Display provenance information when packages are duplicated

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

@@ -471,12 +471,12 @@ resolveTargetSelectors (KnownTargets{knownPackagesPrimary = []}) [] _ =
     ([TargetSelectorNoTargetsInCwd], [])
 
 resolveTargetSelectors (KnownTargets{knownPackagesPrimary}) [] _
-  | [pkgid] <- pkgids =
+  | [(pkgid, _)] <- knownPackages =
     ([], [TargetPackage TargetImplicitCwd [pkgid] Nothing])
   | otherwise =
-    ([TargetSelectorNotSinglePackage pkgids], [])
+    ([TargetSelectorNotSinglePackage knownPackages], [])
   where
-    pkgids = [ pinfoId | KnownPackage{pinfoId} <- knownPackagesPrimary ]
+    knownPackages = [ (pinfoId, pinfoPackageFile) | KnownPackage{pinfoId, pinfoPackageFile} <- knownPackagesPrimary ]
 
 resolveTargetSelectors knowntargets targetStrs mfilter =
     partitionEithers
@@ -596,7 +596,11 @@ data TargetSelectorProblem
    | TargetSelectorUnrecognised String
      -- ^ Syntax error when trying to parse a target string.
    | TargetSelectorNoCurrentPackage TargetString
-   | TargetSelectorNotSinglePackage [PackageId]
+   | TargetSelectorNotSinglePackage [(PackageId, Maybe (FilePath, FilePath))]
+      -- ^ Some PackageIds were duplicated.
+      -- Track them and their provenance if available.
+      -- The tuple is expected to hold an absolute and a relative filepath to
+      -- the respective cabal file.
    | TargetSelectorNoTargetsInCwd
    | TargetSelectorNoTargetsInProject
    | TargetSelectorNoScript TargetString
@@ -812,23 +816,29 @@ reportTargetSelectorProblems verbosity problems = do
       _:_ ->
         die' verbosity noPackageErrorMessage
 
-    case [ pkgids | TargetSelectorNotSinglePackage pkgids <- problems ] of
+    case [ knownPkgs | TargetSelectorNotSinglePackage knownPkgs <- problems ] of
       []      -> return ()
-      mpkgids ->
+      mknownPkgs ->
         let
-          allpkgids = concat mpkgids
+          allknownPkgs = concat mknownPkgs
         in
-          case allpkgids of
+          case allknownPkgs of
             [] ->
               die' verbosity noPackageErrorMessage
             pkgids ->
               die' verbosity $
-                  "Multiple packages have been found:\n  "
-               ++ unlines (map prettyShow pkgids)
-
+                  "Multiple packages have been found:\n"
+               ++ unlines (
+                    map
+                      (uncurry prettyAmbiguousPackageProvenance)
+                      pkgids)
 
         where
-
+          prettyAmbiguousPackageProvenance :: PackageId -> Maybe (FilePath, FilePath) -> String
+          prettyAmbiguousPackageProvenance pkgid provenance =
+            prettyShow pkgid ++ (case provenance of
+              Nothing -> mempty
+              Just (_, relativeCabalFile) -> " defined in: " ++ relativeCabalFile)
 
     case [ t | TargetSelectorNoScript t <- problems ] of
       []  -> return ()
@@ -1752,7 +1762,9 @@ data KnownPackage =
      KnownPackage {
        pinfoId          :: PackageId,
        pinfoDirectory   :: Maybe (FilePath, FilePath),
+       -- ^ Absolute path and relative path of the root directory of this package.
        pinfoPackageFile :: Maybe (FilePath, FilePath),
+       -- ^ Absolute path and relative path to the .cabal file of this package.
        pinfoComponents  :: [KnownComponent]
      }
    | KnownPackageName {
@@ -1828,12 +1840,12 @@ collectKnownPackageInfo dirActions@DirActions{..}
     (pkgdir, pkgfile) <-
       case loc of
         --TODO: local tarballs, remote tarballs etc
-        LocalUnpackedPackage dir _cabalFile -> do
+        LocalUnpackedPackage dir cabalFile -> do
           dirabs <- canonicalizePath dir
           dirrel <- makeRelativeToCwd dirActions dirabs
           --TODO: ought to get this earlier in project reading
-          let fileabs = dirabs </> prettyShow (packageName pkg) <.> "cabal"
-              filerel = dirrel </> prettyShow (packageName pkg) <.> "cabal"
+          let fileabs = dirabs </> fromMaybe (prettyShow (packageName pkg) <.> "cabal") cabalFile
+              filerel = dirrel </> fromMaybe (prettyShow (packageName pkg) <.> "cabal") cabalFile
           exists <- doesFileExist fileabs
           return ( Just (dirabs, dirrel)
                  , if exists then Just (fileabs, filerel) else Nothing