get confused
-                                  adaptParseError l (parseConditionConfVarFromClause . BS.pack $ "if(" <> p <> ")") <*>
-                                  subpcs <*>
-                                  elseClauses
-                           pure . fmap mconcat . sequence $ [fs, condNode, rest]
+                subpcs <- go [] xs'
+                let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig (reverse acc)
+                (elseClauses, rest) <- parseElseClauses xs
+                let condNode =  (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e]) <$>
+                      -- we rewrap as as a section so the readFields lexer of the conditional parser doesn't get confused
+                      adaptParseError l (parseConditionConfVarFromClause . BS.pack $ "if(" <> p <> ")") <*>
+                      subpcs <*>
+                      elseClauses
+                pure . fmap mconcat . sequence $ [fs, condNode, rest]
          _ -> go (x:acc) xs
     go acc [] = pure . fmap singletonProjectConfigSkeleton . fieldsToConfig $ reverse acc
 
@@ -211,7 +211,7 @@ parseProjectSkeleton cacheDir httpTransport verbosity seenImports source bs = (s
     fetchImportConfig :: ProjectConfigImport -> IO BS.ByteString
     fetchImportConfig pci = case parseURI pci of
          Just uri -> do
-            let fp = cacheDir </> map (\x -> if isPathSeparator x then 'X' else x) (show uri) -- TODO can we do better?
+            let fp = cacheDir </> map (\x -> if isPathSeparator x then '_' else x) (makeValid $ show uri)
             createDirectoryIfMissing True cacheDir
             _ <- downloadURI httpTransport verbosity uri fp
             BS.readFile fp
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
index acd94e8947b..e125635e0eb 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
@@ -13,3 +13,6 @@ Warning: The directory <ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/incoming
 # cabal v2-build
 Error: cabal: Error parsing project file <ROOT>/cabal-cyclical.project:3:
 cyclical import of cabal-cyclical.project
+# cabal v2-build
+Error: cabal: Error parsing project file <ROOT>/cabal-bad-conditional.project:
+Cannot set compiler in a conditional clause of a cabal project file
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
index f1f125207e2..0791050f66d 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.test.hs
@@ -3,3 +3,4 @@ main = cabalTest $
   withRepo "repo" $ do
      cabal "v2-run" [ "some-exe" ]
      fails $ cabal "v2-build" [ "--project=cabal-cyclical.project" ]
+     fails $ cabal "v2-build" [ "--project=cabal-bad-conditional.project" ]

From 7525a7d3d821f0b84202bb41726c89ee0242ccd5 Mon Sep 17 00:00:00 2001
From: Gershom Bazerman <gershom@arista.com>
Date: Wed, 30 Mar 2022 22:33:49 -0400
Subject: [PATCH 21/22] add missing test file

---
 .../ConditionalAndImport/cabal-bad-conditional.project        | 4 ++++
 1 file changed, 4 insertions(+)
 create mode 100644 cabal-testsuite/PackageTests/ConditionalAndImport/cabal-bad-conditional.project

diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-bad-conditional.project b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-bad-conditional.project
new file mode 100644
index 00000000000..1cd137e6de7
--- /dev/null
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal-bad-conditional.project
@@ -0,0 +1,4 @@
+packages: .
+
+if(True)
+  compiler: ghc

From 2496a7d77c0e640efe789d711d84e90f5dc640a5 Mon Sep 17 00:00:00 2001
From: gbaz <gershomb@gmail.com>
Date: Thu, 31 Mar 2022 12:00:52 -0400
Subject: [PATCH 22/22] Update pr-7783

---
 changelog.d/pr-7783 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/changelog.d/pr-7783 b/changelog.d/pr-7783
index f15e61fdef2..bbf8cda6f8d 100644
--- a/changelog.d/pr-7783
+++ b/changelog.d/pr-7783
@@ -2,6 +2,7 @@ synopsis: Conditionals and imports in cabal.project files
 packages: cabal-install
 prs: #7783
 issues: #7556
+significance: significant
 
 description: {