fix(pkg): Check that git repo dir is accessible (#9019)

* fix(pkg): Check that git repo dir is accessible

Instead of going ahead and running git against something that is not an
accessible directory, this will at least raise an exception.

Are there better ways to solve it? Except for showing a possibly better
error message, not really - if someone has replaced the folder with
something we can't access there is no other option than to fail in some
way or other.

Signed-off-by: Marek Kubica <marek@tarides.com>

src/dune_pkg/rev_store.ml

@@ -48,13 +48,19 @@ let show { dir } (Rev rev) path =
 
 let load_or_create ~dir =
   let t = { dir } in
-  (* TODO might as well double check it's a directory *)
-  match Path.exists dir with
-  | true -> Fiber.return t
-  | false ->
-    Path.mkdir_p dir;
-    let+ () = run t [ "init"; "--bare" ] in
-    t
+  let* () = Fiber.return () in
+  let+ () =
+    match Fpath.mkdir_p (Path.to_string dir) with
+    | Already_exists -> Fiber.return ()
+    | Created -> run t [ "init"; "--bare" ]
+    | exception Unix.Unix_error (e, x, y) ->
+      User_error.raise
+        [ Pp.textf "%s isn't a directory" (Path.to_string_maybe_quoted dir)
+        ; Pp.textf "reason: %s" (Unix_error.Detailed.to_string_hum (e, x, y))
+        ]
+        ~hints:[ Pp.text "delete this file or check its permissions" ]
+  in
+  t
 ;;
 
 module Remote = struct