Improve error message when multiple .cabal files are in the same directory

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

@@ -300,6 +300,12 @@ renderTargetProblem verb _ (TargetProblemNoSuchComponent pkgid cname) =
   ++ "for the project plan, which would suggest an inconsistency "
   ++ "between readTargetSelectors and resolveTargets."
 
+renderTargetProblem verb _ (TargetProblemNotSinglePackage []) =
+    "Internal error when trying to " ++ verb ++ ". Found no package."
+renderTargetProblem verb _ (TargetProblemNotSinglePackage pkgids) =
+    "Internal error when trying to " ++ verb ++ ". Found multiple packages:\n"
+  ++ unlines (map prettyShow pkgids)
+
 
 ------------------------------------------------------------
 -- Rendering error messages for TargetProblemNoneEnabled

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

@@ -220,7 +220,7 @@ packageToSdist :: Verbosity -> FilePath -> OutputFormat -> FilePath -> Unresolve
 packageToSdist verbosity projectRootDir format outputFile pkg = do
     let death = die' verbosity ("The impossible happened: a local package isn't local" <> (show pkg))
     dir0 <- case srcpkgSource pkg of
-             LocalUnpackedPackage path             -> pure (Right path)
+             LocalUnpackedPackage path _           -> pure (Right path)
              RemoteSourceRepoPackage _ (Just tgz)  -> pure (Left tgz)
              RemoteSourceRepoPackage {}            -> death
              LocalTarballPackage tgz               -> pure (Left tgz)

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

@@ -131,7 +131,7 @@ configure verbosity packageDBs repoCtxt comp platform progdb
      let installPlan = InstallPlan.configureInstallPlan configFlags installPlan0
      in case fst (InstallPlan.ready installPlan) of
       [pkg@(ReadyPackage
-              (ConfiguredPackage _ (SourcePackage _ _ (LocalUnpackedPackage _) _)
+              (ConfiguredPackage _ (SourcePackage _ _ (LocalUnpackedPackage _ _) _)
                                  _ _ _))] -> do
         configurePackage verbosity
           platform (compilerInfo comp)
@@ -298,7 +298,7 @@ planLocalPackage verbosity comp platform configFlags configExFlags
       localPkg = SourcePackage {
         srcpkgPackageId          = packageId pkg,
         srcpkgDescription        = pkg,
-        srcpkgSource             = LocalUnpackedPackage ".",
+        srcpkgSource             = LocalUnpackedPackage "." Nothing,
         srcpkgDescrOverride      = Nothing
       }
 

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

@@ -216,7 +216,7 @@ checkTarget verbosity target = case target of
 
 fetchPackage :: Verbosity -> RepoContext -> PackageLocation a -> IO ()
 fetchPackage verbosity repoCtxt pkgsrc = case pkgsrc of
-    LocalUnpackedPackage _dir  -> return ()
+    LocalUnpackedPackage _dir _cabalFile -> return ()
     LocalTarballPackage  _file -> return ()
 
     RemoteTarballPackage _uri _ ->

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

@@ -77,7 +77,7 @@ import qualified Hackage.Security.Client as Sec
 --
 isFetched :: UnresolvedPkgLoc -> IO Bool
 isFetched loc = case loc of
-    LocalUnpackedPackage _dir       -> return True
+    LocalUnpackedPackage _dir _     -> return True
     LocalTarballPackage  _file      -> return True
     RemoteTarballPackage _uri local -> return (isJust local)
     RepoTarballPackage repo pkgid _ -> doesFileExist (packageFile repo pkgid)
@@ -91,8 +91,8 @@ isFetched loc = case loc of
 checkFetched :: UnresolvedPkgLoc
              -> IO (Maybe ResolvedPkgLoc)
 checkFetched loc = case loc of
-    LocalUnpackedPackage dir  ->
-      return (Just $ LocalUnpackedPackage dir)
+    LocalUnpackedPackage dir cabalFile ->
+      return (Just $ LocalUnpackedPackage dir cabalFile)
     LocalTarballPackage  file ->
       return (Just $ LocalTarballPackage  file)
     RemoteTarballPackage uri (Just file) ->
@@ -126,8 +126,8 @@ fetchPackage :: Verbosity
              -> UnresolvedPkgLoc
              -> IO ResolvedPkgLoc
 fetchPackage verbosity repoCtxt loc = case loc of
-    LocalUnpackedPackage dir  ->
-      return (LocalUnpackedPackage dir)
+    LocalUnpackedPackage dir cabalFile ->
+      return (LocalUnpackedPackage dir cabalFile)
     LocalTarballPackage  file ->
       return (LocalTarballPackage  file)
     RemoteTarballPackage uri (Just file) ->

