Correctly handle custom inspect fn that returns object value

src/jsutils/__tests__/inspect-test.js

@@ -78,7 +78,7 @@ describe('inspect', () => {
     expect(inspect(object)).to.equal('<custom inspect>');
   });
 
-  it('custom inspect', () => {
+  it('custom symbol inspect is take precedence', () => {
     invariant(nodejsCustomInspectSymbol);
 
     const object = {
@@ -92,4 +92,25 @@ describe('inspect', () => {
 
     expect(inspect(object)).to.equal('<custom symbol inspect>');
   });
+
+  it('custom inspect returning object values', () => {
+    const object = {
+      inspect() {
+        return { custom: 'inspect' };
+      },
+    };
+
+    expect(inspect(object)).to.equal('{ custom: "inspect" }');
+  });
+
+  it('custom inspect function that uses this', () => {
+    const object = {
+      str: 'Hello World!',
+      inspect() {
+        return this.str;
+      },
+    };
+
+    expect(inspect(object)).to.equal('Hello World!');
+  });
 });

src/jsutils/inspect.js

@@ -20,11 +20,13 @@ export default function inspect(value: mixed): string {
       return value.name ? `[function ${value.name}]` : '[function]';
     case 'object':
       if (value) {
-        const customInspectFn = value[String(nodejsCustomInspectSymbol)];
-        if (typeof customInspectFn === 'function') {
-          return customInspectFn();
-        } else if (typeof value.inspect === 'function') {
-          return value.inspect();
+        const customInspectFn = getCustomFn(value);
+
+        if (customInspectFn) {
+          const customValue = customInspectFn.call(value);
+          return typeof customValue === 'string'
+            ? customValue
+            : inspect(customValue);
         } else if (Array.isArray(value)) {
           return '[' + value.map(inspect).join(', ') + ']';
         }
@@ -39,3 +41,15 @@ export default function inspect(value: mixed): string {
       return String(value);
   }
 }
+
+function getCustomFn(object) {
+  const customInspectFn = object[String(nodejsCustomInspectSymbol)];
+
+  if (typeof customInspectFn === 'function') {
+    return customInspectFn;
+  }
+
+  if (typeof object.inspect === 'function') {
+    return object.inspect;
+  }
+}

src/language/__tests__/lexer-test.js

@@ -7,11 +7,12 @@
  * @flow strict
  */
 
-import { inspect as utilInspect } from 'util';
+import { inspect as nodeInspect } from 'util';
 
 import { expect } from 'chai';
 import { describe, it } from 'mocha';
 import dedent from '../../jsutils/dedent';
+import inspect from '../../jsutils/inspect';
 import { GraphQLError } from '../../error';
 import { Source } from '../source';
 import { createLexer, TokenKind } from '../lexer';
@@ -62,14 +63,17 @@ describe('Lexer', () => {
     });
   });
 
-  it('can be JSON.stringified or util.inspected', () => {
+  it('can be JSON.stringified, util.inspected or jsutils.inspect', () => {
     const token = lexOne('foo');
     expect(JSON.stringify(token)).to.equal(
       '{"kind":"Name","value":"foo","line":1,"column":1}',
     );
-    expect(utilInspect(token)).to.equal(
+    expect(nodeInspect(token)).to.equal(
       "{ kind: 'Name', value: 'foo', line: 1, column: 1 }",
     );
+    expect(inspect(token)).to.equal(
+      '{ kind: "Name", value: "foo", line: 1, column: 1 }',
+    );
   });
 
   it('skips whitespace and comments', () => {

src/language/__tests__/parser-test.js

@@ -7,7 +7,7 @@
  * @flow strict
  */
 
-import { inspect } from 'util';
+import { inspect as nodeInspect } from 'util';
 import { readFileSync } from 'fs';
 import { join } from 'path';
 
@@ -18,6 +18,7 @@ import { TokenKind } from '../lexer';
 import { parse, parseValue, parseType } from '../parser';
 import { Source } from '../source';
 import dedent from '../../jsutils/dedent';
+import inspect from '../../jsutils/inspect';
 import toJSONDeep from './toJSONDeep';
 
 function expectSyntaxError(text, message, location) {
@@ -391,6 +392,7 @@ describe('Parser', () => {
     const result = parse('{ id }');
 
     expect(JSON.stringify(result.loc)).to.equal('{"start":0,"end":6}');
+    expect(nodeInspect(result.loc)).to.equal('{ start: 0, end: 6 }');
     expect(inspect(result.loc)).to.equal('{ start: 0, end: 6 }');
   });