console: add color support

Add a way to tell `Console` instances to either always use, never use
or auto-detect color support and inspect objects accordingly.

PR-URL: https://github.com/nodejs/node/pull/19372
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/console.md

@@ -87,7 +87,8 @@ changes:
     description: The `ignoreErrors` option was introduced.
   - version: REPLACEME
     pr-url: https://github.com/nodejs/node/pull/19372
-    description: The `Console` constructor now supports an `options` argument.
+    description: The `Console` constructor now supports an `options` argument,
+                 and the `colorMode` option was introduced.
 -->
 
 * `options` {Object}
@@ -95,6 +96,11 @@ changes:
   * `stderr` {stream.Writable}
   * `ignoreErrors` {boolean} Ignore errors when writing to the underlying
                              streams. **Default:** `true`.
+  * `colorMode` {boolean|string} Set color support for this `Console` instance.
+    Setting to `true` enables coloring while inspecting values, setting to
+    `'auto'` will make color support depend on the value of the `isTTY` property
+    and the value returned by `getColorDepth()` on the respective stream.
+    **Default:** `false`
 
 Creates a new `Console` with one or two writable stream instances. `stdout` is a
 writable stream to print log or info output. `stderr` is used for warning or

doc/api/util.md

@@ -268,8 +268,8 @@ an `inspectOptions` argument which specifies options that are passed along to
 
 ```js
 util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });
-  // Returns 'See object { foo: 42 }', where `42` is colored as a number
+// Returns 'See object { foo: 42 }', where `42` is colored as a number
-  // when printed to a terminal.
+// when printed to a terminal.
 ```
 
 ## util.getSystemErrorName(err)

lib/console.js

@@ -26,6 +26,7 @@ const {
   codes: {
     ERR_CONSOLE_WRITABLE_STREAM,
     ERR_INVALID_ARG_TYPE,
+    ERR_INVALID_ARG_VALUE,
   },
 } = require('internal/errors');
 const { previewMapIterator, previewSetIterator } = require('internal/v8');
@@ -49,24 +50,32 @@ const {
 } = Array;
 
 // Track amount of indentation required via `console.group()`.
-const kGroupIndent = Symbol('groupIndent');
+const kGroupIndent = Symbol('kGroupIndent');
+
+const kFormatForStderr = Symbol('kFormatForStderr');
+const kFormatForStdout = Symbol('kFormatForStdout');
+const kGetInspectOptions = Symbol('kGetInspectOptions');
+const kColorMode = Symbol('kColorMode');
 
 function Console(options /* or: stdout, stderr, ignoreErrors = true */) {
   if (!(this instanceof Console)) {
     return new Console(...arguments);
   }
 
-  let stdout, stderr, ignoreErrors;
+  let stdout, stderr, ignoreErrors, colorMode;
   if (options && typeof options.write !== 'function') {
     ({
       stdout,
       stderr = stdout,
-      ignoreErrors = true
+      ignoreErrors = true,
+      colorMode = false
     } = options);
   } else {
-    stdout = options;
+    return new Console({
-    stderr = arguments[1];
+      stdout: options,
-    ignoreErrors = arguments[2] === undefined ? true : arguments[2];
+      stderr: arguments[1],
+      ignoreErrors: arguments[2]
+    });
   }
 
   if (!stdout || typeof stdout.write !== 'function') {
@@ -94,7 +103,11 @@ function Console(options /* or: stdout, stderr, ignoreErrors = true */) {
   prop.value = createWriteErrorHandler(stderr);
   Object.defineProperty(this, '_stderrErrorHandler', prop);
 
+  if (typeof colorMode !== 'boolean' && colorMode !== 'auto')
+    throw new ERR_INVALID_ARG_VALUE('colorMode', colorMode);
+
   this[kCounts] = new Map();
+  this[kColorMode] = colorMode;
 
   Object.defineProperty(this, kGroupIndent, { writable: true });
   this[kGroupIndent] = '';
@@ -156,13 +169,33 @@ function write(ignoreErrors, stream, string, errorhandler, groupIndent) {
   }
 }
 