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

@@ -152,7 +152,7 @@ get verbosity repoCtxt _ getFlags userTargets = do
             die' verbosity $ "The 'get' command does no yet support targets "
                           ++ "that are remote source repositories."
 
-          LocalUnpackedPackage _ ->
+          LocalUnpackedPackage _ _ ->
             error "Distribution.Client.Get.unpack: the impossible happened."
       where
         usePristine :: Bool

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

@@ -378,7 +378,7 @@ readRepoIndex verbosity repoCtxt repo idxState =
       , srcpkgDescription = pkgdesc
       , srcpkgSource      = case pkgEntry of
           NormalPackage _ _ _ _       -> RepoTarballPackage repo pkgid Nothing
-          BuildTreeRef  _  _ _ path _ -> LocalUnpackedPackage path
+          BuildTreeRef  _  _ _ path _ -> LocalUnpackedPackage path Nothing
       , srcpkgDescrOverride = case pkgEntry of
           NormalPackage _ _ pkgtxt _ -> Just pkgtxt
           _                          -> Nothing

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

@@ -1229,7 +1229,7 @@ installLocalPackage verbosity pkgid location distPref installPkg =
 
   case location of
 
-    LocalUnpackedPackage dir ->
+    LocalUnpackedPackage dir _cabalFile ->
       installPkg (Just dir)
 
     RemoteSourceRepoPackage _repo dir ->

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

@@ -195,7 +195,7 @@ rebuildTargetsDryRun distDirLayout@DistDirLayout{..} shared =
       case mloc of
         Nothing -> return BuildStatusDownload
 
-        Just (LocalUnpackedPackage srcdir) ->
+        Just (LocalUnpackedPackage srcdir _) ->
           -- For the case of a user-managed local dir, irrespective of the
           -- build style, we build from that directory and put build
           -- artifacts under the shared dist directory.

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

@@ -651,7 +651,17 @@ reportParseResult verbosity filetype filename (OldParser.ParseFailed err) =
 --
 data ProjectPackageLocation =
      ProjectPackageLocalCabalFile FilePath
-   | ProjectPackageLocalDirectory FilePath FilePath -- dir and .cabal file
+   | ProjectPackageLocalDirectory FilePath FilePath
+     -- ^ In @'ProjectPackageLocalDirectory' directory cabalFile@, @directory@
+     -- is expected to be a filepath relative to the root of the
+     -- project. Similarly, @cabalFile@ is also relative to the root of
+     -- of the project.
+     --
+     -- Consequentially, the following should hold:
+     --
+     -- > takeDirectory cabalFile == directory
+     -- > directory </> takeFileName cabalFile == cabalFile
+     --
    | ProjectPackageLocalTarball   FilePath
    | ProjectPackageRemoteTarball  URI
    | ProjectPackageRemoteRepo     SourceRepoList
@@ -1041,7 +1051,10 @@ readSourcePackageLocalDirectory
 readSourcePackageLocalDirectory verbosity dir cabalFile = do
     monitorFiles [monitorFileHashed cabalFile]
     root <- askRoot
-    let location = LocalUnpackedPackage (root </> dir)
+    -- cabalFile is not required to be just the filename, but might be
+    -- relative to the project root.
+    let cabalFileName = takeFileName cabalFile
+    let location = LocalUnpackedPackage (root </> dir) (Just cabalFileName)
     liftIO $ fmap (mkSpecificSourcePackage location)
            . readSourcePackageCabalFile verbosity cabalFile
          =<< BS.readFile (root </> cabalFile)

