Fix remaining getDirectoryFiles[IO] call-sites.

This fix addresses the fact that paths returned by `getDirectoryFiles`
and `getDirectoryFilesIO` are always relative to their first argument;
an empty directory defaulting to the "current directory".

To avoid any ambiguity, this change ensures that the first argument in
any call to those functions is either set to `top` -- if the files are
expected to be in the source tree -- or `root` -- if they are expected
to be in the build artifact tree.

hadrian/src/Rules/Gmp.hs

@@ -17,8 +17,8 @@ gmpObjects = do
     -- The line below causes a Shake Lint failure on Windows, which forced us to
     -- disable Lint by default. See more details here:
     -- https://ghc.haskell.org/trac/ghc/ticket/15971.
-    map unifyPath <$>
-        liftIO (getDirectoryFilesIO "" [gmpPath -/- gmpObjectsDir -/- "*.o"])
+    map (unifyPath . (gmpPath -/-)) <$>
+        liftIO (getDirectoryFilesIO gmpPath [gmpObjectsDir -/- "*.o"])
 
 gmpBase :: FilePath
 gmpBase = pkgPath integerGmp -/- "gmp"
@@ -108,18 +108,19 @@ gmpRules = do
     -- Extract in-tree GMP sources and apply patches
     root <//> "gmp/Makefile.in" %> \_ -> do
         gmpPath <- gmpBuildPath
+        top <- topDirectory
         removeDirectory gmpPath
         -- Note: We use a tarball like gmp-4.2.4-nodoc.tar.bz2, which is
         -- gmp-4.2.4.tar.bz2 repacked without the doc/ directory contents.
         -- That's because the doc/ directory contents are under the GFDL,
         -- which causes problems for Debian.
         tarball <- unifyPath . fromSingleton "Exactly one GMP tarball is expected"
-               <$> getDirectoryFiles "" [gmpBase -/- "gmp-tarballs/gmp*.tar.bz2"]
+               <$> getDirectoryFiles top [gmpBase -/- "gmp-tarballs/gmp*.tar.bz2"]
 
         withTempDir $ \dir -> do
             let tmp = unifyPath dir
-            need [tarball]
-            build $ target gmpContext (Tar Extract) [tarball] [tmp]
+            need [top -/- tarball]
+            build $ target gmpContext (Tar Extract) [top -/- tarball] [tmp]
 
             let patch     = gmpBase -/- "gmpsrc.patch"
                 patchName = takeFileName patch

hadrian/src/Rules/Libffi.hs

@@ -81,10 +81,11 @@ libffiRules =
       root -/- stageString stage -/- "libffi/build/Makefile.in" %> \mkIn -> do
         libffiPath <- libffiBuildPath stage
         removeDirectory libffiPath
+        top <- topDirectory
         tarball <- unifyPath . fromSingleton "Exactly one LibFFI tarball is expected"
-               <$> getDirectoryFiles "" ["libffi-tarballs/libffi*.tar.gz"]
+               <$> getDirectoryFiles top ["libffi-tarballs/libffi*.tar.gz"]
 
-        need [tarball]
+        need [top -/- tarball]
         -- Go from 'libffi-3.99999+git20171002+77e130c.tar.gz' to 'libffi-3.99999'
         let libname = takeWhile (/= '+') $ takeFileName tarball
 
@@ -93,12 +94,11 @@ libffiRules =
         -- TODO: Simplify.
         actionFinally (do
           build $ target (libffiContext stage) (Tar Extract)
-                                                  [tarball]
+                                                  [top -/- tarball]
                                                   [root -/- stageString stage]
           moveDirectory (root -/- stageString stage -/- libname) libffiPath)  $
             removeFiles (root -/- stageString stage) [libname <//> "*"]
 
-        top <- topDirectory
         fixFile mkIn (fixLibffiMakefile top)
 
       -- TODO: Get rid of hard-coded @libffi@.