fix: correctly list vcs files in subdirectory

Signed-off-by: Rudi Grinberg <[email protected]>

Author: rgrinberg

src/dune_vcs/vcs.ml

@@ -182,8 +182,27 @@ let files =
   in
   let f run args t =
     let open Fiber.O in
-    let+ l = run t args in
-    List.map l ~f:Path.Source.of_string
+    let f =
+      let prefix =
+        Path.to_absolute_filename t.root |> Path.External.of_string |> Path.external_
+      in
+      let source_root =
+        Path.to_absolute_filename (Path.source Path.Source.root)
+        |> Path.External.of_string
+        |> Path.external_
+      in
+      match Path.drop_prefix source_root ~prefix with
+      | None -> fun p -> Some (Path.Source.of_string p)
+      | Some prefix ->
+        fun p ->
+          (match
+             let p = Path.Local.of_string p in
+             Path.Local.descendant p ~of_:prefix
+           with
+           | None -> None
+           | Some p -> Some (Path.Source.of_local p))
+    in
+    run t args >>| List.filter_map ~f
   in
   Staged.unstage
   @@ make_fun

test/blackbox-tests/test-cases/subst/git-subfolder.t

@@ -14,8 +14,3 @@ Regression test for https://github.com/ocaml/dune/issues/11045
   $ git add -A && git commit --quiet --message "Initial commit"
   $ cd subfolder
   $ dune subst
-  File ".", line 1, characters 0-0:
-  Error: There is no dune-project file in the current directory, please add one
-  with a (name <name>) field in it.
-  Hint: 'dune subst' must be executed from the root of the project.
-  [1]