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

@@ -583,12 +583,7 @@ resolveTargets selectPackageTargets selectComponentTarget
       = Left (TargetProblemNoSuchPackage pkgid)
 
     checkTarget (TargetPackage _ pkgids _)
-      = error ("TODO: add support for multiple packages in a directory.  Got\n"
-              ++ unlines (map prettyShow pkgids))
-      -- For the moment this error cannot happen here, because it gets
-      -- detected when the package config is being constructed. This case
-      -- will need handling properly when we do add support.
-      --
+      = Left (TargetProblemNotSinglePackage pkgids)
       -- TODO: how should this use case play together with the
       -- '--cabal-file' option of 'configure' which allows using multiple
       -- .cabal files for a single package?

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

@@ -195,7 +195,7 @@ encodePlanAsJson distDirLayout elaboratedInstallPlan elaboratedSharedConfig =
       packageLocationToJ :: PackageLocation (Maybe FilePath) -> J.Value
       packageLocationToJ pkgloc =
         case pkgloc of
-          LocalUnpackedPackage local ->
+          LocalUnpackedPackage local _cabalFile ->
             J.object [ "type" J..= J.String "local"
                      , "path" J..= J.String local
                      ]

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

@@ -2096,8 +2096,8 @@ elaborateInstallPlan verbosity platform compiler compilerprogdb pkgConfigDB
 shouldBeLocal :: PackageSpecifier (SourcePackage (PackageLocation loc)) -> Maybe PackageId
 shouldBeLocal NamedPackage{}              = Nothing
 shouldBeLocal (SpecificSourcePackage pkg) = case srcpkgSource pkg of
-    LocalUnpackedPackage _ -> Just (packageId pkg)
-    _                      -> Nothing
+    LocalUnpackedPackage _ _ -> Just (packageId pkg)
+    _                        -> Nothing
 
 -- | Given a 'ElaboratedPlanPackage', report if it matches a 'ComponentName'.
 matchPlanPkg :: (ComponentName -> Bool) -> ElaboratedPlanPackage -> Bool

cabal-install/src/Distribution/Client/ProjectPlanning/Types.hs

@@ -446,7 +446,7 @@ dataDirEnvVarForPackage distDirLayout pkg =
        , Just $ srcPath (elabPkgSourceLocation pkg)
             </> dataDir (elabPkgDescription pkg))
   where
-    srcPath (LocalUnpackedPackage path) = path
+    srcPath (LocalUnpackedPackage path _cabalFile) = path
     srcPath (LocalTarballPackage _path) = unpackedPath
     srcPath (RemoteTarballPackage _uri _localTar) = unpackedPath
     srcPath (RepoTarballPackage _repo _packageId _localTar) = unpackedPath

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

@@ -389,7 +389,7 @@ fakeProjectSourcePackage projectRoot = sourcePackage
     sourcePackage = SourcePackage
       { srcpkgPackageId     = fakePackageId
       , srcpkgDescription   = genericPackageDescription
-      , srcpkgSource        = LocalUnpackedPackage projectRoot
+      , srcpkgSource        = LocalUnpackedPackage projectRoot Nothing
       , srcpkgDescrOverride = Nothing
       }
     genericPackageDescription = emptyGenericPackageDescription

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

@@ -44,6 +44,7 @@ data TargetProblem a
     -- directly then of course it can.
     | TargetProblemNoSuchPackage           PackageId
     | TargetProblemNoSuchComponent         PackageId ComponentName
+    | TargetProblemNotSinglePackage        [PackageId]
 
       -- | A custom target problem
     | CustomTargetProblem a

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

@@ -471,10 +471,13 @@ resolveTargetSelectors (KnownTargets{knownPackagesAll = []}) [] _ =
 resolveTargetSelectors (KnownTargets{knownPackagesPrimary = []}) [] ckf =
     ([TargetSelectorNoTargetsInCwd (ckf /= Just ExeKind) ], [])
 
