simplify parsing of record rest

Author: tsnobip

compiler/syntax/src/res_core.ml

@@ -1456,13 +1456,14 @@ and parse_record_pattern_row p =
   | DotDotDot -> (
     Parser.next p;
     let start_pos = p.Parser.start_pos in
-    match p.Parser.token with
-    | Uident _ ->
-      (* ...ModulePath.t<'a> as name *)
-      let type_path = parse_value_path p in
-      let type_loc = type_path.loc in
-      let type_args = parse_type_constructor_args ~constr_name:type_path p in
-      let core_type = Ast_helper.Typ.constr ~loc:type_loc type_path type_args in
+    let has_type_annotation =
+      Parser.lookahead p (fun p ->
+          ignore (parse_atomic_typ_expr ~attrs:[] p);
+          p.token = As)
+    in
+    if has_type_annotation then (
+      (* ...TypeAnnotation<'a> as name *)
+      let core_type = parse_atomic_typ_expr ~attrs:[] p in
       Parser.expect As p;
       let name_start = p.start_pos in
       let name =
@@ -1480,48 +1481,20 @@ and parse_record_pattern_row p =
           (Ast_helper.Pat.var ~loc:name.loc name)
           core_type
       in
-      Some (false, PatRest rest_pat)
-    | Lident ident ->
-      Parser.next p;
-      if p.Parser.token = As || p.Parser.token = Token.LessThan then (
-        (* ...typeName<'a> as name *)
-        let type_path =
-          Location.mkloc (Longident.Lident ident)
-            (mk_loc start_pos p.prev_end_pos)
-        in
-        let type_loc = type_path.loc in
-        let type_args = parse_type_constructor_args ~constr_name:type_path p in
-        let core_type =
-          Ast_helper.Typ.constr ~loc:type_loc type_path type_args
-        in
-        Parser.expect As p;
-        let name_start = p.start_pos in
-        let name =
-          match p.token with
-          | Lident id ->
-            Parser.next p;
-            Location.mkloc id (mk_loc name_start p.prev_end_pos)
-          | _ ->
-            Parser.err p (Diagnostics.unexpected p.token p.breadcrumbs);
-            Location.mkloc "_" (mk_loc name_start p.prev_end_pos)
-        in
-        let rest_loc = mk_loc start_pos p.prev_end_pos in
-        let rest_pat =
-          Ast_helper.Pat.constraint_ ~loc:rest_loc ~attrs
-            (Ast_helper.Pat.var ~loc:name.loc name)
-            core_type
-        in
-        Some (false, PatRest rest_pat))
-      else
+      Some (false, PatRest rest_pat))
+    else
+      match p.Parser.token with
+      | Lident ident ->
         (* ...name (no type annotation) *)
+        Parser.next p;
         let loc = mk_loc start_pos p.prev_end_pos in
         let rest_pat =
           Ast_helper.Pat.var ~loc ~attrs (Location.mkloc ident loc)
         in
         Some (false, PatRest rest_pat)
-    | _ ->
-      (* Fallback: treat as old-style spread (error) *)
-      Some (true, PatField (parse_record_pattern_row_field ~attrs p)))
+      | _ ->
+        (* Fallback: treat as old-style spread (error) *)
+        Some (true, PatField (parse_record_pattern_row_field ~attrs p)))
   | Uident _ | Lident _ ->
     Some (false, PatField (parse_record_pattern_row_field ~attrs p))
   | Question -> (