fix __typename @tag conflict

Author: zth

compiler/crates/relay-typegen/src/rescript.rs

@@ -1475,6 +1475,12 @@ fn write_object_definition_body(
     let mut has_printed_keys = FnvHashSet::default();
 
     object.values.iter().for_each(|prop| {
+        // If this is the inline object that forms the payload of a union
+        // variant tagged by __typename, do not also emit a __typename field
+        // inside the object payload.
+        if object.is_union_member_inline_obj && &*prop.key == "__typename" {
+            return;
+        }
         if has_printed_keys.contains(&prop.key) {
             return;
         } else {

compiler/test-project-res-preloadable/src/UserAvatar.res

@@ -1,6 +1,6 @@
 module Fragment = %relay(`
   fragment UserAvatar_user on User {
     avatarUrl
-    ...UserName_user @codesplit
+    ...UserName_user @codesplit @alias
   }
 `)

compiler/test-project-res-preloadable/src/__generated__/RelaySchemaAssets_graphql.res

@@ -9,7 +9,7 @@ module Query = %relay(`
 
 module Query = %relay(`
     query TestUnionFragmentExhaustiveQuery {
-      member(id: "123") @exhaustive {
+      member(id: "123") {
         ... on User {
           firstName
         }