-resolveTargetSelectors (KnownTargets{knownPackagesPrimary}) [] _ =
-    ([], [TargetPackage TargetImplicitCwd pkgids Nothing])
+resolveTargetSelectors (KnownTargets{knownPackagesPrimary}) [] _
+  | [(pkgid, _)] <- knownPackages =
+    ([], [TargetPackage TargetImplicitCwd [pkgid] Nothing])
+  | otherwise =
+    ([TargetSelectorNotSinglePackage knownPackages], [])
   where
-    pkgids = [ pinfoId | KnownPackage{pinfoId} <- knownPackagesPrimary ]
+    knownPackages = [ (pinfoId, pinfoPackageFile) | KnownPackage{pinfoId, pinfoPackageFile} <- knownPackagesPrimary ]
 
 resolveTargetSelectors knowntargets targetStrs mfilter =
     partitionEithers
@@ -594,6 +597,11 @@ data TargetSelectorProblem
    | TargetSelectorUnrecognised String
      -- ^ Syntax error when trying to parse a target string.
    | TargetSelectorNoCurrentPackage TargetString
+   | 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 Bool
      -- ^ bool that flags when it is acceptable to suggest "all" as a target
    | TargetSelectorNoTargetsInProject
@@ -816,7 +824,29 @@ reportTargetSelectorProblems verbosity problems = do
     case [ () | TargetSelectorNoTargetsInProject <- problems ] of
       []  -> return ()
       _:_ ->
+        die' verbosity noPackageErrorMessage
+
+    case [ knownPkgs | TargetSelectorNotSinglePackage knownPkgs <- problems ] of
+      []      -> return ()
+      mknownPkgs -> case concat mknownPkgs of
+        [] ->
+          die' verbosity noPackageErrorMessage
+        pkgids ->
+          die' verbosity $
+               "Multiple packages have been found:\n"
+            ++ unlines ( map (uncurry prettyAmbiguousPackageProvenance) pkgids)
+
+    case [ t | TargetSelectorNoScript t <- problems ] of
+      []  -> return ()
+      target:_ ->
         die' verbosity $
+            "The script '" ++ showTargetString target ++ "' does not exist, "
+         ++ "and only script targets may contain whitespace characters or end "
+         ++ "with ':'"
+
+    fail "reportTargetSelectorProblems: internal error"
+  where
+    noPackageErrorMessage =
             "There is no <pkgname>.cabal package file or cabal.project file. "
          ++ "To build packages locally you need at minimum a <pkgname>.cabal "
          ++ "file. You can use 'cabal init' to create one.\n"
@@ -826,15 +856,12 @@ reportTargetSelectorProblems verbosity problems = do
          ++ "packages in your project and all other build configuration. "
          ++ "See the Cabal user guide for full details."
 
-    case [ t | TargetSelectorNoScript t <- problems ] of
-      []  -> return ()
-      target:_ ->
-        die' verbosity $
-            "The script '" ++ showTargetString target ++ "' does not exist, "
-         ++ "and only script targets may contain whitespace characters or end "
-         ++ "with ':'"
 
-    fail "reportTargetSelectorProblems: internal error"
+    prettyAmbiguousPackageProvenance :: PackageId -> Maybe (FilePath, FilePath) -> String
+    prettyAmbiguousPackageProvenance pkgid provenance =
+      prettyShow pkgid ++ (case provenance of
+        Nothing -> mempty
+        Just (_, relativeCabalFile) -> " defined in: " ++ relativeCabalFile)
 
 
 ----------------------------------
@@ -1738,7 +1765,9 @@ 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 {
@@ -1814,12 +1843,12 @@ collectKnownPackageInfo dirActions@DirActions{..}
     (pkgdir, pkgfile) <-
       case loc of
         --TODO: local tarballs, remote tarballs etc
-        LocalUnpackedPackage dir -> 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

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

@@ -93,7 +93,7 @@ import qualified Data.ByteString.Lazy as BS
 import qualified Distribution.Client.GZipUtils as GZipUtils
 import qualified Distribution.Compat.CharParsing as P
 import System.FilePath
-         ( takeExtension, dropExtension, takeDirectory, splitPath )
+         ( takeExtension, dropExtension, takeDirectory, splitPath, takeFileName )
 import System.Directory
          ( doesFileExist, doesDirectoryExist )
 import Network.URI
@@ -348,12 +348,12 @@ expandUserTarget verbosity userTarget = case userTarget of
       in  return [PackageTargetNamedFuzzy name props userTarget]
 
