bugfix: Add <DkMLHome>/usr/bin to PATH

Only for precompiled binaries which are already in usr/bin.

+ Add tracing to autodetect compiler.
+bugfix: Detect installation prefix now that precompiled are in
usr/bin not bin/. Needs two directories up not one.

Part of diskuv/dkml-installer-ocaml#77

src/with-dkml/cmdline.ml

@@ -142,10 +142,10 @@ let when_path_exists_set_env ~envvar path =
 
 let set_precompiled_env abs_cmd_p =
   let ( let* ) = Rresult.R.( >>= ) in
-  (* Installation prefix *)
-  let prefix_p = Fpath.(parent (parent abs_cmd_p)) in
+  (* Installation prefix. Example: <prefix>/usr/bin/utop -> <prefix> *)
+  let prefix_p = Fpath.(abs_cmd_p |> parent |> parent |> parent) in
   let bc_p = Fpath.(prefix_p / "desktop" / "bc") in
-  let bc_bin_p = Fpath.(bc_p / "bin") in
+  let bc_usr_bin_p = Fpath.(bc_p / "usr" / "bin") in
   let bc_ocaml_lib_p = Fpath.(bc_p / "lib" / "ocaml") in
   let bc_ocaml_stublibs_p = Fpath.(bc_ocaml_lib_p / "stublibs") in
   let bc_stublibs_p = Fpath.(bc_p / "lib" / "stublibs") in
@@ -187,7 +187,9 @@ let set_precompiled_env abs_cmd_p =
       in
       (* Dune requires ocamlc in the PATH. It should already be present
          but just in case put the bytecode executables in the PATH *)
-      let* () = when_dir_exists_prepend_pathlike_env ~envvar:"PATH" bc_bin_p in
+      let* () =
+        when_dir_exists_prepend_pathlike_env ~envvar:"PATH" bc_usr_bin_p
+      in
       Ok ()
   | _ ->
       (* In an Opam switch

src/with-dkml/with_dkml.ml

@@ -286,7 +286,14 @@ let set_msvc_entries cache_keys =
           let dash =
             Fpath.(msys2_dir / "usr" / "bin" / "dash.exe" |> to_string)
           in
-          let cmd = Cmd.(v dash % Fpath.to_string tmp_sh_file) in
+          let extra_options =
+            match Logs.level () with
+            | Some Debug -> Cmd.(v "-x")
+            | _ -> Cmd.empty
+          in
+          let cmd =
+            Cmd.(v dash %% extra_options % Fpath.to_string tmp_sh_file)
+          in
           (OS.Cmd.run_status cmd >>= function
            | `Exited status ->
                if status <> 0 then