Clarify tag/as conflict error message by using field name from type instead of only showing runtime name

Author: mediremi

compiler/ml/ast_untagged_variants.ml

@@ -57,7 +57,7 @@ type error =
   | Duplicated_bs_as
   | InvalidVariantTagAnnotation
   | InvalidUntaggedVariantDefinition of untagged_error
-  | TagFieldNameConflict of string * string
+  | TagFieldNameConflict of string * string * string
 exception Error of Location.t * error
 
 let report_error ppf =
@@ -91,11 +91,12 @@ let report_error ppf =
       | DuplicateLiteral s -> "Duplicate literal " ^ s ^ "."
       | ConstructorMoreThanOneArg name ->
         "Constructor " ^ name ^ " has more than one argument.")
-  | TagFieldNameConflict (constructor_name, field_name) ->
+  | TagFieldNameConflict (constructor_name, field_name, runtime_value) ->
     fprintf ppf
-      "Constructor %s: the @tag name \"%s\" conflicts with inline record field \
-       \"%s\". Use a different @tag name or rename the field."
-      constructor_name field_name field_name
+      "Constructor %s: the @tag name \"%s\" conflicts with the runtime value \
+       of inline record field \"%s\". Use a different @tag name or rename the \
+       field."
+      constructor_name runtime_value field_name
 
 (* Type of the runtime representation of an untagged block (case with payoad) *)
 type block_type =
@@ -471,28 +472,30 @@ let names_from_type_variant ?(is_untagged_def = false) ~env
 let check_tag_field_conflicts (cstrs : Types.constructor_declaration list) =
   List.iter
     (fun (cstr : Types.constructor_declaration) ->
-      (* Get the effective tag name - either explicit @tag or constructor name *)
-      let tag_name =
+      let constructor_name = Ident.name cstr.cd_id in
+      let effective_tag_name =
         match process_tag_name cstr.cd_attributes with
         | Some explicit_tag -> explicit_tag
-        | None -> Ident.name cstr.cd_id (* Default to constructor name *)
+        | None -> constructor_name
       in
       match cstr.cd_args with
       | Cstr_record fields ->
         List.iter
           (fun (field : Types.label_declaration) ->
-            (* Get the effective field name in JavaScript output *)
+            let field_name = Ident.name field.ld_id in
             let effective_field_name =
               match process_tag_type field.ld_attributes with
-              | Some (String as_name) -> as_name (* Use @as name if present *)
-              | _ -> Ident.name field.ld_id (* Otherwise use field name *)
+              | Some (String as_name) -> as_name
+              (* @as payload types other than string have no effect on record fields *)
+              | Some _ | None -> field_name
             in
             (* Check if effective field name conflicts with tag *)
-            if effective_field_name = tag_name then
+            if effective_field_name = effective_tag_name then
               raise
                 (Error
                    ( cstr.cd_loc,
-                     TagFieldNameConflict (Ident.name cstr.cd_id, tag_name) )))
+                     TagFieldNameConflict
+                       (constructor_name, field_name, effective_field_name) )))
           fields
       | _ -> ())
     cstrs