util: Change how Error objects are formatted

Previously, Error objects were formatted as the result of a `toString`
call bounded by square brackets. They are now formatted as the stack
trace for the given error object. The intention initially was to emulate
how browsers do `console.error` but since that would also impact
`console.warn`, `console.log`, etc, it was decided to make the change at
`util.inspect` level which is in turn used by the `console` package.

Fixes: nodejs#4452
PR-URL: https://github.com/nodejs/node/pull/4582
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/util.js

@@ -488,7 +488,7 @@ function formatPrimitiveNoColor(ctx, value) {
 
 
 function formatError(value) {
-  return '[' + Error.prototype.toString.call(value) + ']';
+  return value.stack || '[' + Error.prototype.toString.call(value) + ']';
 }
 
 

test/parallel/test-util-format.js

@@ -1,8 +1,8 @@
 'use strict';
 require('../common');
-var assert = require('assert');
-var util = require('util');
-var symbol = Symbol('foo');
+const assert = require('assert');
+const util = require('util');
+const symbol = Symbol('foo');
 
 assert.equal(util.format(), '');
 assert.equal(util.format(''), '');
@@ -55,13 +55,26 @@ assert.equal(util.format('%%%s%%%%', 'hi'), '%hi%%');
 })();
 
 // Errors
-assert.equal(util.format(new Error('foo')), '[Error: foo]');
+const err = new Error('foo');
+assert.equal(util.format(err), err.stack);
 function CustomError(msg) {
   Error.call(this);
   Object.defineProperty(this, 'message',
                         { value: msg, enumerable: false });
   Object.defineProperty(this, 'name',
                         { value: 'CustomError', enumerable: false });
+  Error.captureStackTrace(this, CustomError);
 }
 util.inherits(CustomError, Error);
-assert.equal(util.format(new CustomError('bar')), '[CustomError: bar]');
+const customError = new CustomError('bar');
+assert.equal(util.format(customError), customError.stack);
+// Doesn't capture stack trace
+function BadCustomError(msg) {
+  Error.call(this);
+  Object.defineProperty(this, 'message',
+                        { value: msg, enumerable: false });
+  Object.defineProperty(this, 'name',
+                        { value: 'BadCustomError', enumerable: false });
+}
+util.inherits(BadCustomError, Error);
+assert.equal(util.format(new BadCustomError('foo')), '[BadCustomError: foo]');

test/parallel/test-util-inspect.js

@@ -1,7 +1,7 @@
 'use strict';
 require('../common');
-var assert = require('assert');
-var util = require('util');
+const assert = require('assert');
+const util = require('util');
 const vm = require('vm');
 
 assert.equal(util.inspect(1), '1');
@@ -288,19 +288,33 @@ assert.equal(util.inspect(setter, true), '{ [b]: [Setter] }');
 assert.equal(util.inspect(getterAndSetter, true), '{ [c]: [Getter/Setter] }');
 
 // exceptions should print the error message, not '{}'
-assert.equal(util.inspect(new Error()), '[Error]');
-assert.equal(util.inspect(new Error('FAIL')), '[Error: FAIL]');
-assert.equal(util.inspect(new TypeError('FAIL')), '[TypeError: FAIL]');
-assert.equal(util.inspect(new SyntaxError('FAIL')), '[SyntaxError: FAIL]');
+const errors = [];
+errors.push(new Error());
+errors.push(new Error('FAIL'));
+errors.push(new TypeError('FAIL'));
+errors.push(new SyntaxError('FAIL'));
+errors.forEach(function(err) {
+  assert.equal(util.inspect(err), err.stack);
+});
 try {
   undef();
 } catch (e) {
-  assert.equal(util.inspect(e), '[ReferenceError: undef is not defined]');
+  assert.equal(util.inspect(e), e.stack);
 }
 var ex = util.inspect(new Error('FAIL'), true);
-assert.ok(ex.indexOf('[Error: FAIL]') != -1);
+assert.ok(ex.indexOf('Error: FAIL') != -1);
 assert.ok(ex.indexOf('[stack]') != -1);
 assert.ok(ex.indexOf('[message]') != -1);
+// Doesn't capture stack trace
+function BadCustomError(msg) {
+  Error.call(this);
+  Object.defineProperty(this, 'message',
+                        { value: msg, enumerable: false });
+  Object.defineProperty(this, 'name',
+                        { value: 'BadCustomError', enumerable: false });
+}
+util.inherits(BadCustomError, Error);
+assert.equal(util.inspect(new BadCustomError('foo')), '[BadCustomError: foo]');
 
 // GH-1941
 // should not throw: