Allow a GhcInstallAction to skip directory enumeration

The Windows build is different from the other builds in a few
ways, one of which is very important for this commit:

* Windows installs HP and GHC in a single directory, so
  creating dependencies too early on the contents of the
  target GHC directory contents will cause Shake to complain
  that the directory contents have changed since making a
  dependency on them (which they have, since later, the
  HP-built packages need to come into that set of
  directories).  So, after building the ghcVirtualTarget, we
  do not want the directory contents accounted for as
  dependencies just yet (it is done later for the entire
  target directory).

In the osGhcTargetInstall function in the Windows builds, the
directory is not completed at the point this action is used,
so we cannot have the Shake system enumerating this directory
for dependencies too soon.  So we must make its
osGhcTargetInstall no longer returns a directory, which
prevents the vTarget code in Dirs.hs from making dependencies
of the directory contents too soon.

This change is part of a larger change but it is separated
here as this isolates any effects on the common code.  The
Windows-specific changes will be in a separate commit for
bookkeeping reasons.  The GhcInstallAction type is only used
internally to GhcDist and for the Windows case where it is
the only build (currently) to use the GhcInstallCustom
variant of the GhcInstall type.

* hptool/src/OS/Win.hs
  * With this change to GhcInstallAction, the
    osGhcTargetInstall function can now elide the
    (incomplete) FilePath.
* hptool/src/Types.hs
  * Allow the FilePath returned by a GhcInstallAction, to be
    optional.
* hptool/src/OS/Win/WinRules.hs
  * Track GhcInstallAction change
* hptool/src/GhcDist.hs
  * Allow the handling of ghcVirtualTarget to accomodate the
    case of not providing a FilePath, which will prevent the
    vdir code from creating dependencies on the contents.

Author: randen

hptool/src/GhcDist.hs

@@ -39,7 +39,7 @@ cppCommandFlags cpp = case cpp of
 
 
 ghcInstall :: GhcInstall ->
-              FilePath -> Maybe (BuildConfig -> FilePath) -> Action FilePath
+              FilePath -> Maybe (BuildConfig -> FilePath) -> Action (Maybe FilePath)
 ghcInstall postUntarAction base mfPrefix = do
     tarFile <- askGhcBinDistTarFile
     conf <- askBuildConfig
@@ -74,7 +74,7 @@ ghcInstallConfigure base mfPrefix conf distDir = do
     Just cppCommand <- getCppCommand settings settingsFile
     writeSettings settingsFile (updateCppFlags cppCommand settings)
 
-    return destDir
+    return . Just $ destDir
   where
     layout Nothing = (base, base)
     layout (Just p) = (p, base </+> p)
@@ -113,7 +113,7 @@ ghcDistRules = do
         ghcInstall postUntar ghcLocalDir Nothing >> return ()
     ghcVirtualTarget ~/> do
         postUntar <- osGhcTargetInstall . osFromConfig <$> askBuildConfig
-        ghcInstall postUntar targetDir (Just targetPrefix) >>= return . Just
+        ghcInstall postUntar targetDir (Just targetPrefix)
   where
     targetPrefix = osGhcPrefix . osFromConfig
 

hptool/src/OS/Win.hs

@@ -54,10 +54,12 @@ winOsFromConfig BuildConfig{..} = os
         -- dependencies on the contents of winGhcTargetDir won't account
         -- for the HP pieces.  Also, for Windows, the ghc-bindist/local and
         -- the GHC installed into the targetDir should be identical.
-        -- osTargetAction is the right place to do the targetDir snapshot.
+        -- It is incorrect to return anything here since the
+        -- dir which we just processed is not completed yet (as mentioned
+        -- above, we need to await the hp-specific packages to be built).
         GhcInstallCustom $ \bc distDir -> do
             void $ winGhcInstall winGhcTargetDir bc distDir
-            return ghcLocalDir
+            return Nothing
 
     osPackageTargetDir p = winHpPrefix </> packagePattern p
 

hptool/src/OS/Win/WinRules.hs

@@ -56,7 +56,7 @@ winGhcInstall destDir bc distDir = do
         winGlutIncSrcs
     needContents winGlutIncludeInstallDir
 
-    return destDir
+    return . Just $ destDir
 
 
 copyWinTargetExtras :: BuildConfig -> Action ()

hptool/src/Types.hs

@@ -116,7 +116,7 @@ data BuildConfig = BuildConfig
 -- | A function that is used for the actions after untar-ing GHC.
 -- The build configuration and file path of the untar-ed directory is
 -- provided, and the file path of the installed directory is returned.
-type GhcInstallAction = BuildConfig -> FilePath -> Action FilePath
+type GhcInstallAction = BuildConfig -> FilePath -> Action (Maybe FilePath)
 
 -- | After untar-ing GHC, some platforms require configure-make, while
 -- other platforms need other custom steps.