add fieldExecutor option to graphql, execute, and subscribe to specif…

…y a custom field executor, export the default field executor for easy wrapping

src/execution/__tests__/executor-test.ts

@@ -1151,6 +1151,29 @@ describe('Execute: Handles basic execution tasks', () => {
     expect(result).to.deep.equal({ data: { foo: null } });
   });
 
+  it('uses a custom field executor', () => {
+    const schema = new GraphQLSchema({
+      query: new GraphQLObjectType({
+        name: 'Query',
+        fields: {
+          foo: { type: GraphQLString },
+        },
+      }),
+    });
+    const document = parse('{ foo }');
+
+    const result = executeSync({
+      schema,
+      document,
+      fieldExecutor() {
+        // For the purposes of test, just return the name of the field!
+        return 'foo';
+      },
+    });
+
+    expect(result).to.deep.equal({ data: { foo: 'foo' } });
+  });
+
   it('uses a custom field resolver', () => {
     const schema = new GraphQLSchema({
       query: new GraphQLObjectType({

src/execution/execute.ts

@@ -102,9 +102,18 @@ export interface ExecutionContext {
   variableValues: { [variable: string]: unknown };
   fieldResolver: GraphQLFieldResolver<any, any>;
   typeResolver: GraphQLTypeResolver<any, any>;
+  fieldExecutor: GraphQLFieldExecutor;
   errors: Array<GraphQLError>;
 }
 
+export type GraphQLFieldExecutor = (
+  exeContext: ExecutionContext,
+  parentType: GraphQLObjectType,
+  source: unknown,
+  fieldNodes: ReadonlyArray<FieldNode>,
+  path: Path,
+) => PromiseOrValue<unknown>;
+
 /**
  * The result of GraphQL execution.
  *
@@ -139,6 +148,7 @@ export interface ExecutionArgs {
   operationName?: Maybe<string>;
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
   typeResolver?: Maybe<GraphQLTypeResolver<any, any>>;
+  fieldExecutor?: Maybe<GraphQLFieldExecutor>;
 }
 
 /**
@@ -161,6 +171,7 @@ export function execute(args: ExecutionArgs): PromiseOrValue<ExecutionResult> {
     operationName,
     fieldResolver,
     typeResolver,
+    fieldExecutor,
   } = args;
 
   // If arguments are missing or incorrect, throw an error.
@@ -177,6 +188,7 @@ export function execute(args: ExecutionArgs): PromiseOrValue<ExecutionResult> {
     operationName,
     fieldResolver,
     typeResolver,
+    fieldExecutor,
   );
 
   // Return early errors if execution context failed.
@@ -267,6 +279,7 @@ export function buildExecutionContext(
   operationName: Maybe<string>,
   fieldResolver: Maybe<GraphQLFieldResolver<unknown, unknown>>,
   typeResolver?: Maybe<GraphQLTypeResolver<unknown, unknown>>,
+  fieldExecutor?: Maybe<GraphQLFieldExecutor>,
 ): ReadonlyArray<GraphQLError> | ExecutionContext {
   let operation: OperationDefinitionNode | undefined;
   const fragments: ObjMap<FragmentDefinitionNode> = Object.create(null);
@@ -322,6 +335,7 @@ export function buildExecutionContext(
     variableValues: coercedVariableValues.coerced,
     fieldResolver: fieldResolver ?? defaultFieldResolver,
     typeResolver: typeResolver ?? defaultTypeResolver,
+    fieldExecutor: fieldExecutor ?? defaultFieldExecutor,
     errors: [],
   };
 }
@@ -381,7 +395,7 @@ function executeFieldsSerially(
     fields.entries(),
     (results, [responseName, fieldNodes]) => {
       const fieldPath = addPath(path, responseName, parentType.name);
-      const result = executeField(
+      const result = exeContext.fieldExecutor(
         exeContext,
         parentType,
         sourceValue,
@@ -420,7 +434,7 @@ function executeFields(
 
   for (const [responseName, fieldNodes] of fields.entries()) {
     const fieldPath = addPath(path, responseName, parentType.name);
-    const result = executeField(
+    const result = exeContext.fieldExecutor(
       exeContext,
       parentType,
       sourceValue,
@@ -588,13 +602,13 @@ function getFieldEntryKey(node: FieldNode): string {
  * calling its resolve function, then calls completeValue to complete promises,
  * serialize scalars, or execute the sub-selection-set for objects.
  */
-function executeField(
-  exeContext: ExecutionContext,
-  parentType: GraphQLObjectType,
-  source: unknown,
-  fieldNodes: ReadonlyArray<FieldNode>,
-  path: Path,
-): PromiseOrValue<unknown> {
+export const defaultFieldExecutor: GraphQLFieldExecutor = (
+  exeContext,
+  parentType,
+  source,
+  fieldNodes,
+  path,
+) => {
   const fieldDef = getFieldDef(exeContext.schema, parentType, fieldNodes[0]);
   if (!fieldDef) {
     return;
@@ -658,7 +672,7 @@ function executeField(
     const error = locatedError(rawError, fieldNodes, pathToArray(path));
     return handleFieldError(error, returnType, exeContext);
   }
-}
+};
 
