Merge pull request #4164 from abooij/issue-4156

First create then rename symlinks to fix #4156

Cabal/Distribution/Simple/GHC.hs

@@ -1521,10 +1521,18 @@ installFLib verbosity lbi targetDir builtDir _pkg flib =
 #ifndef mingw32_HOST_OS
           -- createSymbolicLink file1 file2 creates a symbolic link
           -- named file2 which points to the file file1.
-          -- Note that we do want a symlink to name rather than dst, because
-          -- the symlink will be relative to the directory it's created in.
-          createSymbolicLink name (dstDir </> flibBuildName lbi flib)
-          createSymbolicLink name (dstDir </> "lib" ++ nm <.> "so")
+          -- Note that we do want a symlink to 'name' rather than 'dst',
+          -- because the symlink will be relative to the directory it's created
+          -- in.
+          -- Finally, we first install in a temporary directory and then rename
+          -- to simulate a ln --force
+          withTempDirectory verbosity dstDir nm $ \tmpDir -> do
+              let link1 = flibBuildName lbi flib
+                  link2 = "lib" ++ nm <.> "so"
+              createSymbolicLink name (tmpDir </> link1)
+              renameFile (tmpDir </> link1) (dstDir </> link1)
+              createSymbolicLink name (tmpDir </> link2)
+              renameFile (tmpDir </> link2) (dstDir </> link2)
         where
           nm :: String
           nm = unUnqualComponentName $ foreignLibName flib

cabal-testsuite/PackageTests/ForeignLibs/setup.test.hs

@@ -26,6 +26,7 @@ main = setupAndCabalTest $ do
     skipUnless =<< ghcVersionIs (>= mkVersion [7,8])
     withPackageDb $ do
         setup_install []
+        setup "copy" [] -- regression test #4156
         dist_dir <- fmap testDistDir getTestEnv
         lbi <- getLocalBuildInfoM
         let installDirs = absoluteInstallDirs (localPkgDescr lbi) lbi NoCopyDest