More descriptive errors when .cabal file is missing

Particularly when dealing with add-source dependencies, it is useful to know
in which directory cabal can't find a .cabal file, see:
#1816

Errors are also improved when installing local packages, e.g. `cabal install
another/directory`.

Author: owst

cabal-install/Distribution/Client/IndexUtils.hs

@@ -55,7 +55,7 @@ import Distribution.Text
 import Distribution.Verbosity
          ( Verbosity, normal, lessVerbose )
 import Distribution.Simple.Utils
-         ( die, warn, info, fromUTF8, tryFindPackageDesc )
+         ( die, warn, info, fromUTF8 )
 
 import Data.Char   (isAlphaNum)
 import Data.Maybe  (mapMaybe, fromMaybe)
@@ -69,7 +69,8 @@ import qualified Data.ByteString.Lazy.Char8 as BS.Char8
 import qualified Data.ByteString.Char8 as BSS
 import Data.ByteString.Lazy (ByteString)
 import Distribution.Client.GZipUtils (maybeDecompress)
-import Distribution.Client.Utils (byteStringToFilePath)
+import Distribution.Client.Utils ( byteStringToFilePath
+                                 , tryFindAddSourcePackageDesc )
 import Distribution.Compat.Exception (catchIO)
 import Distribution.Client.Compat.Time (getFileAge, getModTime)
 import System.Directory (doesFileExist)
@@ -351,7 +352,8 @@ extractPkg entry blockNo = case Tar.entryContent entry of
     | Tar.isBuildTreeRefTypeCode typeCode ->
       Just $ do
         let path   = byteStringToFilePath content
-        cabalFile <- tryFindPackageDesc path
+            err = "Error reading package index."
+        cabalFile <- tryFindAddSourcePackageDesc path err
         descr     <- PackageDesc.Parse.readPackageDescription normal cabalFile
         return $ BuildTreeRef (refTypeFromTypeCode typeCode) (packageId descr)
                               descr path blockNo
@@ -452,8 +454,9 @@ packageIndexFromCache mkPkg hnd entrs mode = accum mempty [] entrs
       -- package id for build tree references - the user might edit the .cabal
       -- file after the reference was added to the index.
       path <- liftM byteStringToFilePath . getEntryContent $ blockno
-      pkg  <- do cabalFile <- tryFindPackageDesc path
-                 PackageDesc.Parse.readPackageDescription normal cabalFile
+      pkg  <- do let err = "Error reading package index from cache."
+                 file <- tryFindAddSourcePackageDesc path err
+                 PackageDesc.Parse.readPackageDescription normal file
       let srcpkg = mkPkg (BuildTreeRef refType (packageId pkg) pkg path blockno)
       accum (srcpkg:srcpkgs) prefs entries
 

cabal-install/Distribution/Client/Sandbox.hs

@@ -64,7 +64,8 @@ import Distribution.Client.Sandbox.Types      ( SandboxPackageInfo(..)
                                               , UseSandbox(..) )
 import Distribution.Client.Types              ( PackageLocation(..)
                                               , SourcePackage(..) )
-import Distribution.Client.Utils              ( inDir, tryCanonicalizePath )
+import Distribution.Client.Utils              ( inDir, tryCanonicalizePath
+                                              , tryFindAddSourcePackageDesc )
 import Distribution.PackageDescription.Configuration
                                               ( flattenPackageDescription )
 import Distribution.PackageDescription.Parse  ( readPackageDescription )
@@ -80,7 +81,6 @@ import Distribution.Simple.Setup              ( Flag(..), HaddockFlags(..)
 import Distribution.Simple.SrcDist            ( prepareTree )
 import Distribution.Simple.Utils              ( die, debug, notice, info, warn
                                               , debugNoWrap, defaultPackageDesc
-                                              , tryFindPackageDesc
                                               , intercalate, topHandlerWith
                                               , createDirectoryIfMissingVerbose )
 import Distribution.Package                   ( Package(..) )
@@ -618,9 +618,9 @@ withSandboxPackageInfo verbosity configFlags globalFlags
   -- List all packages installed in the sandbox.
   installedPkgIndex <- getInstalledPackagesInSandbox verbosity
                        configFlags comp conf
-
+  let err = "Error reading sandbox package information."
   -- Get the package descriptions for all add-source deps.
-  depsCabalFiles <- mapM tryFindPackageDesc buildTreeRefs
+  depsCabalFiles <- mapM (flip tryFindAddSourcePackageDesc err) buildTreeRefs
   depsPkgDescs   <- mapM (readPackageDescription verbosity) depsCabalFiles
   let depsMap           = M.fromList (zip buildTreeRefs depsPkgDescs)
       isInstalled pkgid = not . null

