console: implement minimal `console.group()`

Node.js exposes `console.group()` and `console.groupEnd()` via the
inspector. These functions have no apparent effect when called from
Node.js without the inspector. We cannot easily hide them when Node.js
is started without the inspector because we support opening the
inspector during runtime via `inspector.port()`.

Implement a minimal `console.group()`/`console.groupEnd()`. More
sophisticated implementations are possible, but they can be done in
userland and/or features can be added to this at a later time.

`console.groupCollapsed()` is implemented as an alias for
`console.group()`.

PR-URL: https://github.com/nodejs/node/pull/14910
Fixes: https://github.com/nodejs/node/issues/1716
Ref: https://github.com/nodejs/node/issues/12675
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/console.md

@@ -286,6 +286,32 @@ If formatting elements (e.g. `%d`) are not found in the first string then
 [`util.inspect()`][] is called on each argument and the resulting string
 values are concatenated. See [`util.format()`][] for more information.
 
+### console.group([...label])
+<!-- YAML
+added: REPLACEME
+-->
+
+* `label` {any}
+
+Increases indentation of subsequent lines by two spaces.
+
+If one or more `label`s are provided, those are printed first without the
+additional indentation.
+
+### console.groupCollapsed()
+<!-- YAML
+  added: REPLACEME
+-->
+
+An alias for [`console.group()`][].
+
+### console.groupEnd()
+<!-- YAML
+added: REPLACEME
+-->
+
+Decreases indentation of subsequent lines by two spaces.
+
 ### console.info([data][, ...args])
 <!-- YAML
 added: v0.1.100
@@ -390,6 +416,7 @@ added: v0.1.100
 The `console.warn()` function is an alias for [`console.error()`][].
 
 [`console.error()`]: #console_console_error_data_args
+[`console.group()`]: #console_console_group_label
 [`console.log()`]: #console_console_log_data_args
 [`console.time()`]: #console_console_time_label
 [`console.timeEnd()`]: #console_console_timeend_label

lib/console.js

@@ -25,6 +25,9 @@ const errors = require('internal/errors');
 const util = require('util');
 const kCounts = Symbol('counts');
 
+// Track amount of indentation required via `console.group()`.
+const kGroupIndent = Symbol('groupIndent');
+
 function Console(stdout, stderr, ignoreErrors = true) {
   if (!(this instanceof Console)) {
     return new Console(stdout, stderr, ignoreErrors);
@@ -57,6 +60,7 @@ function Console(stdout, stderr, ignoreErrors = true) {
   Object.defineProperty(this, '_stderrErrorHandler', prop);
 
   this[kCounts] = new Map();
+  this[kGroupIndent] = '';
 
   // bind the prototype functions to this Console instance
   var keys = Object.keys(Console.prototype);
@@ -111,7 +115,7 @@ function write(ignoreErrors, stream, string, errorhandler) {
 Console.prototype.log = function log(...args) {
   write(this._ignoreErrors,
         this._stdout,
-        `${util.format.apply(null, args)}\n`,
+        `${this[kGroupIndent]}${util.format.apply(null, args)}\n`,
         this._stdoutErrorHandler);
 };
 
@@ -122,7 +126,7 @@ Console.prototype.info = Console.prototype.log;
 Console.prototype.warn = function warn(...args) {
   write(this._ignoreErrors,
         this._stderr,
-        `${util.format.apply(null, args)}\n`,
+        `${this[kGroupIndent]}${util.format.apply(null, args)}\n`,
         this._stderrErrorHandler);
 };
 
@@ -134,7 +138,7 @@ Console.prototype.dir = function dir(object, options) {
   options = Object.assign({ customInspect: false }, options);
   write(this._ignoreErrors,
         this._stdout,
-        `${util.inspect(object, options)}\n`,
+        `${this[kGroupIndent]}${util.inspect(object, options)}\n`,
         this._stdoutErrorHandler);
 };
 
@@ -214,6 +218,20 @@ Console.prototype.countReset = function countReset(label = 'default') {
   counts.delete(`${label}`);
 };
 
+Console.prototype.group = function group(...data) {
+  if (data.length > 0) {
+    this.log(...data);
+  }
+  this[kGroupIndent] += '  ';
+};
+
+Console.prototype.groupCollapsed = Console.prototype.group;
+
+Console.prototype.groupEnd = function groupEnd() {
+  this[kGroupIndent] =
+    this[kGroupIndent].slice(0, this[kGroupIndent].length - 2);
+};
+
 module.exports = new Console(process.stdout, process.stderr);
 module.exports.Console = Console;
 

test/parallel/test-console-group.js

@@ -0,0 +1,111 @@
+'use strict';
+const common = require('../common');
+
+const assert = require('assert');
+const Console = require('console').Console;
+
+let c, stdout, stderr;
+
+function setup() {
+  stdout = '';
+  common.hijackStdout(function(data) {
+    stdout += data;
+  });
+
+  stderr = '';
+  common.hijackStderr(function(data) {
+    stderr += data;
+  });
+
+  c = new Console(process.stdout, process.stderr);
+}
+
+function teardown() {
+  common.restoreStdout();
+  common.restoreStderr();
+}
+
+// Basic group() functionality
+{
+  setup();
+  const expectedOut = 'This is the outer level\n' +
+                      '  Level 2\n' +
+                      '    Level 3\n' +
+                      '  Back to level 2\n' +
+                      'Back to the outer level\n' +
+                      'Still at the outer level\n';
+
+
+  const expectedErr = '    More of level 3\n';
+
+  c.log('This is the outer level');
+  c.group();
+  c.log('Level 2');
+  c.group();
+  c.log('Level 3');
+  c.warn('More of level 3');
+  c.groupEnd();
+  c.log('Back to level 2');
+  c.groupEnd();
+  c.log('Back to the outer level');
+  c.groupEnd();
+  c.log('Still at the outer level');
+
+  assert.strictEqual(stdout, expectedOut);
+  assert.strictEqual(stderr, expectedErr);
+  teardown();
+}
+
+// Group indentation is tracked per Console instance.
+{
+  setup();
+  const expectedOut = 'No indentation\n' +
+                      'None here either\n' +
+                      '  Now the first console is indenting\n' +
+                      'But the second one does not\n';
+  const expectedErr = '';
+
+  const c2 = new Console(process.stdout, process.stderr);
+  c.log('No indentation');
+  c2.log('None here either');
+  c.group();
+  c.log('Now the first console is indenting');
+  c2.log('But the second one does not');
+
+  assert.strictEqual(stdout, expectedOut);
+  assert.strictEqual(stderr, expectedErr);
+  teardown();
+}
+
+// Make sure labels work.
+{
+  setup();
+  const expectedOut = 'This is a label\n' +
+                      '  And this is the data for that label\n';
+  const expectedErr = '';
+
+  c.group('This is a label');
+  c.log('And this is the data for that label');
+
+  assert.strictEqual(stdout, expectedOut);
+  assert.strictEqual(stderr, expectedErr);
+  teardown();
+}
+
+// Check that console.groupCollapsed() is an alias of console.group()
+{
+  setup();
+  const expectedOut = 'Label\n' +
+                      '  Level 2\n' +
+                      '    Level 3\n';
+  const expectedErr = '';
+
+  c.groupCollapsed('Label');
+  c.log('Level 2');
+  c.groupCollapsed();
+  c.log('Level 3');
+
+  assert.strictEqual(stdout, expectedOut);
+  assert.strictEqual(stderr, expectedErr);
+  teardown();
+}