--moduleoverride:mod1:mod2:prefix: generalized patchFile to allow non-global effect; works on cmdline / config

compiler/commands.nim

@@ -931,6 +931,24 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
     else: conf.spellSuggestMax = parseInt(arg)
   of "declaredlocs":
     processOnOffSwitchG(conf, {optDeclaredLocs}, arg, pass, info)
+  of "moduleoverride":
+    # --moduleoverride:std/sequtils:pkg/foo/sequtils2:prefix1,prefix2/sub
+    proc validate(path: string): string =
+      if path.isAbsolute or path.isCanonicalPath: result = path
+      else: localError(conf, info, "module path must be canonical or absolute, got: $1" % path)
+    let args = arg.split(":")
+    if args.len notin {2, 3}:
+      localError(conf, info, "invalid arg: $1" % arg)
+    else:
+      let lhs = args[0].validate
+      let rhs = args[1].validate
+      if args.len == 2:
+        conf.localOverrides.add LocalOverride(lhs: lhs, rhs: rhs, prefix: "/")
+      elif args.len == 3:
+        let prefixes = args[2].split(",")
+        for a in prefixes:
+          let prefix = a.validate
+          conf.localOverrides.add LocalOverride(lhs: lhs, rhs: rhs, prefix: prefix)
   of "dynliboverride":
     dynlibOverride(conf, switch, arg, pass, info)
   of "dynliboverrideall":

compiler/options.nim

@@ -278,7 +278,12 @@ type
     foLegacyRelProj # legacy, shortest of (foAbs, foRelProject)
     foName # lastPathPart, e.g.: foo.nim
     foStacktrace # if optExcessiveStackTrace: foAbs else: foName
+  LocalOverrideAtom* = object
 
+  LocalOverride* = object
+    lhs*: string
+    rhs*: string
+    prefix*: string
   ConfigRef* {.acyclic.} = ref object ## every global configuration
                           ## fields marked with '*' are subject to
                           ## the incremental compilation mechanisms
@@ -344,6 +349,7 @@ type
     jsonBuildFile*: AbsoluteFile
     prefixDir*, libpath*, nimcacheDir*: AbsoluteDir
     dllOverrides, moduleOverrides*, cfileSpecificOptions*: StringTableRef
+    localOverrides*: seq[LocalOverride]
     projectName*: string # holds a name like 'nim'
     projectPath*: AbsoluteDir # holds a path like /home/alice/projects/nim/compiler/
     projectFull*: AbsoluteFile # projectPath/projectName
@@ -823,6 +829,12 @@ const stdlibDirs = [
 const
   pkgPrefix = "pkg/"
   stdPrefix = "std/"
+  systemPrefix = "system/"
+
+proc isCanonicalPath*(path: string): bool =
+  # in future work we can support also `this/` for current package.
+  let path = path & '/'
+  result = path.startsWith(stdPrefix) or path.startsWith(systemPrefix) or path.startsWith(pkgPrefix)
 
 proc getRelativePathFromConfigPath*(conf: ConfigRef; f: AbsoluteFile, isTitle = false): RelativeFile =
   let f = $f
@@ -852,7 +864,24 @@ proc findFile*(conf: ConfigRef; f: string; suppressStdlib = false): AbsoluteFile
           result = rawFindFile2(conf, RelativeFile f.toLowerAscii)
   patchModule(conf)
 
-proc findModule*(conf: ConfigRef; modulename, currentModule: string): AbsoluteFile =
+proc canonicalImport*(conf: ConfigRef, file: AbsoluteFile): string
+
+proc canonicalImportPkg*(conf: ConfigRef, file: AbsoluteFile): string =
+  result = canonicalImport(conf, file)
+  let tmp = result & '/'
+  if not (tmp.startsWith(stdPrefix) or tmp.startsWith(systemPrefix)):
+    result = pkgPrefix & result
+
+proc pathMatchesPrefix(conf: ConfigRef, path: string, prefix: string): bool =
+  # see also `prefixmatches.prefixMatch`
+  if prefix == "/": result = true
+  elif prefix.isAbsolute:
+    result = path.isRelativeTo(prefix)
+  else: # canonical, eg std/foo or pkg/fusion/bar
+    let canon = canonicalImportPkg(conf, AbsoluteFile(path)) & '/'
+    result = canon.startsWith(prefix & '/')
+
+proc findModule*(conf: ConfigRef; modulename, currentModule: string, depth = 0): AbsoluteFile =
   # returns path to module
   var m = addFileExt(modulename, NimExt)
   if m.startsWith(pkgPrefix):
@@ -870,6 +899,19 @@ proc findModule*(conf: ConfigRef; modulename, currentModule: string): AbsoluteFi
       result = AbsoluteFile currentPath / m
     if not fileExists(result):
       result = findFile(conf, m)
+  if not result.isEmpty:
+    let canon = canonicalImportPkg(conf, result)
+    for ai in conf.localOverrides:
+      if ai.lhs == canon:
+        if pathMatchesPrefix(conf, currentModule, ai.prefix):
+          if depth > 10:
+            # can happen with: `--moduleoverride:std/foo2:std/foo2` or `--moduleoverride:std/foo2:/pathto/std/foo2`
+            # or more complex cases with cycles. Future work could improve things but this is a rare edge case.
+            # `localError` not defined in scope, alternative is some simple refactoring.
+            stderr.write "module resolution too deep, possible cyclic overrides detected\n"
+            return AbsoluteFile""
+          result = findModule(conf, ai.rhs, currentModule, depth + 1)
+          break
   patchModule(conf)
 
