util: improve function inspection

This commit contains the following changes:

1) Add null prototype support for functions.
2) Safely detect async and generator functions.
3) Mark anonymous functions as such instead of just leaving out the
   name.

PR-URL: https://github.com/nodejs/node/pull/27227
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/internal/util/inspect.js

@@ -49,6 +49,8 @@ const {
 } = require('internal/errors');
 
 const {
+  isAsyncFunction,
+  isGeneratorFunction,
   isAnyArrayBuffer,
   isArrayBuffer,
   isArgumentsObject,
@@ -642,14 +644,9 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
         return `${braces[0]}}`;
       }
     } else if (typeof value === 'function') {
-      const type = constructor || tag || 'Function';
+      base = getFunctionBase(value, constructor, tag);
-      let name = `${type}`;
-      if (value.name && typeof value.name === 'string') {
-        name += `: ${value.name}`;
-      }
       if (keys.length === 0)
-        return ctx.stylize(`[${name}]`, 'special');
+        return ctx.stylize(base, 'special');
-      base = `[${name}]`;
     } else if (isRegExp(value)) {
       // Make RegExps say that they are RegExps
       base = RegExpPrototype.toString(
@@ -834,6 +831,32 @@ function getBoxedBase(value, ctx, keys, constructor, tag) {
   return ctx.stylize(base, type.toLowerCase());
 }
 
+function getFunctionBase(value, constructor, tag) {
+  let type = 'Function';
+  if (isAsyncFunction(value)) {
+    type = 'AsyncFunction';
+  } else if (isGeneratorFunction(value)) {
+    type = 'GeneratorFunction';
+  }
+  let base = `[${type}`;
+  if (constructor === null) {
+    base += ' (null prototype)';
+  }
+  if (value.name === '') {
+    base += ' (anonymous)';
+  } else {
+    base += `: ${value.name}`;
+  }
+  base += ']';
+  if (constructor !== type && constructor !== null) {
+    base += ` ${constructor}`;
+  }
+  if (tag !== '' && constructor !== tag) {
+    base += ` [${tag}]`;
+  }
+  return base;
+}
+
 function formatError(err, constructor, tag, ctx) {
   // TODO(BridgeAR): Always show the error code if present.
   let stack = err.stack || ErrorPrototype.toString(err);

test/parallel/test-assert.js

@@ -289,7 +289,7 @@ testAssertionMessage(undefined, 'undefined');
 testAssertionMessage(-Infinity, '-Infinity');
 testAssertionMessage([1, 2, 3], '[\n+   1,\n+   2,\n+   3\n+ ]');
 testAssertionMessage(function f() {}, '[Function: f]');
-testAssertionMessage(function() {}, '[Function]');
+testAssertionMessage(function() {}, '[Function (anonymous)]');
 testAssertionMessage(circular, '{\n+   x: [Circular],\n+   y: 1\n+ }');
 testAssertionMessage({ a: undefined, b: null },
                      '{\n+   a: undefined,\n+   b: null\n+ }');
@@ -597,7 +597,7 @@ assert.throws(
     '\n' +
     '+ {}\n' +
     '- {\n' +
-    '-   [Symbol(nodejs.util.inspect.custom)]: [Function],\n' +
+    '-   [Symbol(nodejs.util.inspect.custom)]: [Function (anonymous)],\n' +
     "-   loop: 'forever'\n" +
     '- }'
   });

test/parallel/test-console-table.js

@@ -32,7 +32,7 @@ test(undefined, 'undefined\n');
 test(false, 'false\n');
 test('hi', 'hi\n');
 test(Symbol(), 'Symbol()\n');
-test(function() {}, '[Function]\n');
+test(function() {}, '[Function (anonymous)]\n');
 
 test([1, 2, 3], `
 ┌─────────┬────────┐

test/parallel/test-repl.js

@@ -308,7 +308,7 @@ const errorTests = [
   // Functions should not evaluate twice (#2773)
   {
     send: 'var I = [1,2,3,function() {}]; I.pop()',
-    expect: '[Function]'
+    expect: '[Function (anonymous)]'
   },
   // Multiline object
   {

test/parallel/test-util-format.js

@@ -288,7 +288,7 @@ assert.strictEqual(util.format('abc%', 1), 'abc% 1');
 
