fix: allow mappers to override root types (Query, Mutation, Subscription) (#10512)

* fix: allow mappers to override root types (Query, Mutation, Subscription)

Previously, root types were checked before mappers, which prevented
mappers from working on root types. This fix moves the mapper check
before the root type check, allowing mappers to override rootValueType
when configured.

This is particularly useful when a GraphQL schema has a root Subscription
type that is also a regular object type (e.g., Stripe subscription),
and you want to use a custom mapper type instead of the default
Record<PropertyKey, never>.

* chore: add changeset for mapper fix

Author: realies

.changeset/few-worms-talk.md

@@ -0,0 +1,7 @@
+---
+"@graphql-codegen/visitor-plugin-common": patch
+---
+
+fix: allow mappers to override root types (Query, Mutation, Subscription)
+
+Previously, mappers configured for root types were ignored because root types were checked before mappers. This fix moves the mapper check before the root type check, allowing mappers to override `rootValueType` when configured.

packages/plugins/other/visitor-plugin-common/src/base-resolvers-visitor.ts

@@ -971,15 +971,20 @@ export class BaseResolversVisitor<
       const isScalar = this.config.scalars[typeName];
       const hasDefaultMapper = !!this.config.defaultMapper?.type;
 
+      // Check for mappers first, even for root types, to allow overriding rootValueType
+      if (isMapped && this.config.mappers[typeName].type && !hasPlaceholder(this.config.mappers[typeName].type)) {
+        this.markMapperAsUsed(typeName);
+        prev[typeName] = applyWrapper(this.config.mappers[typeName].type);
+
+        return prev;
+      }
+
       if (isRootType) {
         prev[typeName] = applyWrapper(this.config.rootValueType.type);
 
         return prev;
       }
-      if (isMapped && this.config.mappers[typeName].type && !hasPlaceholder(this.config.mappers[typeName].type)) {
-        this.markMapperAsUsed(typeName);
-        prev[typeName] = applyWrapper(this.config.mappers[typeName].type);
-      } else if (isEnumType(schemaType) && this.config.enumValues[typeName]) {
+      if (isEnumType(schemaType) && this.config.enumValues[typeName]) {
         const isExternalFile = !!this.config.enumValues[typeName].sourceFile;
         prev[typeName] = isExternalFile
           ? this.convertName(this.config.enumValues[typeName].typeIdentifier, {