Change Process.run's ~dir argument to use Path.t

This also requires Scheduler.with_chdir to use Path.t as well

src/action.ml

@@ -735,7 +735,7 @@ let exec_run_direct ~ectx ~dir ~env ~stdout_to ~stderr_to prog args =
      invalid_prefix ("_build/" ^ target.name);
      invalid_prefix ("_build/install/" ^ target.name);
   end;
-  Process.run Strict ~dir:(Path.to_string dir) ~env
+  Process.run Strict ~dir ~env
     ~stdout_to ~stderr_to
     ~purpose:ectx.purpose
     (Path.reach_for_running ~from:dir prog) args

src/jbuild_load.ml

@@ -147,7 +147,7 @@ end
            in
          ]}
       *)
-      Process.run Strict ~dir:(Path.to_string dir)
+      Process.run Strict ~dir
         ~env:context.env
         (Path.to_string context.ocaml)
         args

src/print_diff.ml

@@ -9,9 +9,9 @@ let print path1 path2 =
       Path.extract_build_context_dir path2
     with
     | Some (dir1, f1), Some (dir2, f2) when dir1 = dir2 ->
-      (Path.to_string dir1, Path.to_string f1, Path.to_string f2)
+      (dir1, Path.to_string f1, Path.to_string f2)
     | _ ->
-      (".", Path.to_string path1, Path.to_string path2)
+      (Path.root, Path.to_string path1, Path.to_string path2)
   in
   let loc = Loc.in_file file1 in
   let fallback () =
@@ -38,10 +38,10 @@ let print path1 path2 =
     Process.run ~dir ~env:Env.initial Strict (Path.to_string sh) [arg; cmd]
     >>= fun () ->
     die "command reported no differences: %s"
-      (if dir = "." then
+      (if Path.is_root dir then
          cmd
        else
-         sprintf "cd %s && %s" (quote_for_shell dir) cmd)
+         sprintf "cd %s && %s" (quote_for_shell (Path.to_string dir)) cmd)
   | None ->
     match Bin.which "patdiff" with
     | None -> normal_diff ()

src/process.ml

@@ -121,7 +121,7 @@ module Fancy = struct
     let s =
       match dir with
       | None -> s
-      | Some dir -> sprintf "(cd %s && %s)" dir s
+      | Some dir -> sprintf "(cd %s && %s)" (Path.to_string dir) s
     in
     match stdout_to, stderr_to with
     | (File fn1 | Opened_file { filename = fn1; _ }),
@@ -216,8 +216,12 @@ let run_internal ?dir ?(stdout_to=Terminal) ?(stderr_to=Terminal) ~env ~purpose
   let display = Scheduler.display scheduler in
   let dir =
     match dir with
-    | Some "." -> None
-    | _ -> dir
+    | Some p ->
+      if Path.is_root p then
+        None
+      else
+        Some p
+    | None -> dir
   in
   let id = gen_id () in
   let ok_codes = accepted_codes fail_mode in
@@ -344,7 +348,7 @@ let run_capture_line ?dir ~env ?(purpose=Internal_job) fail_mode prog args =
         let s = String.concat (prog :: args) ~sep:" " in
         match dir with
         | None -> s
-        | Some dir -> sprintf "cd %s && %s" dir s
+        | Some dir -> sprintf "cd %s && %s" (Path.to_string dir) s
       in
       match l with
       | [] ->

src/process.mli

@@ -38,7 +38,7 @@ type purpose =
 
 (** [run ?dir ?stdout_to prog args] spawns a sub-process and wait for its termination *)
 val run
-  :  ?dir:string
+  :  ?dir:Path.t
   -> ?stdout_to:std_output_to
   -> ?stderr_to:std_output_to
   -> env:Env.t
@@ -50,7 +50,7 @@ val run
 
 (** Run a command and capture its output *)
 val run_capture
-  :  ?dir:string
+  :  ?dir:Path.t
   -> env:Env.t
   -> ?purpose:purpose
   -> (string, 'a) failure_mode
@@ -58,7 +58,7 @@ val run_capture
   -> string list
   -> 'a Fiber.t
 val run_capture_line
-  :  ?dir:string
+  :  ?dir:Path.t
   -> env:Env.t
   -> ?purpose:purpose
   -> (string, 'a) failure_mode
@@ -66,7 +66,7 @@ val run_capture_line
   -> string list
   -> 'a Fiber.t
 val run_capture_lines
-  :  ?dir:string
+  :  ?dir:Path.t
   -> env:Env.t
   -> ?purpose:purpose
   -> (string list, 'a) failure_mode

src/scheduler.ml

@@ -72,7 +72,7 @@ let log t = t.log
 let display t = t.display
 
 let with_chdir t ~dir ~f =
-  Sys.chdir dir;
+  Sys.chdir (Path.to_string dir);
   protectx () ~finally:(fun () -> Sys.chdir t.original_cwd) ~f
 
 let hide_status_line s =

src/scheduler.mli

@@ -1,5 +1,7 @@
 (** Scheduling *)
 
+open Stdune
+
 (** [go ?log ?config ?gen_status_line fiber] runs the following fiber until it
     terminates. [gen_status_line] is used to print a status line when [config.display =
     Progress]. *)
@@ -27,7 +29,7 @@ val wait_for_available_job : unit -> t Fiber.t
 val log : t -> Log.t
 
 (** Execute the given callback with current directory temporarily changed *)
-val with_chdir : t -> dir:string -> f:(unit -> 'a) -> 'a
+val with_chdir : t -> dir:Path.t -> f:(unit -> 'a) -> 'a
 
 (** Display mode for this scheduler *)
 val display : t -> Config.Display.t