cabal-install/Distribution/Client/Sandbox/Index.hs

@@ -29,9 +29,10 @@ import Distribution.Client.Types ( Repo(..), LocalRepo(..)
                                  , SourcePackage(..), PackageLocation(..) )
 import Distribution.Client.Utils ( byteStringToFilePath, filePathToByteString
                                  , makeAbsoluteToCwd, tryCanonicalizePath
-                                 , canonicalizePathNoThrow )
+                                 , canonicalizePathNoThrow
+                                 , tryFindAddSourcePackageDesc  )
 
-import Distribution.Simple.Utils ( die, debug, tryFindPackageDesc )
+import Distribution.Simple.Utils ( die, debug )
 import Distribution.Verbosity    ( Verbosity )
 
 import qualified Data.ByteString.Lazy as BS
@@ -61,7 +62,7 @@ buildTreeRefFromPath refType dir = do
   dirExists <- doesDirectoryExist dir
   unless dirExists $
     die $ "directory '" ++ dir ++ "' does not exist"
-  _ <- tryFindPackageDesc dir
+  _ <- tryFindAddSourcePackageDesc dir "Error adding source reference."
   return . Just $ BuildTreeRef refType dir
 
 -- | Given a tar archive entry, try to parse it as a local build tree reference.

cabal-install/Distribution/Client/Sandbox/Timestamp.hs

@@ -31,8 +31,7 @@ import Distribution.Simple.Setup                     (Flag (..),
                                                       SDistFlags (..),
                                                       defaultSDistFlags,
                                                       sdistCommand)
-import Distribution.Simple.Utils                     (debug, die,
-                                                      tryFindPackageDesc, warn)
+import Distribution.Simple.Utils                     (debug, die, warn)
 import Distribution.System                           (Platform)
 import Distribution.Text                             (display)
 import Distribution.Verbosity                        (Verbosity, lessVerbose,
@@ -47,7 +46,8 @@ import Distribution.Client.SetupWrapper              (SetupScriptOptions (..),
                                                       defaultSetupScriptOptions,
                                                       setupWrapper)
 import Distribution.Client.Utils                     (inDir, removeExistingFile,
-                                                      tryCanonicalizePath)
+                                                      tryCanonicalizePath,
+                                                      tryFindAddSourcePackageDesc)
 
 import Distribution.Compat.Exception                 (catchIO)
 import Distribution.Client.Compat.Time               (EpochTime, getCurTime,
@@ -213,9 +213,10 @@ withActionOnCompilerTimestamps f sandboxDir compId platform act = do
 -- FIXME: This function is not thread-safe because of 'inDir'.
 allPackageSourceFiles :: Verbosity -> FilePath -> IO [FilePath]
 allPackageSourceFiles verbosity packageDir = inDir (Just packageDir) $ do
-  pkg <- fmap (flattenPackageDescription)
-         . readPackageDescription verbosity =<< tryFindPackageDesc packageDir
-
+  pkg <- do
+    let err = "Error reading source files of add-source dependency."
+    desc <- tryFindAddSourcePackageDesc packageDir err
+    flattenPackageDescription `fmap` readPackageDescription verbosity desc
   let file      = "cabal-sdist-list-sources"
       flags     = defaultSDistFlags {
         sDistVerbosity   = Flag $ if verbosity == normal

