refactor: extract [Fpath.mkdir_p_strict] (#13515)

This function will be useful elsewhere

---------

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

Author: rgrinberg

bin/install_uninstall.ml

@@ -357,17 +357,11 @@ module File_ops_real (W : sig
   ;;
 
   let mkdir_p p =
-    (* CR-someday amokhov: We should really change [Path.mkdir_p dir] to fail if
-       it turns out that [dir] exists and is not a directory. Even better, make
-       [Path.mkdir_p] return an explicit variant to deal with. *)
-    match Fpath.mkdir_p (Path.to_string p) with
-    | `Created -> ()
-    | `Already_exists ->
-      (match Path.is_directory p with
-       | true -> ()
-       | false ->
-         User_error.raise
-           [ Pp.textf "Please delete file %s manually." (Path.to_string_maybe_quoted p) ])
+    match Fpath.mkdir_p_strict (Path.to_string p) with
+    | `Created | `Already_exists -> ()
+    | `Not_a_dir ->
+      User_error.raise
+        [ Pp.textf "Please delete file %s manually." (Path.to_string_maybe_quoted p) ]
   ;;
 end
 

otherlibs/stdune/src/fpath.ml

@@ -57,6 +57,15 @@ let rec mkdir_p ?perms t_s =
            Code_error.raise "failed to create parent directory" [ "t_s", Dyn.string t_s ]))
 ;;
 
+let mkdir_p_strict ?perms t_s =
+  match mkdir_p ?perms t_s with
+  | `Created -> `Created
+  | `Already_exists ->
+    (match (Unix.stat t_s).st_kind with
+     | S_DIR -> `Already_exists
+     | _ -> `Not_a_dir)
+;;
+
 let link src dst =
   match Unix.link src dst with
   | exception Unix.Unix_error (Unix.EUNKNOWNERR -1142, syscall, arg)

otherlibs/stdune/src/fpath.mli

@@ -16,6 +16,7 @@ type mkdir_p_result =
 
 val dyn_of_mkdir_p_result : mkdir_p_result -> Dyn.t
 val mkdir_p : ?perms:int -> string -> mkdir_p_result
+val mkdir_p_strict : ?perms:int -> string -> [ mkdir_p_result | `Not_a_dir ]
 
 (** [link src dst] creates a hardlink from [src] to [dst]. *)
 val link : string -> string -> unit