Fix OpamSystem.install for Windows

The install command doesn't make sense for Windows. OpamSystem.install
altered to use copying instead and also various checks added to guard
against package errors. In particular, .exe is automatically added to
executables (with a warning) if exec is true and warnings are displayed
if Cygwin-linked files or Unix shell-scripts are installed.

Signed-off-by: David Allsopp <david.allsopp@metastack.com>

src/core/opamSystem.ml

@@ -510,7 +510,13 @@ let read_command_output ?verbose ?env ?metadata ?allow_stdin cmd =
 let verbose_for_base_commands () =
   OpamCoreConfig.(!r.verbose_level) >= 3
 
-let copy_file src dst =
+let cygify f =
+  if Sys.win32 then
+    List.map (Lazy.force f)
+  else
+    fun x -> x
+
+let copy_file_aux f src dst =
   if (try Sys.is_directory src
       with Sys_error _ -> raise (File_not_found src))
   then internal_error "Cannot copy %s: it is a directory." src;
@@ -519,7 +525,9 @@ let copy_file src dst =
   if file_or_symlink_exists dst
   then remove_file dst;
   mkdir (Filename.dirname dst);
-  command ~verbose:(verbose_for_base_commands ()) ["cp"; src; dst ]
+  command ~verbose:(verbose_for_base_commands ()) ("cp"::(cygify f [src; dst]))
+
+let copy_file = copy_file_aux (get_cygpath_function ~command:"cp")
 
 let copy_dir src dst =
   if Sys.file_exists dst then
@@ -536,10 +544,12 @@ let copy_dir src dst =
      command ~verbose:(verbose_for_base_commands ())
        [ "cp"; "-PRp"; src; dst ])
 
-let mv src dst =
+let mv_aux f src dst =
   if file_or_symlink_exists dst then remove_file dst;
   mkdir (Filename.dirname dst);
-  command ~verbose:(verbose_for_base_commands ()) ["mv"; src; dst ]
+  command ~verbose:(verbose_for_base_commands ()) ("mv"::(cygify f [src; dst]))
+
+let mv = mv_aux (get_cygpath_function ~command:"mv")
 
 let is_exec file =
   let stat = Unix.stat file in
@@ -623,8 +633,42 @@ let install ?exec src dst =
   let exec = match exec with
     | Some e -> e
     | None -> is_exec src in
-  command ("install" :: "-m" :: (if exec then "0755" else "0644") ::
-     [ src; dst ])
+  begin
+    if Sys.win32 then
+      if exec then begin
+        let (dst, cygcheck) =
+          match classify_executable src with
+            `Exe _ ->
+              if not (Filename.check_suffix dst ".exe") && not (Filename.check_suffix dst ".dll") then begin
+                OpamConsole.warning "Automatically adding .exe to %s" dst;
+                (dst ^ ".exe", true)
+              end else
+                (dst, true)
+          | `Dll _ ->
+              (* TODO Installation of .dll to bin is unfortunate, but not sure if it should be a warning *)
+              (dst, true)
+          | `Script ->
+              (* TODO Generate a .cmd wrapper (and warn about it - they're not perfect) *)
+              OpamConsole.warning "%s is a script; the command won't be available" dst;
+              (dst, false)
+          | `Unknown ->
+              (* TODO Installation of a non-executable file is unexpected, but not sure if it should be a warning/error *)
+              (dst, false) in
+        copy_file src dst;
+        if cygcheck then
+          match OpamStd.Sys.is_cygwin_variant dst with
+            `Native ->
+              ()
+          | `Cygwin ->
+              OpamConsole.warning "%s is a Cygwin-linked executable" dst
+          | `CygLinked ->
+              OpamConsole.warning "%s links with a Cygwin-compiled DLL (almost certainly a packaging or environment error)" dst
+      end else
+        copy_file src dst
+    else
+      command ("install" :: "-m" :: (if exec then "0755" else "0644") ::
+         [ src; dst ])
+  end
 
 let cpu_count () =
   try