Add check on project root file and fail if broken link (#10103)

* Add ProjectRootUsability datatype

* Make findProjectRoot aware of broken files

* Add changelog entry

* Fix typos

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

@@ -3,6 +3,7 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE TypeApplications #-}
 
 -- | Handling project configuration.
 module Distribution.Client.ProjectConfig
@@ -18,8 +19,10 @@ module Distribution.Client.ProjectConfig
 
     -- * Project root
   , findProjectRoot
+  , getProjectRootUsability
   , ProjectRoot (..)
-  , BadProjectRoot
+  , BadProjectRoot (..)
+  , ProjectRootUsability (..)
 
     -- * Project config files
   , readProjectConfig
@@ -196,6 +199,7 @@ import qualified Codec.Archive.Tar.Entry as Tar
 import qualified Distribution.Client.GZipUtils as GZipUtils
 import qualified Distribution.Client.Tar as Tar
 
+import Control.Exception (handle)
 import Control.Monad.Trans (liftIO)
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Lazy as LBS
@@ -215,9 +219,11 @@ import System.Directory
   ( canonicalizePath
   , doesDirectoryExist
   , doesFileExist
+  , doesPathExist
   , getCurrentDirectory
   , getDirectoryContents
   , getHomeDirectory
+  , pathIsSymbolicLink
   )
 import System.FilePath hiding (combine)
 import System.IO
@@ -529,6 +535,24 @@ resolveBuildTimeSettings
 -- Reading and writing project config files
 --
 
+-- | Get @ProjectRootUsability@ of a given file
+getProjectRootUsability :: FilePath -> IO ProjectRootUsability
+getProjectRootUsability filePath = do
+  exists <- doesFileExist filePath
+  if exists
+    then return ProjectRootUsabilityPresentAndUsable
+    else do
+      let isUsableAction =
+            handle @IOException
+              -- NOTE: if any IOException is raised, we assume the file does not exist.
+              -- That is what happen when we call @pathIsSymbolicLink@ on a @FilePath@ that does not exist.
+              (const $ pure False)
+              ((||) <$> pathIsSymbolicLink filePath <*> doesPathExist filePath)
+      isUnusable <- isUsableAction
+      if isUnusable
+        then return ProjectRootUsabilityPresentAndUnusable
+        else return ProjectRootUsabilityNotPresent
+
 -- | Find the root of this project.
 --
 -- The project directory will be one of the following:
@@ -552,27 +576,40 @@ findProjectRoot verbosity mprojectDir mprojectFile = do
             "Specifying an absolute path to the project file is deprecated."
               <> " Use --project-dir to set the project's directory."
 
-          doesFileExist file >>= \case
-            False -> left (BadProjectRootExplicitFile file)
-            True -> uncurry projectRoot =<< first dropTrailingPathSeparator . splitFileName <$> canonicalizePath file
+          getProjectRootUsability file >>= \case
+            ProjectRootUsabilityPresentAndUsable ->
+              uncurry projectRoot
+                =<< first dropTrailingPathSeparator . splitFileName <$> canonicalizePath file
+            ProjectRootUsabilityNotPresent ->
+              left (BadProjectRootExplicitFileNotFound file)
+            ProjectRootUsabilityPresentAndUnusable ->
+              left (BadProjectRootFileBroken file)
       | otherwise -> probeProjectRoot mprojectFile
     Just dir ->
       doesDirectoryExist dir >>= \case
-        False -> left (BadProjectRootDir dir)
+        False -> left (BadProjectRootDirNotFound dir)
         True -> do
           projectDir <- canonicalizePath dir
 