     UserTargetLocalDir dir ->
-      return [ PackageTargetLocation (LocalUnpackedPackage dir) ]
+      return [ PackageTargetLocation (LocalUnpackedPackage dir Nothing) ]
 
     UserTargetLocalCabalFile file -> do
       let dir = takeDirectory file
       _   <- tryFindPackageDesc verbosity dir (localPackageError dir) -- just as a check
-      return [ PackageTargetLocation (LocalUnpackedPackage dir) ]
+      return [ PackageTargetLocation (LocalUnpackedPackage dir (Just $ takeFileName file)) ]
 
     UserTargetLocalTarball tarballFile ->
       return [ PackageTargetLocation (LocalTarballPackage tarballFile) ]
@@ -392,7 +392,7 @@ readPackageTarget verbosity = traverse modifyLocation
     modifyLocation :: ResolvedPkgLoc -> IO UnresolvedSourcePackage
     modifyLocation location = case location of
 
-      LocalUnpackedPackage dir -> do
+      LocalUnpackedPackage dir _cabalFile -> do
         pkg <- tryFindPackageDesc verbosity dir (localPackageError dir) >>=
                  readGenericPackageDescription verbosity
         return SourcePackage

cabal-install/src/Distribution/Client/Types/PackageLocation.hs

@@ -24,8 +24,15 @@ type ResolvedPkgLoc = PackageLocation FilePath
 
 data PackageLocation local =
 
-    -- | An unpacked package in the given dir, or current dir
-    LocalUnpackedPackage FilePath
+    -- | An unpacked package in the given directory.
+    -- @'LocalUnpackedPackage' directory mCabalFile@, where @directory@ is an
+    -- absolute filepath which points to the root of the *package*.
+    -- I.e., the filepath points to the directory where the '.cabal' file of
+    -- this package can be found.
+    -- If @mCabalFile@ is 'Nothing', then the '.cabal' file can be assumed to
+    -- be '<package-name>.cabal'.
+    -- Otherwise, @mCabalFile@ points to the '.cabal' file within @directory@.
+    LocalUnpackedPackage FilePath (Maybe FilePath)
 
     -- | A package as a tarball that's available as a local tarball
   | LocalTarballPackage FilePath

cabal-install/tests/IntegrationTests2.hs

@@ -468,7 +468,7 @@ testTargetSelectorAmbiguous reportSubCase = do
     mkpkgAt pkgidstr exes loc =
       SourcePackage {
         srcpkgPackageId = pkgid,
-        srcpkgSource = LocalUnpackedPackage loc,
+        srcpkgSource = LocalUnpackedPackage loc Nothing,
         srcpkgDescrOverride  = Nothing,
         srcpkgDescription = GenericPackageDescription {
           packageDescription = emptyPackageDescription { package = pkgid },

cabal-install/tests/UnitTests/Distribution/Client/FetchUtils.hs

@@ -60,10 +60,10 @@ testEmpty = do
 testPassLocalPackage :: Assertion
 testPassLocalPackage = do
   let repoCtxt = error "repoCtxt undefined"
-      loc = LocalUnpackedPackage "a"
+      loc = LocalUnpackedPackage "a" Nothing
   res <- asyncFetchPackages verbosity repoCtxt [loc] $ \downloadMap ->
     waitAsyncFetchPackage verbosity downloadMap loc
-  res @?= LocalUnpackedPackage "a"
+  res @?= LocalUnpackedPackage "a" Nothing
 
 testHttp :: Assertion
 testHttp = withFakeRepoCtxt get200 $ \repoCtxt repo -> do

cabal-testsuite/PackageTests/Ambiguity/multiple-cabal-files/Main.hs

@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"

cabal-testsuite/PackageTests/Ambiguity/multiple-cabal-files/cabal.project

@@ -0,0 +1 @@
+packages: multiple-cabal-files.cabal multiple-cabal-files2.cabal