Fix Parmatch crash on empty record head patterns (#8246)

* Fix Parmatch crash on empty record head patterns

* Simpler test

Author: fhammerschmidt

compiler/ml/parmatch.ml

@@ -512,6 +512,7 @@ let extract_fields omegas arg =
 
 let all_record_args lbls =
   match lbls with
+  | [] -> []
   | (_, {lbl_all}, _, opt) :: _ ->
     let t =
       Array.map
@@ -560,7 +561,6 @@ let all_record_args lbls =
         t.(lbl.lbl_pos) <- x)
       lbls;
     Array.to_list t
-  | _ -> fatal_error "Parmatch.all_record_args"
 
 (* Build argument list when p2 >= p1, where p1 is a simple pattern *)
 let rec simple_match_args p1 p2 =

tests/tests/src/parmatch_empty_record_pattern_test.mjs

@@ -0,0 +1,13 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+let match = {};
+
+let emptyDictPatternShouldCompile;
+
+emptyDictPatternShouldCompile = typeof match === "object" && match !== null && !Array.isArray(match);
+
+export {
+  emptyDictPatternShouldCompile,
+}
+/* emptyDictPatternShouldCompile Not a pure module */

tests/tests/src/parmatch_empty_record_pattern_test.res

@@ -0,0 +1,4 @@
+let emptyDictPatternShouldCompile = switch JSON.Object(dict{}) {
+| JSON.Object(dict{}) => true
+| _ => false
+}