improve error message when an object is passed where a record is expected

Author: zth

compiler/ml/error_message_utils.ml

@@ -57,7 +57,15 @@ let error_expected_type_text ppf type_clash_context =
     fprintf ppf "But this function is expecting you to return:"
   | _ -> fprintf ppf "But it's expected to have type:"
 
-let print_extra_type_clash_help ppf trace type_clash_context =
+let is_record_type ~extract_concrete_typedecl ~env ty =
+  try
+    match extract_concrete_typedecl env ty with
+    | _, _, {Types.type_kind = Type_record _; _} -> true
+    | _ -> false
+  with _ -> false
+
+let print_extra_type_clash_help ~extract_concrete_typedecl ~env ppf trace
+    type_clash_context =
   match (type_clash_context, trace) with
   | Some (MathOperator {for_float; operator; is_constant}), _ -> (
     let operator_for_other_type =
@@ -176,6 +184,15 @@ let print_extra_type_clash_help ppf trace type_clash_context =
       \  - If you don't care about the result of this expression, you can \
        assign it to @{<info>_@} via @{<info>let _ = ...@} or pipe it to \
        @{<info>ignore@} via @{<info>expression->ignore@}\n\n"
+  | _, [({desc = Tobject _}, _); (({Types.desc = Tconstr _} as t1), _)]
+    when is_record_type ~extract_concrete_typedecl ~env t1 ->
+    fprintf ppf
+      "\n\n\
+      \  You're passing a @{<error>ReScript object@} where a @{<info>record@} \
+       is expected. \n\n\
+      \  - Did you mean to pass a record instead of an object? Objects are \
+       written with quoted keys, and records with unquoted keys. Remove the \
+       quotes from the object keys to pass it as a record instead of object. \n\n"
   | _ -> ()
 
 let type_clash_context_from_function sexp sfunct =

compiler/ml/typecore.ml

@@ -814,7 +814,8 @@ let print_expr_type_clash ?type_clash_context env trace ppf =
         | ppf -> error_type_text ppf type_clash_context)
       (function
         | ppf -> error_expected_type_text ppf type_clash_context);
-    print_extra_type_clash_help ppf trace type_clash_context;
+    print_extra_type_clash_help ~extract_concrete_typedecl ~env ppf trace
+      type_clash_context;
     show_extra_help ppf env trace
 
 let report_arity_mismatch ~arity_a ~arity_b ppf =

tests/build_tests/super_errors/expected/object_passed_when_record_expected.res.expected

@@ -0,0 +1,15 @@
+
+  We've found a bug for you!
+  /.../fixtures/object_passed_when_record_expected.res:4:14-26
+
+  2 │ type xx = array<x>
+  3 │ 
+  4 │ let x: xx = [{"one": true}]
+  5 │ 
+
+  This has type: {"one": bool}
+  But it's expected to have type: x
+
+  You're passing a ReScript object where a record is expected. 
+
+  - Did you mean to pass a record instead of an object? Objects are written with quoted keys, and records with unquoted keys. Remove the quotes from the object keys to pass it as a record instead of object.

tests/build_tests/super_errors/fixtures/object_passed_when_record_expected.res

@@ -0,0 +1,4 @@
+type x = {one: bool}
+type xx = array<x>
+
+let x: xx = [{"one": true}]