unbreak cabal haddock --disable-documentation

cabal-install/src/Distribution/Client/CmdHaddock.hs

@@ -143,7 +143,8 @@ haddockAction flags@NixStyleFlags {..} targetStrings globalFlags = do
     runProjectPostBuildPhase verbosity baseCtx buildCtx' buildOutcomes
   where
     verbosity = fromFlagOrDefault normal (configVerbosity configFlags)
-    flags' = flags { installFlags = installFlags { installDocumentation = Flag True } }
+    installDoc = fromFlagOrDefault True (installDocumentation installFlags)
+    flags' = flags { installFlags = installFlags { installDocumentation = Flag installDoc } }
     cliConfig = commandLineFlagsToProjectConfig globalFlags flags' mempty -- ClientInstallFlags, not needed here
 
 -- | This defines what a 'TargetSelector' means for the @haddock@ command.

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/B/B.cabal

@@ -0,0 +1,12 @@
+cabal-version:      2.4
+name:               B
+version:            0.1.0.0
+author:             Artem Pelenitsyn
+maintainer:         a.pelenitsyn@gmail.com
+
+library
+    exposed-modules:  B
+    build-depends:    base
+                    , A
+    hs-source-dirs:   .
+    default-language: Haskell2010

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/B/B.hs

@@ -0,0 +1,8 @@
+-- | Module using external dependency and mentioning it in haddocks
+module B (b) where
+
+import A
+
+-- | Use 'a'
+b :: Int
+b = a

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/cabal.out

@@ -0,0 +1,16 @@
+# cabal v2-update
+Downloading the latest package list from test-local-repo
+# cabal haddock
+Resolving dependencies...
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following will be built:
+ - A-0.1.0.0 (lib) (requires build)
+ - B-0.1.0.0 (lib) (first run)
+Configuring library for A-0.1.0.0..
+Preprocessing library for A-0.1.0.0..
+Building library for A-0.1.0.0..
+Installing library in <PATH>
+Configuring library for B-0.1.0.0..
+Preprocessing library for B-0.1.0.0..
+Running Haddock on library for B-0.1.0.0..
+Documentation created: <ROOT>/cabal.dist/work/dist/build/<ARCH>/ghc-<GHCVER>/B-0.1.0.0/doc/html/B/index.html

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/cabal.project

@@ -0,0 +1 @@
+packages: B

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/cabal.test.hs

@@ -0,0 +1,6 @@
+import Test.Cabal.Prelude
+-- Test that `cabal haddock --disable-documention` works as expected and leads
+-- to a warning if a local package makes an outer reference.
+main = cabalTest . withRepo "repo" $ do
+    r <- cabal' "haddock" ["--disable-documentation", "B"]
+    assertOutputContains "Warning: B: could not find link destinations for" r

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/repo/A-0.1.0.0/A.cabal

@@ -0,0 +1,11 @@
+cabal-version:      2.4
+name:               A
+version:            0.1.0.0
+author:             Artem Pelenitsyn
+maintainer:         a.pelenitsyn@gmail.com
+
+library
+    exposed-modules:  A
+    build-depends:    base
+    hs-source-dirs:   .
+    default-language: Haskell2010

cabal-testsuite/PackageTests/NewHaddock/DisableDoc/repo/A-0.1.0.0/A.hs

@@ -0,0 +1,4 @@
+module A (a) where
+
+a :: Int
+a = 42