           case mprojectFile of
             Nothing -> pure $ Right (ProjectRootExplicit projectDir defaultProjectFile)
             Just projectFile
               | isAbsolute projectFile ->
-                  doesFileExist projectFile >>= \case
-                    False -> left (BadProjectRootAbsoluteFile projectFile)
-                    True -> Right . ProjectRootExplicitAbsolute dir <$> canonicalizePath projectFile
+                  getProjectRootUsability projectFile >>= \case
+                    ProjectRootUsabilityNotPresent ->
+                      left (BadProjectRootAbsoluteFileNotFound projectFile)
+                    ProjectRootUsabilityPresentAndUsable ->
+                      Right . ProjectRootExplicitAbsolute dir <$> canonicalizePath projectFile
+                    ProjectRootUsabilityPresentAndUnusable ->
+                      left (BadProjectRootFileBroken projectFile)
               | otherwise ->
-                  doesFileExist (projectDir </> projectFile) >>= \case
-                    False -> left (BadProjectRootDirFile dir projectFile)
-                    True -> projectRoot projectDir projectFile
+                  getProjectRootUsability (projectDir </> projectFile) >>= \case
+                    ProjectRootUsabilityNotPresent ->
+                      left (BadProjectRootDirFileNotFound dir projectFile)
+                    ProjectRootUsabilityPresentAndUsable ->
+                      projectRoot projectDir projectFile
+                    ProjectRootUsabilityPresentAndUnusable ->
+                      left (BadProjectRootFileBroken projectFile)
   where
     left = pure . Left
 
@@ -597,34 +634,50 @@ probeProjectRoot mprojectFile = do
         go dir | isDrive dir || dir == homedir =
           case mprojectFile of
             Nothing -> return (Right (ProjectRootImplicit startdir))
-            Just file -> return (Left (BadProjectRootExplicitFile file))
+            Just file -> return (Left (BadProjectRootExplicitFileNotFound file))
         go dir = do
-          exists <- doesFileExist (dir </> projectFileName)
-          if exists
-            then return (Right (ProjectRootExplicit dir projectFileName))
-            else go (takeDirectory dir)
+          getProjectRootUsability (dir </> projectFileName) >>= \case
+            ProjectRootUsabilityNotPresent ->
+              go (takeDirectory dir)
+            ProjectRootUsabilityPresentAndUsable ->
+              return (Right $ ProjectRootExplicit dir projectFileName)
+            ProjectRootUsabilityPresentAndUnusable ->
+              return (Left $ BadProjectRootFileBroken projectFileName)
 
 -- | Errors returned by 'findProjectRoot'.
 data BadProjectRoot
-  = BadProjectRootExplicitFile FilePath
-  | BadProjectRootDir FilePath
-  | BadProjectRootAbsoluteFile FilePath
-  | BadProjectRootDirFile FilePath FilePath
-  deriving (Show, Typeable)
+  = BadProjectRootExplicitFileNotFound FilePath
+  | BadProjectRootDirNotFound FilePath
+  | BadProjectRootAbsoluteFileNotFound FilePath
+  | BadProjectRootDirFileNotFound FilePath FilePath
+  | BadProjectRootFileBroken FilePath
+  deriving (Show, Typeable, Eq)
 
 instance Exception BadProjectRoot where
   displayException = renderBadProjectRoot
 
 renderBadProjectRoot :: BadProjectRoot -> String
 renderBadProjectRoot = \case
-  BadProjectRootExplicitFile projectFile ->
+  BadProjectRootExplicitFileNotFound projectFile ->
     "The given project file '" ++ projectFile ++ "' does not exist."
-  BadProjectRootDir dir ->
+  BadProjectRootDirNotFound dir ->
     "The given project directory '" <> dir <> "' does not exist."
-  BadProjectRootAbsoluteFile file ->
+  BadProjectRootAbsoluteFileNotFound file ->
     "The given project file '" <> file <> "' does not exist."
-  BadProjectRootDirFile dir file ->
+  BadProjectRootDirFileNotFound dir file ->
     "The given project directory/file combination '" <> dir </> file <> "' does not exist."
+  BadProjectRootFileBroken file ->
+    "The given project file '" <> file <> "' is broken. Is it a broken symbolic link?"
+
+-- | State of the project file, encodes if the file can be used
+data ProjectRootUsability
+  = -- | The file is present and can be used
+    ProjectRootUsabilityPresentAndUsable
+  | -- | The file is present but can't be used (e.g. broken symlink)
+    ProjectRootUsabilityPresentAndUnusable
+  | -- | The file is not present
+    ProjectRootUsabilityNotPresent
+  deriving (Eq, Show)
 
 withGlobalConfig
   :: Verbosity

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

@@ -98,6 +98,7 @@ tests =
       , testProperty "specific" prop_roundtrip_printparse_specific
       , testProperty "all" prop_roundtrip_printparse_all
       ]
+  , testGetProjectRootUsability
   , testFindProjectRoot
   ]
   where
@@ -106,6 +107,31 @@ tests =
         CompilerId GHC v -> v < mkVersion [7, 7]
         _ -> False
 