 // Additional arguments after format specifiers
 assert.strictEqual(util.format('%i', 1, 'number'), '1 number');
-assert.strictEqual(util.format('%i', 1, () => {}), '1 [Function]');
+assert.strictEqual(util.format('%i', 1, () => {}), '1 [Function (anonymous)]');
 
 {
   const o = {};
@@ -339,8 +339,8 @@ assert.strictEqual(util.format('1', '1'), '1 1');
 assert.strictEqual(util.format(1, '1'), '1 1');
 assert.strictEqual(util.format('1', 1), '1 1');
 assert.strictEqual(util.format(1, -0), '1 -0');
-assert.strictEqual(util.format('1', () => {}), '1 [Function]');
+assert.strictEqual(util.format('1', () => {}), '1 [Function (anonymous)]');
-assert.strictEqual(util.format(1, () => {}), '1 [Function]');
+assert.strictEqual(util.format(1, () => {}), '1 [Function (anonymous)]');
 assert.strictEqual(util.format('1', "'"), "1 '");
 assert.strictEqual(util.format(1, "'"), "1 '");
 assert.strictEqual(util.format('1', 'number'), '1 number');

test/parallel/test-util-inspect-proxy.js

@@ -144,7 +144,7 @@ const proxy11 = new Proxy(() => {}, {
     return proxy11;
   }
 });
-const expected10 = '[Function]';
+const expected10 = '[Function (anonymous)]';
-const expected11 = '[Function]';
+const expected11 = '[Function (anonymous)]';
 assert.strictEqual(util.inspect(proxy10), expected10);
 assert.strictEqual(util.inspect(proxy11), expected11);

test/parallel/test-util-inspect.js

@@ -33,11 +33,51 @@ assert.strictEqual(util.inspect(1), '1');
 assert.strictEqual(util.inspect(false), 'false');
 assert.strictEqual(util.inspect(''), "''");
 assert.strictEqual(util.inspect('hello'), "'hello'");
-assert.strictEqual(util.inspect(function() {}), '[Function]');
+assert.strictEqual(util.inspect(function abc() {}), '[Function: abc]');
-assert.strictEqual(util.inspect(() => {}), '[Function]');
+assert.strictEqual(util.inspect(() => {}), '[Function (anonymous)]');
-assert.strictEqual(util.inspect(async function() {}), '[AsyncFunction]');
+assert.strictEqual(
-assert.strictEqual(util.inspect(async () => {}), '[AsyncFunction]');
+  util.inspect(async function() {}),
-assert.strictEqual(util.inspect(function*() {}), '[GeneratorFunction]');
+  '[AsyncFunction (anonymous)]'
+);
+assert.strictEqual(util.inspect(async () => {}), '[AsyncFunction (anonymous)]');
+
+// Special function inspection.
+{
+  const fn = (() => function*() {})();
+  assert.strictEqual(
+    util.inspect(fn),
+    '[GeneratorFunction (anonymous)]'
+  );
+  Object.setPrototypeOf(fn, Object.getPrototypeOf(async () => {}));
+  assert.strictEqual(
+    util.inspect(fn),
+    '[GeneratorFunction (anonymous)] AsyncFunction'
+  );
+  Object.defineProperty(fn, 'name', { value: 5, configurable: true });
+  assert.strictEqual(
+    util.inspect(fn),
+    '[GeneratorFunction: 5] AsyncFunction'
+  );
+  Object.defineProperty(fn, Symbol.toStringTag, {
+    value: 'Foobar',
+    configurable: true
+  });
+  assert.strictEqual(
+    util.inspect({ ['5']: fn }),
+    "{ '5': [GeneratorFunction: 5] AsyncFunction [Foobar] }"
+  );
+  Object.defineProperty(fn, 'name', { value: '5', configurable: true });
+  Object.setPrototypeOf(fn, null);
+  assert.strictEqual(
+    util.inspect(fn),
+    '[GeneratorFunction (null prototype): 5] [Foobar]'
+  );
+  assert.strictEqual(
+    util.inspect({ ['5']: fn }),
+    "{ '5': [GeneratorFunction (null prototype): 5] [Foobar] }"
+  );
+}
+
 assert.strictEqual(util.inspect(undefined), 'undefined');
 assert.strictEqual(util.inspect(null), 'null');
 assert.strictEqual(util.inspect(/foo(bar\n)?/gi), '/foo(bar\\n)?/gi');
@@ -59,8 +99,9 @@ assert.strictEqual(util.inspect({}), '{}');
 assert.strictEqual(util.inspect({ a: 1 }), '{ a: 1 }');
 assert.strictEqual(util.inspect({ a: function() {} }), '{ a: [Function: a] }');
 assert.strictEqual(util.inspect({ a: () => {} }), '{ a: [Function: a] }');
-assert.strictEqual(util.inspect({ a: async function() {} }),
+// eslint-disable-next-line func-name-matching
-                   '{ a: [AsyncFunction: a] }');
+assert.strictEqual(util.inspect({ a: async function abc() {} }),
+                   '{ a: [AsyncFunction: abc] }');
 assert.strictEqual(util.inspect({ a: async () => {} }),
                    '{ a: [AsyncFunction: a] }');
 assert.strictEqual(util.inspect({ a: function*() {} }),
@@ -411,7 +452,10 @@ assert.strictEqual(
 {
   const value = (() => function() {})();
   value.aprop = 42;
-  assert.strictEqual(util.inspect(value), '[Function] { aprop: 42 }');
+  assert.strictEqual(
+    util.inspect(value),
+    '[Function (anonymous)] { aprop: 42 }'
+  );
 }
 
