fix: Support prefixes other than a/ & b/ when modifying files (#1…

…0899)

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

src/dune_patch/dune_patch.ml

@@ -79,7 +79,10 @@ let patches_of_string patch_string =
           ( Path.Local.split_first_component old_path
           , Path.Local.split_first_component new_path )
         with
-        | Some ("a", _old_path), Some ("b", new_path) -> new_path, 1
+        | Some (_, old_path), Some (_, new_path)
+          when Path.Local.equal old_path new_path && not (Path.Local.is_root new_path) ->
+          (* suffixes are the same and not empty *)
+          new_path, 1
         | _, _ -> new_path, 0
       in
       (* Replace file *)

test/expect-tests/dune_patch/dune_patch_tests.ml

@@ -239,14 +239,9 @@ let%expect_test "patching a file without prefix" =
 ;;
 
 let%expect_test "patching files with freestyle prefix" =
-  try
-    test [ "foo.ml", "This is wrong\n" ] ("foo.patch", random_prefix);
-    check "foo.ml";
-    [%expect.unreachable]
-  with
-  | Dune_util.Report_error.Already_reported ->
-    print_endline @@ normalize_error_path [%expect.output];
-    [%expect {| Error: foo.ml: No such file or directory |}]
+  test [ "foo.ml", "This is wrong\n" ] ("foo.patch", random_prefix);
+  check "foo.ml";
+  [%expect {| This is right |}]
 ;;
 
 let%expect_test "patching files with spaces" =