labelled to optional arg

Author: zth

compiler/ml/error_message_utils.ml

@@ -627,7 +627,12 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
   | ( Some (FunctionArgument {optional = true}),
       Some ({desc = Tconstr (p, _, _)}, _) )
     when Path.same Predef.path_option p ->
-    (* TODO(actions) Prepend with `?` *)
+    Cmt_utils.add_possible_action
+      {
+        loc;
+        action = RewriteArgType {to_type = `Optional};
+        description = "Make argument optional";
+      };
     fprintf ppf
       "@,\
        @,\

tests/build_tests/actions/expected/Actions_MakeArgOptional_applied.res

@@ -0,0 +1,9 @@
+let myFunction = (~name: option<string>=?) => {
+  ignore(name)
+}
+let name = Some("John")
+myFunction(~name?)
+
+/* === AVAILABLE ACTIONS:
+- RewriteArgType(Optional) - Make argument optional
+*/

tests/build_tests/actions/fixtures/Actions_MakeArgOptional.res

@@ -0,0 +1,5 @@
+let myFunction = (~name: option<string>=?) => {
+  ignore(name)
+}
+let name = Some("John")
+myFunction(~name)