Windows: Handle shebang in external special remote program.

Utility/Shell.hs

@@ -9,6 +9,19 @@
 
 module Utility.Shell where
 
+import Utility.SafeCommand
+#ifdef mingw32_HOST_OS
+import Utility.Path
+import Utility.FileSystemEncoding
+import Utility.Exception
+import Utility.PartialPrelude
+#endif
+
+#ifdef mingw32_HOST_OS
+import System.IO
+import System.FilePath
+#endif
+
 shellPath_portable :: FilePath
 shellPath_portable = "/bin/sh"
 
@@ -24,3 +37,32 @@ shebang_portable = "#!" ++ shellPath_portable
 
 shebang_local :: String
 shebang_local = "#!" ++ shellPath_local
+
+-- | On Windows, shebang is not handled by the kernel, so to support
+-- shell scripts etc, have to look at the program being run and
+-- parse it for shebang.
+--
+-- This has no effect on Unix.
+findShellCommand :: FilePath -> IO (FilePath, [CommandParam])
+findShellCommand f = do
+#ifndef mingw32_HOST_OS
+	defcmd
+#else
+	l <- catchDefaultIO Nothing $ withFile f ReadMode $ \h -> do
+		fileEncoding h
+		headMaybe . lines <$> hGetContents h
+	case l of
+		Just ('#':'!':rest) -> case words rest of
+			[] -> defcmd
+			(c:ps) -> do
+				let ps' = map Param ps ++ [File f]
+				-- If the command is not inPath,
+				-- take the base of it, and run eg "sh"
+				-- which in some cases on windows will work
+				-- despite it not being inPath.
+				ok <- inPath c
+				return (if ok then c else takeFileName c, ps')
+		_ -> defcmd
+#endif
+  where
+	defcmd = return (f, [])