cabal-install/Distribution/Client/Targets.hs

@@ -58,6 +58,7 @@ import Distribution.Client.PackageIndex (PackageIndex)
 import qualified Distribution.Client.PackageIndex as PackageIndex
 import qualified Distribution.Client.Tar as Tar
 import Distribution.Client.FetchUtils
+import Distribution.Client.Utils ( tryFindPackageDesc )
 
 import Distribution.PackageDescription
          ( GenericPackageDescription, FlagName(..), FlagAssignment )
@@ -70,7 +71,7 @@ import Distribution.Text
          ( Text(..), display )
 import Distribution.Verbosity (Verbosity)
 import Distribution.Simple.Utils
-         ( die, warn, intercalate, tryFindPackageDesc, fromUTF8, lowercase )
+         ( die, warn, intercalate, fromUTF8, lowercase )
 
 import Data.List
          ( find, nub )
@@ -422,7 +423,7 @@ expandUserTarget worldFile userTarget = case userTarget of
 
     UserTargetLocalCabalFile file -> do
       let dir = takeDirectory file
-      _   <- tryFindPackageDesc dir -- just as a check
+      _   <- tryFindPackageDesc dir (localPackageError dir) -- just as a check
       return [ PackageTargetLocation (LocalUnpackedPackage dir) ]
 
     UserTargetLocalTarball tarballFile ->
@@ -431,6 +432,9 @@ expandUserTarget worldFile userTarget = case userTarget of
     UserTargetRemoteTarball tarballURL ->
       return [ PackageTargetLocation (RemoteTarballPackage tarballURL ()) ]
 
+localPackageError :: FilePath -> String
+localPackageError dir =
+    "Error reading local package.\nCouldn't find .cabal file in: " ++ dir
 
 -- ------------------------------------------------------------
 -- * Fetching and reading package targets
@@ -468,7 +472,8 @@ readPackageTarget verbosity target = case target of
     PackageTargetLocation location -> case location of
 
       LocalUnpackedPackage dir -> do
-        pkg <- readPackageDescription verbosity =<< tryFindPackageDesc dir
+        pkg <- tryFindPackageDesc dir (localPackageError dir) >>=
+                 readPackageDescription verbosity
         return $ PackageTargetLocation $
                    SourcePackage {
                      packageInfoId        = packageId pkg,

cabal-install/Distribution/Client/Utils.hs

@@ -8,12 +8,15 @@ module Distribution.Client.Utils ( MergeResult(..)
                                  , byteStringToFilePath, tryCanonicalizePath
                                  , canonicalizePathNoThrow
                                  , moreRecentFile, existsAndIsMoreRecentThan
+                                 , tryFindAddSourcePackageDesc
+                                 , tryFindPackageDesc
                                  , relaxEncodingErrors)
        where
 
 import Distribution.Compat.Exception   ( catchIO )
 import Distribution.Client.Compat.Time ( getModTime )
 import Distribution.Simple.Setup       ( Flag(..) )
+import Distribution.Simple.Utils       ( die, findPackageDesc )
 import qualified Data.ByteString.Lazy as BS
 import Control.Monad
          ( when )
@@ -216,3 +219,19 @@ relaxEncodingErrors handle = do
     _ ->
 #endif
       return ()
+
+-- |Like 'tryFindPackageDesc', but with error specific to add-source deps.
+tryFindAddSourcePackageDesc :: FilePath -> String -> IO FilePath
+tryFindAddSourcePackageDesc depPath err = tryFindPackageDesc depPath $
+    err ++ "\n" ++ "Failed to read cabal file of add-source dependency: "
+    ++ depPath
+
+-- |Try to find a @.cabal@ file, in directory @depPath@. Fails if one cannot be
+-- found, with @err@ prefixing the error message. This function simply allows
+-- us to give a more descriptive error than that provided by @findPackageDesc@.
+tryFindPackageDesc :: FilePath -> String -> IO FilePath
+tryFindPackageDesc depPath err = do
+    errOrCabalFile <- findPackageDesc depPath
+    case errOrCabalFile of
+        Right file -> return file
+        Left _ -> die err