lib:Cabal - do not use GHC to configure LD.

Cabal uses a peculiar c program to check if LD supports and should
use -x. To do this, it shells out to GHC to compiler the C file.
This however requires that GHC will not bail out, yet cabal does
not pass --package-db flags to this GHC invocation, and as such we
can run into situations where GHC bails out, especially during GHC
bootstrap phases where not all boot packages are available.

We however do not need GHC to compiler a c program, and can rely
on the C compiler.

Fundamentally cabal does not allow modelling program dependencies
in the program db, as such we must configure gcc first before using
it.

We make a small change to lib:Cabal (specifically the GHC module,
and it's Internal companion) to allow it to configure gcc first,
before trying to configure ld, and thus having gcc in scope while
configuring ld. This removes the need for the awkward ghc
invocation to compiler the test program.

Author: angerman

Cabal/src/Distribution/Simple/GHC.hs

@@ -263,8 +263,10 @@ configure verbosity hcPath hcPkgPath conf0 = do
           , compilerProperties = ghcInfoMap
           }
       compPlatform = Internal.targetPlatform ghcInfo
-      -- configure gcc and ld
-      progdb4 = Internal.configureToolchain implInfo ghcProg ghcInfoMap progdb3
+  -- configure gcc and ld
+  -- similarly to how we need ghc above, we need to know the c compiler
+  -- generally named `gcc` in cabal, to configure other programs, e.g. ld.
+  progdb4 <- Internal.configureToolchain verbosity implInfo ghcProg ghcInfoMap progdb3
   return (comp, compPlatform, progdb4)
 
 -- | Given something like /usr/local/bin/ghc-6.6.1(.exe) we try and find

Cabal/src/Distribution/Simple/GHC/Internal.hs

@@ -103,32 +103,42 @@ targetPlatform ghcInfo = platformFromTriple =<< lookup "Target platform" ghcInfo
 
 -- | Adjust the way we find and configure gcc and ld
 configureToolchain
-  :: GhcImplInfo
+  :: Verbosity
+  -> GhcImplInfo
   -> ConfiguredProgram
   -> Map String String
   -> ProgramDb
-  -> ProgramDb
-configureToolchain _implInfo ghcProg ghcInfo =
-  addKnownProgram
-    gccProgram
-      { programFindLocation = findProg gccProgramName extraGccPath
-      , programPostConf = configureGcc
-      }
-    . addKnownProgram
-      ldProgram
-        { programFindLocation = findProg ldProgramName extraLdPath
-        , programPostConf = \v cp ->
-            -- Call any existing configuration first and then add any new configuration
-            configureLd v =<< programPostConf ldProgram v cp
-        }
-    . addKnownProgram
-      arProgram
-        { programFindLocation = findProg arProgramName extraArPath
-        }
-    . addKnownProgram
-      stripProgram
-        { programFindLocation = findProg stripProgramName extraStripPath
-        }
+  -> IO ProgramDb
+configureToolchain verbosity _implInfo ghcProg ghcInfo db = do
+    -- this is a bit of a hack. We have a dependency of ld on gcc.
+    -- ld needs to compiler a c program, to check an ld feature.
+    -- we _could_ use ghc as a c frontend, but we do not pass all
+    -- db stack appropriately, and thus we can run into situations
+    -- where GHC will fail if it's stricter in it's wired-in-unit
+    -- selction and has the wrong db stack. However we don't need
+    -- ghc to compile a _test_ c program. So we configure `gcc`
+    -- first and then use `gcc` (the generic c compiler in cabal
+    -- terminology) to compile the test program.
+    let db' = flip addKnownProgram db $
+                gccProgram
+                  { programFindLocation = findProg gccProgramName extraGccPath
+                  , programPostConf = configureGcc
+                  }
+    (gccProg, db'') <- requireProgram verbosity gccProgram db'
+    return $ flip addKnownPrograms db'' $
+      [ ldProgram
+          { programFindLocation = findProg ldProgramName extraLdPath
+          , programPostConf = \v cp ->
+              -- Call any existing configuration first and then add any new configuration
+              configureLd gccProg v =<< programPostConf ldProgram v cp
+          }
+      , arProgram
+          { programFindLocation = findProg arProgramName extraArPath
+          }
+      , stripProgram
+          { programFindLocation = findProg stripProgramName extraStripPath
+          }
+      ]
   where
     compilerDir, base_dir, mingwBinDir :: FilePath
     compilerDir = takeDirectory (programPath ghcProg)
@@ -214,27 +224,26 @@ configureToolchain _implInfo ghcProg ghcInfo =
                 ++ gccLinkerFlags
           }
 
-    configureLd :: Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
-    configureLd v ldProg = do
-      ldProg' <- configureLd' v ldProg
+    configureLd :: ConfiguredProgram -> Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
+    configureLd gccProg v ldProg = do
+      ldProg' <- configureLd' gccProg v ldProg
       return
         ldProg'
           { programDefaultArgs = programDefaultArgs ldProg' ++ ldLinkerFlags
           }
 
     -- we need to find out if ld supports the -x flag
-    configureLd' :: Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
-    configureLd' verbosity ldProg = do
+    configureLd' :: ConfiguredProgram -> Verbosity -> ConfiguredProgram -> IO ConfiguredProgram
+    configureLd' gccProg verbosity ldProg = do
       ldx <- withTempFile ".c" $ \testcfile testchnd ->
         withTempFile ".o" $ \testofile testohnd -> do
           hPutStrLn testchnd "int foo() { return 0; }"
           hClose testchnd
           hClose testohnd
           runProgram
             verbosity
-            ghcProg
-            [ "-hide-all-packages"
-            , "-c"
+            gccProg
+            [ "-c"
             , testcfile
             , "-o"
             , testofile