 /**
  * @internal

src/execution/index.ts

@@ -3,14 +3,17 @@ export { pathToArray as responsePathAsArray } from '../jsutils/Path';
 export {
   execute,
   executeSync,
+  defaultFieldExecutor,
   defaultFieldResolver,
   defaultTypeResolver,
 } from './execute';
 
 export type {
   ExecutionArgs,
+  ExecutionContext,
   ExecutionResult,
   FormattedExecutionResult,
+  GraphQLFieldExecutor,
 } from './execute';
 
 export { getDirectiveValues } from './values';

src/graphql.ts

@@ -14,7 +14,10 @@ import type {
 import type { GraphQLSchema } from './type/schema';
 import { validateSchema } from './type/validate';
 
-import type { ExecutionResult } from './execution/execute';
+import type {
+  ExecutionResult,
+  GraphQLFieldExecutor,
+} from './execution/execute';
 import { execute } from './execution/execute';
 
 /**
@@ -55,6 +58,11 @@ import { execute } from './execution/execute';
  *    A type resolver function to use when none is provided by the schema.
  *    If not provided, the default type resolver is used (which looks for a
  *    `__typename` field or alternatively calls the `isTypeOf` method).
+ * fieldExecutor:
+ *    An executor function to use when one is not provided by the schema.
+ *    If not provided, the default field executor is used (which properly
+ *    calls the field resolver and completes values according to the
+ *    GraphQL spec).
  */
 export interface GraphQLArgs {
   schema: GraphQLSchema;
@@ -65,6 +73,7 @@ export interface GraphQLArgs {
   operationName?: Maybe<string>;
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
   typeResolver?: Maybe<GraphQLTypeResolver<any, any>>;
+  fieldExecutor?: Maybe<GraphQLFieldExecutor>;
 }
 
 export function graphql(args: GraphQLArgs): Promise<ExecutionResult> {
@@ -99,6 +108,7 @@ function graphqlImpl(args: GraphQLArgs): PromiseOrValue<ExecutionResult> {
     operationName,
     fieldResolver,
     typeResolver,
+    fieldExecutor,
   } = args;
 
   // Validate Schema
@@ -131,5 +141,6 @@ function graphqlImpl(args: GraphQLArgs): PromiseOrValue<ExecutionResult> {
     operationName,
     fieldResolver,
     typeResolver,
+    fieldExecutor,
   });
 }

src/index.ts

@@ -301,6 +301,7 @@ export type {
 export {
   execute,
   executeSync,
+  defaultFieldExecutor,
   defaultFieldResolver,
   defaultTypeResolver,
   responsePathAsArray,
@@ -309,8 +310,10 @@ export {
 
 export type {
   ExecutionArgs,
+  ExecutionContext,
   ExecutionResult,
   FormattedExecutionResult,
+  GraphQLFieldExecutor,
 } from './execution/index';
 
 export { subscribe, createSourceEventStream } from './subscription/index';

src/subscription/subscribe.ts

@@ -8,7 +8,11 @@ import { locatedError } from '../error/locatedError';
 
 import type { DocumentNode } from '../language/ast';
 
-import type { ExecutionResult, ExecutionContext } from '../execution/execute';
+import type {
+  ExecutionResult,
+  ExecutionContext,
+  GraphQLFieldExecutor,
+} from '../execution/execute';
 import { getArgumentValues } from '../execution/values';
 import {
   assertValidExecutionArguments,
@@ -34,6 +38,7 @@ export interface SubscriptionArgs {
   variableValues?: Maybe<{ readonly [variable: string]: unknown }>;
   operationName?: Maybe<string>;
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
+  fieldExecutor?: Maybe<GraphQLFieldExecutor>;
   subscribeFieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
 }
 
@@ -69,6 +74,7 @@ export async function subscribe(
     variableValues,
     operationName,
     fieldResolver,
+    fieldExecutor,
     subscribeFieldResolver,
   } = args;
 
@@ -101,6 +107,7 @@ export async function subscribe(
       variableValues,
       operationName,
       fieldResolver,
+      fieldExecutor,
     });
 
   // Map every source value to a ExecutionResult value as described above.

src/validation/rules/SingleFieldSubscriptionsRule.ts

@@ -9,11 +9,14 @@ import type {
 import { Kind } from '../../language/kinds';
 
 import type { ValidationContext } from '../ValidationContext';
+
 import type { ExecutionContext } from '../../execution/execute';
+
 import {
   collectFields,
   defaultFieldResolver,
   defaultTypeResolver,
+  defaultFieldExecutor,
 } from '../../execution/execute';
 
 /**
@@ -52,6 +55,7 @@ export function SingleFieldSubscriptionsRule(
             variableValues,
             fieldResolver: defaultFieldResolver,
             typeResolver: defaultTypeResolver,
+            fieldExecutor: defaultFieldExecutor,
             errors: [],
           };
           const fields = collectFields(