+testGetProjectRootUsability :: TestTree
+testGetProjectRootUsability =
+  testGroup
+    "getProjectRootUsability"
+    [ test "relative path" file ProjectRootUsabilityPresentAndUsable
+    , test "absolute path" absFile ProjectRootUsabilityPresentAndUsable
+    , test "symbolic link" fileSymlink ProjectRootUsabilityPresentAndUsable
+    , test "file not present" fileNotPresent ProjectRootUsabilityNotPresent
+    , test "directory" brokenDirCabalProject ProjectRootUsabilityPresentAndUnusable
+    , test "broken symbolic link" fileSymlinkBroken ProjectRootUsabilityPresentAndUnusable
+    ]
+  where
+    dir = fixturesDir </> "project-root"
+    file = defaultProjectFile
+    absFile = dir </> file
+    fileNotPresent = file <.> "not-present"
+    fileSymlink = file <.> "symlink"
+    fileSymlinkBroken = fileSymlink <.> "broken"
+    brokenDirCabalProject = "cabal" <.> "project" <.> "dir" <.> "broken"
+    test name fileName expectedState =
+      testCase name $
+        withCurrentDirectory dir $
+          getProjectRootUsability fileName
+            >>= (@?= expectedState)
+
 testFindProjectRoot :: TestTree
 testFindProjectRoot =
   testGroup
@@ -116,6 +142,10 @@ testFindProjectRoot =
     , test "explicit file in lib" (cd libDir) Nothing (Just file) (succeeds dir file)
     , test "other file" (cd dir) Nothing (Just fileOther) (succeeds dir fileOther)
     , test "other file in lib" (cd libDir) Nothing (Just fileOther) (succeeds dir fileOther)
+    , test "symbolic link" (cd dir) Nothing (Just fileSymlink) (succeeds dir fileSymlink)
+    , test "symbolic link in lib" (cd libDir) Nothing (Just fileSymlink) (succeeds dir fileSymlink)
+    , test "broken symbolic link" (cd dir) Nothing (Just fileSymlinkBroken) (failsWith $ BadProjectRootFileBroken fileSymlinkBroken)
+    , test "broken symbolic link in lib" (cd libDir) Nothing (Just fileSymlinkBroken) (failsWith $ BadProjectRootFileBroken fileSymlinkBroken)
     , -- Deprecated use-case
       test "absolute file" Nothing Nothing (Just absFile) (succeeds dir file)
     , test "nested file" (cd dir) Nothing (Just nixFile) (succeeds dir nixFile)
@@ -137,6 +167,9 @@ testFindProjectRoot =
     nixFile = "nix" </> file
     nixOther = nixFile <.> "other"
 
+    fileSymlink = file <.> "symlink"
+    fileSymlinkBroken = fileSymlink <.> "broken"
+
     missing path = Just (path <.> "does_not_exist")
 
     test name wrap projectDir projectFile validate =
@@ -165,6 +198,18 @@ testFindProjectRoot =
       Left _ -> pure ()
       Right x -> assertFailure $ "Expected an error, but found " <> show x
 
+    failsWith expectedError result = case result of
+      Left actualError ->
+        if actualError == expectedError
+          then pure ()
+          else
+            assertFailure $
+              "Expected an error "
+                <> show expectedError
+                <> ", but found "
+                <> show actualError
+      Right x -> assertFailure $ "Expected an error, but found " <> show x
+
 fixturesDir :: FilePath
 fixturesDir =
   unsafePerformIO $

cabal-install/tests/fixtures/project-root/cabal.project.symlink

@@ -0,0 +1 @@
+cabal.project

cabal-install/tests/fixtures/project-root/cabal.project.symlink.broken

@@ -0,0 +1 @@
+does-not-exist

changelog.d/pr-10103

@@ -0,0 +1,14 @@
+synopsis: Enhance error detection for cabal root project files, including broken symlinks
+
+packages: cabal-install
+
+prs: #10103
+
+issues: #9937
+
+description: {
+
+- Added proper detection and reporting for issues with cabal root project files. Previously, these files were silently ignored if they were broken symlinks. Now, `cabal` will exit 
+with an error in such case.
+
+}