Implement --cabal-file, allows multiple Cabal files in directory

Cabal/Distribution/PackageDescription/Check.hs

@@ -1563,7 +1563,13 @@ checkCabalFileBOM :: Monad m => CheckPackageContentOps m
 checkCabalFileBOM ops = do
   epdfile <- findPackageDesc ops
   case epdfile of
-    Left pc      -> return $ Just pc
+    -- MASSIVE HACK.  If the Cabal file doesn't exist, that is
+    -- a very strange situation to be in, because the driver code
+    -- in 'Distribution.Setup' ought to have noticed already!
+    -- But this can be an issue, see #3552 and also when
+    -- --cabal-file is specified.  So if you can't find the file,
+    -- just don't bother with this check.
+    Left _       -> return $ Nothing
     Right pdfile -> (flip check pc . startsWithBOM . fromUTF8)
                     `liftM` (getFileContents ops pdfile)
       where pc = PackageDistInexcusable $
@@ -1597,7 +1603,7 @@ findPackageDesc ops
              ++ "Please create a package description file <pkgname>.cabal"
 
     multiDesc :: [String] -> String
-    multiDesc l = "Multiple cabal files found.\n"
+    multiDesc l = "Multiple cabal files found while checking.\n"
                   ++ "Please use only one of: "
                   ++ intercalate ", " l
 

Cabal/Distribution/Simple.hs

@@ -192,6 +192,7 @@ configureAction hooks flags args = do
     pbi <- preConf hooks args flags'
 
     (mb_pd_file, pkg_descr0) <- confPkgDescr hooks verbosity
+                                    (flagToMaybe (configCabalFilePath flags))
 
     let epkg_descr = (pkg_descr0, pbi)
 
@@ -211,13 +212,15 @@ configureAction hooks flags args = do
   where
     verbosity = fromFlag (configVerbosity flags)
 
-confPkgDescr :: UserHooks -> Verbosity -> IO (Maybe FilePath, GenericPackageDescription)
-confPkgDescr hooks verbosity = do
+confPkgDescr :: UserHooks -> Verbosity -> Maybe FilePath -> IO (Maybe FilePath, GenericPackageDescription)
+confPkgDescr hooks verbosity mb_path = do
   mdescr <- readDesc hooks
   case mdescr of
     Just descr -> return (Nothing, descr)
     Nothing -> do
-        pdfile <- defaultPackageDesc verbosity
+        pdfile <- case mb_path of
+                    Nothing -> defaultPackageDesc verbosity
+                    Just path -> return path
         descr  <- readPackageDescription verbosity pdfile
         return (Just pdfile, descr)
 
@@ -293,7 +296,7 @@ cleanAction hooks flags args = do
 
     pbi <- preClean hooks args flags'
 
-    (_, ppd) <- confPkgDescr hooks verbosity
+    (_, ppd) <- confPkgDescr hooks verbosity Nothing
     -- It might seem like we are doing something clever here
     -- but we're really not: if you look at the implementation
     -- of 'clean' in the end all the package description is
@@ -337,7 +340,18 @@ sdistAction hooks flags args = do
 
     mlbi <- maybeGetPersistBuildConfig distPref
 
-    (_, ppd) <- confPkgDescr hooks verbosity
+    -- NB: It would be TOTALLY WRONG to use the 'PackageDescription'
+    -- store in the 'LocalBuildInfo' for the rest of @sdist@, because
+    -- that would result in only the files that would be built
+    -- according to the user's configure being packaged up.
+    -- In fact, it is not obvious why we need to read the
+    -- 'LocalBuildInfo' in the first place, except that we want
+    -- to do some architecture-independent preprocessing which
+    -- needs to be configured.  This is totally awful, see
+    -- GH#130.
+
+    (_, ppd) <- confPkgDescr hooks verbosity Nothing
+
     let pkg_descr0 = flattenPackageDescription ppd
     sanityCheckHookedBuildInfo pkg_descr0 pbi
     let pkg_descr = updatePackageDescription pbi pkg_descr0

Cabal/Distribution/Simple/Setup.hs

@@ -393,6 +393,7 @@ data ConfigFlags = ConfigFlags {
     configIPID          :: Flag String, -- ^ explicit IPID to be used
 
     configDistPref :: Flag FilePath, -- ^"dist" prefix
+    configCabalFilePath :: Flag FilePath, -- ^ Cabal file to use
     configVerbosity :: Flag Verbosity, -- ^verbosity level
     configUserInstall :: Flag Bool,    -- ^The --user\/--global flag
     configPackageDBs :: [Maybe PackageDB], -- ^Which package DBs to use
@@ -452,6 +453,7 @@ defaultConfigFlags progConf = emptyConfigFlags {
     configProgPrefix   = Flag (toPathTemplate ""),
     configProgSuffix   = Flag (toPathTemplate ""),
     configDistPref     = NoFlag,
+    configCabalFilePath = NoFlag,
     configVerbosity    = Flag normal,
     configUserInstall  = Flag False,           --TODO: reverse this
 #if defined(mingw32_HOST_OS)
@@ -518,6 +520,11 @@ configureOptions showOrParseArgs =
                     , (Flag (HaskellSuite "haskell-suite"), ([] , ["haskell-suite"]),
                         "compile with a haskell-suite compiler")])
 
+      ,option "" ["cabal-file"]
+         "use this Cabal file"
+         configCabalFilePath (\v flags -> flags { configCabalFilePath = v })
+         (reqArgFlag "PATH")
+
       ,option "w" ["with-compiler"]
          "give the path to a particular compiler"
          configHcPath (\v flags -> flags { configHcPath = v })

cabal-install/Distribution/Client/Config.hs

@@ -302,6 +302,7 @@ instance Semigroup SavedConfig where
         configExtraIncludeDirs    = lastNonEmpty configExtraIncludeDirs,
         configIPID                = combine configIPID,
         configDistPref            = combine configDistPref,
+        configCabalFilePath       = combine configCabalFilePath,
         configVerbosity           = combine configVerbosity,
         configUserInstall         = combine configUserInstall,
         -- TODO: NubListify

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

@@ -554,6 +554,7 @@ convertToLegacyAllPackageConfig
       configInstallDirs         = mempty,
       configScratchDir          = mempty,
       configDistPref            = mempty,
+      configCabalFilePath       = mempty,
       configVerbosity           = mempty,
       configUserInstall         = mempty, --projectConfigUserInstall,
       configPackageDBs          = mempty, --projectConfigPackageDBs,
@@ -616,6 +617,7 @@ convertToLegacyPerPackageConfig PackageConfig {..} =
       configInstallDirs         = mempty,
       configScratchDir          = mempty,
       configDistPref            = mempty,
+      configCabalFilePath       = mempty,
       configVerbosity           = mempty,
       configUserInstall         = mempty,
       configPackageDBs          = mempty,

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -1947,6 +1947,7 @@ setupHsConfigureFlags (ReadyPackage
         (Cabal.ConfigFlags {..})
   where
     configDistPref            = toFlag builddir
+    configCabalFilePath       = mempty
     configVerbosity           = toFlag verbosity
 
     configIPID                = toFlag (display (installedUnitId pkg))