fix(stitch): add __typename for mutations (#2467)

* fix(stitch): add __typename for mutations

* Create giant-cooks-melt.md

Author: dimatill

.changeset/giant-cooks-melt.md

@@ -0,0 +1,7 @@
+---
+"@graphql-tools/stitch": patch
+---
+
+fix(stitch): add __typename for mutations
+
+fix related to #2349

packages/stitch/src/stitchingInfo.ts

@@ -233,7 +233,7 @@ export function completeStitchingInfo(
   schema: GraphQLSchema
 ): StitchingInfo {
   const selectionSetsByType = Object.create(null);
-  [schema.getQueryType(), schema.getMutationType].forEach(rootType => {
+  [schema.getQueryType(), schema.getMutationType()].forEach(rootType => {
     if (rootType) {
       selectionSetsByType[rootType.name] = parseSelectionSet('{ __typename }', { noLocation: true });
     }

packages/stitch/tests/nestedRootTypes.test.ts

@@ -1,5 +1,5 @@
-import { makeExecutableSchema } from "@graphql-tools/schema";
-import { stitchSchemas } from "@graphql-tools/stitch";
+import { makeExecutableSchema } from '@graphql-tools/schema';
+import { stitchSchemas } from '@graphql-tools/stitch';
 import { graphql } from 'graphql';
 
 describe('nested root types', () => {
@@ -9,12 +9,20 @@ describe('nested root types', () => {
         schema1Boolean: Boolean
         schema1Query: Query
       }
+      type Mutation {
+        schema1Boolean: Boolean
+        schema1Mutation: Mutation
+      }
     `,
     resolvers: {
       Query: {
         schema1Boolean: () => true,
         schema1Query: () => ({}),
       },
+      Mutation: {
+        schema1Boolean: () => true,
+        schema1Mutation: () => ({}),
+      },
     },
   });
 
@@ -24,20 +32,28 @@ describe('nested root types', () => {
         schema2Boolean: Boolean
         schema2Query: Query
       }
+      type Mutation {
+        schema2Boolean: Boolean
+        schema2Mutation: Mutation
+      }
     `,
     resolvers: {
       Query: {
         schema2Boolean: () => true,
         schema2Query: () => ({}),
       },
+      Mutation: {
+        schema2Boolean: () => true,
+        schema2Mutation: () => ({}),
+      },
     },
   });
 
   const stitchedSchema = stitchSchemas({
     subschemas: [schema1, schema2],
   });
 
-  it('works to nest root field', async () => {
+  it('works to nest Query', async () => {
     const query = `
       query {
         schema1Query {
@@ -75,4 +91,43 @@ describe('nested root types', () => {
     const result = await graphql(stitchedSchema, query);
     expect(result).toEqual(expectedResult);
   });
+
+  it('works to nest Mutation', async () => {
+    const mutation = `
+      mutation {
+        schema1Mutation {
+          schema1Boolean
+          schema2Mutation {
+            schema1Boolean
+          }
+        }
+        schema2Mutation {
+          schema2Boolean
+          schema1Mutation {
+            schema2Boolean
+          }
+        }
+      }
+    `;
+
+    const expectedResult = {
+      data: {
+        schema1Mutation: {
+          schema1Boolean: true,
+          schema2Mutation: {
+            schema1Boolean: true,
+          },
+        },
+        schema2Mutation: {
+          schema2Boolean: true,
+          schema1Mutation: {
+            schema2Boolean: true,
+          },
+        },
+      },
+    };
+
+    const result = await graphql(stitchedSchema, mutation);
+    expect(result).toEqual(expectedResult);
+  });
 });