 proc findProjectNimFile*(conf: ConfigRef; pkg: string): string =

tests/misc/trunner.nim

@@ -377,4 +377,69 @@ mused3.nim(75, 10) Hint: duplicate import of 'mused3a'; previous import here: mu
 """
 
 else:
+  block: # moduleoverride
+    proc fn(opt: string, expected: string) =
+      let output = runNimCmdChk("nimble/mmoduleoverride.nim", fmt"--warnings:off --hints:off {opt}")
+      doAssert output == expected, opt & "\noutput:\n" & output & "expected:\n" & expected
+    fn(""): """
+in pkgA.module2
+in pkgC.module2
+in pkgB.module2
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b"): """
+in pkgA.module2
+in pkgC.module2b
+in pkgB.module2
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:pkg/pkgA"): """
+in pkgA.module2
+in pkgC.module2b
+in pkgB.module2
+in pkgC.module2
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:pkg/pkgB"): """
+in pkgA.module2
+in pkgC.module2
+in pkgB.module2
+in pkgC.module2b
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:pkg"): """
+in pkgA.module2
+in pkgC.module2b
+in pkgB.module2
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:pkg/pkgA/module2"): """
+in pkgA.module2
+in pkgC.module2b
+in pkgB.module2
+in pkgC.module2
+"""
+    fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:pkg/pkgA/module"): """
+in pkgA.module2
+in pkgC.module2
+in pkgB.module2
+"""
+    fn("--moduleoverride:std/strutils:pkg/pkgC/module2b"): """
+in pkgC.module2b
+in pkgA.module2
+in pkgC.module2
+in pkgB.module2
+"""
+    let path = testsDir / "nimble/nimbleDir/simplePkgs/pkgA-0.1.0/pkgA/module2.nim"
+    fn(fmt"--moduleoverride:pkg/pkgC/module2:pkg/pkgC/module2b:{path}"): """
+in pkgA.module2
+in pkgC.module2b
+in pkgB.module2
+in pkgC.module2
+"""
+    # edge case, whether to consider `pkg/tests/nimble/mmoduleoverride` as canonical
+    fn("--moduleoverride:std/strutils:pkg/pkgC/module2b:pkg/tests/nimble/mmoduleoverride"): """
+in pkgC.module2b
+in pkgA.module2
+in pkgC.module2
+in pkgB.module2
+"""
+    doAssertRaises(AssertionDefect): fn("--moduleoverride:pkgC/module2:pkg/pkgC/module2b:pkg/pkgA/module", "") # pkg/ missing
+    doAssertRaises(AssertionDefect): fn("--moduleoverride:pkg/pkgC/module2:pkg/pkgC/nonexistent", "") # pkg/pkgC/nonexistent is nonexistent
+
   discard # only during debugging, tests added here will run with `-d:nimTestsTrunnerDebugging` enabled

tests/nimble/mmoduleoverride.nim

@@ -0,0 +1,8 @@
+discard """
+  matrix: "--moduleoverride:pkgC/module2:std/foo2b:$nim_prs_D/lib/"
+  # matrix: "--moduleoverride:std/foo2:std/foo2b:$nim_prs_D/lib/"
+"""
+import std/strutils
+import pkgA/module2 as A
+import pkgB/module2 as B
+import pkgC/module2 as C

tests/nimble/mmoduleoverride.nims

@@ -0,0 +1,5 @@
+switch("clearNimblePath")
+switch("nimblePath", "$projectdir/nimbleDir/simplePkgs")
+switch("path", "$nimblepath/pkgA-0.1.0")
+switch("path", "$nimblepath/pkgB-#head")
+switch("path", "$nimblepath/pkgC-#head")

tests/nimble/nimbleDir/simplePkgs/pkgA-0.1.0/pkgA/module2.nim

@@ -0,0 +1,2 @@
+static: echo "in pkgA.module2"
+import pkgC/module2

tests/nimble/nimbleDir/simplePkgs/pkgB-#head/pkgB/module2.nim

@@ -0,0 +1,2 @@
+static: echo "in pkgB.module2"
+import pkgC/module2

tests/nimble/nimbleDir/simplePkgs/pkgC-#head/pkgC/module2.nim

@@ -0,0 +1 @@
+static: echo "in pkgC.module2"

tests/nimble/nimbleDir/simplePkgs/pkgC-#head/pkgC/module2b.nim

@@ -0,0 +1 @@
+static: echo "in pkgC.module2b"