Fix Unknow type merge bug on overloaded types (#6494)

* Fix Unknow type bug on overloaded types

* check args too

spec/ParseGraphQLServer.spec.js

@@ -10821,11 +10821,11 @@ describe('ParseGraphQLServer', () => {
         expect(result2.data.someClass.name).toEqual('aname');
         expect(result.data.someClass.language).toEqual('fr');
         const result3 = await apolloClient.mutate({
-          variables: { id: obj.id, name: 'anewname' },
+          variables: { id: obj.id, name: 'anewname', type: 'human' },
           mutation: gql`
-            mutation someClass($id: ID!, $name: String!) {
+            mutation someClass($id: ID!, $name: String!, $type: TypeEnum!) {
               updateSomeClass(
-                input: { id: $id, fields: { name: $name, type: human } }
+                input: { id: $id, fields: { name: $name, type: $type } }
               ) {
                 someClass {
                   nameUpperCase

src/GraphQL/ParseGraphQLSchema.js

@@ -211,7 +211,33 @@ class ParseGraphQLSchema {
             const autoGraphQLSchemaType = this.graphQLAutoSchema.getType(
               customGraphQLSchemaType.name
             );
-            if (autoGraphQLSchemaType) {
+            if (
+              autoGraphQLSchemaType &&
+              typeof customGraphQLSchemaType.getFields === 'function'
+            ) {
+              const findAndAddLastType = type => {
+                if (type.name) {
+                  if (!this.graphQLAutoSchema.getType(type)) {
+                    // To avoid schema stitching (Unknow type) bug on variables
+                    // transfer the final type to the Auto Schema
+                    this.graphQLAutoSchema._typeMap[type.name] = type;
+                  }
+                } else {
+                  if (type.ofType) {
+                    findAndAddLastType(type.ofType);
+                  }
+                }
+              };
+              Object.values(customGraphQLSchemaType.getFields()).forEach(
+                field => {
+                  findAndAddLastType(field.type);
+                  if (field.args) {
+                    field.args.forEach(arg => {
+                      findAndAddLastType(arg.type);
+                    });
+                  }
+                }
+              );
               autoGraphQLSchemaType._fields = {
                 ...autoGraphQLSchemaType._fields,
                 ...customGraphQLSchemaType._fields,