 // Regular expressions with properties.
@@ -1441,7 +1485,7 @@ util.inspect(process);
   out = util.inspect(o, { compact: false, breakLength: 3 });
   expect = [
     '{',
-    '  a: [Function],',
+    '  a: [Function (anonymous)],',
     '  b: [Number: 3]',
     '}'
   ].join('\n');
@@ -1450,7 +1494,7 @@ util.inspect(process);
   out = util.inspect(o, { compact: false, breakLength: 3, showHidden: true });
   expect = [
     '{',
-    '  a: [Function] {',
+    '  a: [Function (anonymous)] {',
     '    [length]: 0,',
     "    [name]: ''",
     '  },',
@@ -1767,8 +1811,8 @@ assert.strictEqual(util.inspect('"\'${a}'), "'\"\\'${a}'");
   [new Number(55), '[Number: 55]'],
   [Object(BigInt(55)), '[BigInt: 55n]'],
   [Object(Symbol('foo')), '[Symbol: Symbol(foo)]'],
-  [function() {}, '[Function]'],
+  [function() {}, '[Function (anonymous)]'],
-  [() => {}, '[Function]'],
+  [() => {}, '[Function (anonymous)]'],
   [[1, 2], '[ 1, 2 ]'],
   [[, , 5, , , , ], '[ <2 empty items>, 5, <3 empty items> ]'],
   [{ a: 5 }, '{ a: 5 }'],
@@ -1957,10 +2001,14 @@ assert.strictEqual(
   let value = (function() { return function() {}; })();
   Object.setPrototypeOf(value, null);
   Object.setPrototypeOf(obj, value);
-  assert.strictEqual(util.inspect(obj), '<[Function]> { a: true }');
+  assert.strictEqual(
+    util.inspect(obj),
+    '<[Function (null prototype) (anonymous)]> { a: true }'
+  );
   assert.strictEqual(
     util.inspect(obj, { colors: true }),
-    '<\u001b[36m[Function]\u001b[39m> { a: \u001b[33mtrue\u001b[39m }'
+    '<\u001b[36m[Function (null prototype) (anonymous)]\u001b[39m> ' +
+      '{ a: \u001b[33mtrue\u001b[39m }'
   );
 
   obj = { a: true };