+const kColorInspectOptions = { colors: true };
+const kNoColorInspectOptions = {};
+Console.prototype[kGetInspectOptions] = function(stream) {
+  let color = this[kColorMode];
+  if (color === 'auto') {
+    color = stream.isTTY && (
+      typeof stream.getColorDepth === 'function' ?
+        stream.getColorDepth() > 2 : true);
+  }
+
+  return color ? kColorInspectOptions : kNoColorInspectOptions;
+};
+
+Console.prototype[kFormatForStdout] = function(args) {
+  const opts = this[kGetInspectOptions](this._stdout);
+  return util.formatWithOptions(opts, ...args);
+};
+
+Console.prototype[kFormatForStderr] = function(args) {
+  const opts = this[kGetInspectOptions](this._stderr);
+  return util.formatWithOptions(opts, ...args);
+};
+
 Console.prototype.log = function log(...args) {
   write(this._ignoreErrors,
         this._stdout,
-        // The performance of .apply and the spread operator seems on par in V8
+        this[kFormatForStdout](args),
-        // 6.3 but the spread operator, unlike .apply(), pushes the elements
-        // onto the stack. That is, it makes stack overflows more likely.
-        util.format.apply(null, args),
         this._stdoutErrorHandler,
         this[kGroupIndent]);
 };
@@ -173,14 +206,16 @@ Console.prototype.dirxml = Console.prototype.log;
 Console.prototype.warn = function warn(...args) {
   write(this._ignoreErrors,
         this._stderr,
-        util.format.apply(null, args),
+        this[kFormatForStderr](args),
         this._stderrErrorHandler,
         this[kGroupIndent]);
 };
 Console.prototype.error = Console.prototype.warn;
 
 Console.prototype.dir = function dir(object, options) {
-  options = Object.assign({ customInspect: false }, options);
+  options = Object.assign({
+    customInspect: false
+  }, this[kGetInspectOptions](this._stdout), options);
   write(this._ignoreErrors,
         this._stdout,
         util.inspect(object, options),
@@ -211,7 +246,7 @@ Console.prototype.timeEnd = function timeEnd(label = 'default') {
 Console.prototype.trace = function trace(...args) {
   const err = {
     name: 'Trace',
-    message: util.format.apply(null, args)
+    message: this[kFormatForStderr](args)
   };
   Error.captureStackTrace(err, trace);
   this.error(err.stack);
@@ -220,7 +255,7 @@ Console.prototype.trace = function trace(...args) {
 Console.prototype.assert = function assert(expression, ...args) {
   if (!expression) {
     args[0] = `Assertion failed${args.length === 0 ? '' : `: ${args[0]}`}`;
-    this.warn(util.format.apply(null, args));
+    this.warn(this[kFormatForStderr](args));
   }
 };
 

test/parallel/test-console-tty-colors.js

@@ -0,0 +1,46 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const util = require('util');
+const { Writable } = require('stream');
+const { Console } = require('console');
+
+function check(isTTY, colorMode, expectedColorMode) {
+  const items = [
+    1,
+    { a: 2 },
+    [ 'foo' ],
+    { '\\a': '\\bar' }
+  ];
+
+  let i = 0;
+  const stream = new Writable({
+    write: common.mustCall((chunk, enc, cb) => {
+      assert.strictEqual(chunk.trim(),
+                         util.inspect(items[i++], {
+                           colors: expectedColorMode
+                         }));
+      cb();
+    }, items.length),
+    decodeStrings: false
+  });
+  stream.isTTY = isTTY;
+
+  // Set ignoreErrors to `false` here so that we see assertion failures
+  // from the `write()` call happen.
+  const testConsole = new Console({
+    stdout: stream,
+    ignoreErrors: false,
+    colorMode
+  });
+  for (const item of items) {
+    testConsole.log(item);
+  }
+}
+
+check(true, 'auto', true);
+check(false, 'auto', false);
+check(true, true, true);
+check(false, true, true);
+check(true, false, false);
+check(false, false, false);

test/parallel/test-console.js

@@ -51,9 +51,11 @@ const custom_inspect = { foo: 'bar', inspect: () => 'inspect' };
 
 const strings = [];
 const errStrings = [];
+process.stdout.isTTY = false;
 common.hijackStdout(function(data) {
   strings.push(data);
 });
+process.stderr.isTTY = false;
 common.hijackStderr(function(data) {
   errStrings.push(data);
 });