feat: deep merge resolvers

.changeset/cold-dancers-call.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": minor
+---
+
+`createProxiedSchema` deep merges resolvers by default, can be opted out of with `mergeResolvers: false`

package.json

@@ -111,6 +111,7 @@
     "@babel/parser": "7.24.1",
     "@changesets/changelog-github": "0.5.0",
     "@changesets/cli": "2.27.1",
+    "@graphql-tools/merge": "^9.0.3",
     "@graphql-tools/schema": "10.0.3",
     "@graphql-tools/utils": "10.0.13",
     "@microsoft/api-extractor": "7.42.3",

src/testing/core/__tests__/createProxiedSchema.test.tsx

@@ -346,7 +346,7 @@ describe("schema proxy", () => {
     unmount();
   });
 
-  it("does not pollute the original schema", async () => {
+  it("schema.fork does not pollute the original schema", async () => {
     const Profiler = createDefaultProfiler<ViewerQueryData>();
 
     using _fetch = createMockFetch(schema);
@@ -861,6 +861,7 @@ describe("schema proxy", () => {
       },
       Book: {
         __resolveType: (obj) => {
+          console.log(obj);
           if ("text" in obj) {
             return "TextBook";
           }
@@ -876,10 +877,9 @@ describe("schema proxy", () => {
       resolvers: {
         Query: {
           viewer: () => ({
-            name: "Virginia",
             book: {
               colors: ["red", "blue", "green"],
-              title: "The Book",
+              title: "A New Book",
             },
           }),
         },
@@ -997,7 +997,7 @@ describe("schema proxy", () => {
             colors: ["red", "blue", "green"],
             id: "1",
             publishedAt: "2024-01-01",
-            title: "The Book",
+            title: "A New Book",
           },
         },
       });
@@ -1020,12 +1020,15 @@ describe("schema proxy", () => {
             colors: ["red", "blue", "green"],
             id: "1",
             publishedAt: "2024-01-01",
-            title: "The Book",
+            title: "A New Book",
           },
         },
       });
     }
 
     unmount();
   });
+  it.todo("add test for reset");
+  it.todo("add test for mergeResolvers: false");
+  it.todo("add test for mergeResolvers: true");
 });

src/testing/core/createProxiedSchema.ts

@@ -1,6 +1,6 @@
-import { addResolversToSchema } from "@graphql-tools/schema";
 import type { GraphQLSchema } from "graphql";
-
+import { addResolversToSchema } from "@graphql-tools/schema";
+import { mergeResolvers } from "@graphql-tools/merge";
 import type { Resolvers } from "../../core/types.js";
 
 type ProxiedSchema = GraphQLSchema & ProxiedSchemaFns;
@@ -11,6 +11,10 @@ interface ProxiedSchemaFns {
   reset: () => void;
 }
 
+type CreateProxiedSchemaOptions = {
+  mergeResolvers: boolean;
+};
+
 /**
  * A function that creates a [Proxy object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy)
  * around a given `schema` with `resolvers`. This proxied schema can be used to
@@ -45,7 +49,10 @@ interface ProxiedSchemaFns {
  */
 const createProxiedSchema = (
   schemaWithMocks: GraphQLSchema,
-  resolvers: Resolvers
+  resolvers: Resolvers,
+  options: CreateProxiedSchemaOptions = {
+    mergeResolvers: true,
+  }
 ): ProxiedSchema => {
   let targetResolvers = { ...resolvers };
   let targetSchema = addResolversToSchema({
@@ -55,7 +62,12 @@ const createProxiedSchema = (
 
   const fns: ProxiedSchemaFns = {
     add: ({ resolvers: newResolvers }) => {
-      targetResolvers = { ...targetResolvers, ...newResolvers };
+      // @ts-ignore TODO(fixme): IResolvers type does not play well with our Resolvers
+      targetResolvers =
+        options.mergeResolvers ?
+          mergeResolvers([targetResolvers, newResolvers])
+        : { ...targetResolvers, ...newResolvers };
+
       targetSchema = addResolversToSchema({
         schema: targetSchema,
         resolvers: targetResolvers,
@@ -65,7 +77,11 @@ const createProxiedSchema = (
     },
 
     fork: ({ resolvers: newResolvers } = {}) => {
-      return createProxiedSchema(targetSchema, newResolvers ?? targetResolvers);
+      return createProxiedSchema(
+        targetSchema,
+        newResolvers ?? targetResolvers,
+        options
+      );
     },
 
     reset: () => {