Improve return type of customFormatErrorFn

integrationTests/ts/package.json

@@ -5,7 +5,7 @@
   "dependencies": {
     "@types/node": "14.0.13",
     "express-graphql": "file:../express-graphql.tgz",
-    "graphql": "14.6.0",
+    "graphql": "14.7.0",
     "typescript-3.4": "npm:typescript@3.4.x",
     "typescript-3.5": "npm:typescript@3.5.x",
     "typescript-3.6": "npm:typescript@3.6.x",

package.json

@@ -79,7 +79,7 @@
     "express": "4.17.1",
     "flow-bin": "0.128.0",
     "graphiql": "1.0.3",
-    "graphql": "15.2.0",
+    "graphql": "15.3.0",
     "mocha": "8.0.1",
     "multer": "1.4.2",
     "nyc": "15.1.0",
@@ -95,6 +95,6 @@
     "unfetch": "4.1.0"
   },
   "peerDependencies": {
-    "graphql": "^14.6.0 || ^15.0.0"
+    "graphql": "^14.7.0 || ^15.3.0"
   }
 }

src/__tests__/http-test.ts

@@ -2188,7 +2188,9 @@ function runTests(server: Server) {
         urlString(),
         graphqlHTTP({
           schema: TestSchema,
-          customFormatErrorFn: () => null,
+          customFormatErrorFn: () => ({
+            message: 'Some generic error message.',
+          }),
           extensions({ result }) {
             return { preservedResult: { ...result } };
           },
@@ -2204,7 +2206,7 @@ function runTests(server: Server) {
       expect(response.status).to.equal(200);
       expect(JSON.parse(response.text)).to.deep.equal({
         data: { thrower: null },
-        errors: [null],
+        errors: [{ message: 'Some generic error message.' }],
         extensions: {
           preservedResult: {
             data: { thrower: null },

src/index.d.ts

@@ -11,6 +11,7 @@ import {
   ExecutionArgs,
   ExecutionResult,
   GraphQLError,
+  GraphQLFormattedError,
   GraphQLSchema,
   GraphQLFieldResolver,
   GraphQLTypeResolver,
@@ -90,7 +91,7 @@ export interface OptionsData {
    * fulfilling a GraphQL operation. If no function is provided, GraphQL's
    * default spec-compliant `formatError` function will be used.
    */
-  customFormatErrorFn?: (error: GraphQLError) => unknown;
+  customFormatErrorFn?: (error: GraphQLError) => GraphQLFormattedError;
 
   /**
    * An optional function which will be used to create a document instead of
@@ -102,7 +103,7 @@ export interface OptionsData {
    * `formatError` is deprecated and replaced by `customFormatErrorFn`. It will
    *  be removed in version 1.0.0.
    */
-  formatError?: (error: GraphQLError) => unknown;
+  formatError?: (error: GraphQLError) => GraphQLFormattedError;
 
   /**
    * An optional function for adding additional metadata to the GraphQL response

src/index.js

@@ -9,10 +9,12 @@ import type {
   ValidationContext,
   ExecutionArgs,
   ExecutionResult,
+  FormattedExecutionResult,
   GraphQLError,
   GraphQLSchema,
   GraphQLFieldResolver,
   GraphQLTypeResolver,
+  GraphQLFormattedError,
 } from 'graphql';
 import accepts from 'accepts';
 import httpError from 'http-errors';
@@ -98,7 +100,7 @@ export type OptionsData = {|
    * fulfilling a GraphQL operation. If no function is provided, GraphQL's
    * default spec-compliant `formatError` function will be used.
    */
-  customFormatErrorFn?: (error: GraphQLError) => mixed,
+  customFormatErrorFn?: (error: GraphQLError) => GraphQLFormattedError,
 
   /**
    * An optional function which will be used to create a document instead of
@@ -110,7 +112,7 @@ export type OptionsData = {|
    * `formatError` is deprecated and replaced by `customFormatErrorFn`. It will
    *  be removed in version 1.0.0.
    */
-  formatError?: (error: GraphQLError) => mixed,
+  formatError?: (error: GraphQLError) => GraphQLFormattedError,
 
   /**
    * An optional function for adding additional metadata to the GraphQL response
@@ -380,22 +382,28 @@ export function graphqlHTTP(options: Options): Middleware {
     }
 
     // Format any encountered errors.
-    if (result.errors) {
-      (result: any).errors = result.errors.map(formatErrorFn);
-    }
+    const formattedResult: FormattedExecutionResult = {
+      ...result,
+      errors: result.errors?.map(formatErrorFn),
+    };
 
     // If allowed to show GraphiQL, present it instead of JSON.
     if (showGraphiQL) {
-      return respondWithGraphiQL(response, graphiqlOptions, params, result);
+      return respondWithGraphiQL(
+        response,
+        graphiqlOptions,
+        params,
+        formattedResult,
+      );
     }
 
     // If "pretty" JSON isn't requested, and the server provides a
     // response.json method (express), use that directly.
     // Otherwise use the simplified sendResponse method.
     if (!pretty && typeof response.json === 'function') {
-      response.json(result);
+      response.json(formattedResult);
     } else {
-      const payload = JSON.stringify(result, null, pretty ? 2 : 0);
+      const payload = JSON.stringify(formattedResult, null, pretty ? 2 : 0);
       sendResponse(response, 'application/json', payload);
     }
 
@@ -431,7 +439,7 @@ function respondWithGraphiQL(
   response: $Response,
   options?: GraphiQLOptions,
   params?: GraphQLParams,
-  result?: ExecutionResult,
+  result?: FormattedExecutionResult,
 ): void {
   const data: GraphiQLData = {
     query: params?.query,

src/renderGraphiQL.d.ts

@@ -1,10 +1,10 @@
-import { ExecutionResult } from 'graphql';
+import { FormattedExecutionResult } from 'graphql';
 
 export interface GraphiQLData {
   query?: string | null;
   variables?: { readonly [name: string]: unknown } | null;
   operationName?: string | null;
-  result?: ExecutionResult;
+  result?: FormattedExecutionResult;
 }
 
 export interface GraphiQLOptions {

src/renderGraphiQL.js

@@ -1,12 +1,12 @@
 // @flow strict
 
-import type { ExecutionResult } from 'graphql';
+import type { FormattedExecutionResult } from 'graphql';
 
 export type GraphiQLData = {|
   query?: string | null,
   variables?: { +[name: string]: mixed, ... } | null,
   operationName?: string | null,
-  result?: ExecutionResult,
+  result?: FormattedExecutionResult,
 |};
 
 export type GraphiQLOptions = {|