tty: add getColorDepth function

Right now it is very difficult to determine if a terminal supports
colors or not. This function adds this functionality by detecting
environment variables and checking process.

PR-URL: https://github.com/nodejs/node/pull/17615
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/lib/tty.js b/lib/tty.js
index 2a62fcb859..dc3e2fcf82 100644
--- a/lib/tty.js
+++ b/lib/tty.js
@@ -28,6 +28,14 @@ const { inherits } = util;
 const errnoException = util._errnoException;
 const errors = require('internal/errors');
 const readline = require('readline');
+const { release } = require('os');
+
+const OSRelease = release().split('.');
+
+const COLORS_2 = 1;
+const COLORS_16 = 4;
+const COLORS_256 = 8;
+const COLORS_16m = 24;
 
 function isatty(fd) {
   return Number.isInteger(fd) && fd >= 0 && isTTY(fd);
@@ -104,6 +112,70 @@ inherits(WriteStream, net.Socket);
 
 WriteStream.prototype.isTTY = true;
 
+WriteStream.prototype.getColorDepth = function(env = process.env) {
+  if (env.NODE_DISABLE_COLORS || env.TERM === 'dumb' && !env.COLORTERM) {
+    return COLORS_2;
+  }
+
+  if (process.platform === 'win32') {
+    // Windows 10 build 10586 is the first Windows release that supports 256
+    // colors. Windows 10 build 14931 is the first release that supports
+    // 16m/TrueColor.
+    if (+OSRelease[0] >= 10) {
+      const build = +OSRelease[2];
+      if (build >= 14931)
+        return COLORS_16m;
+      if (build >= 10586)
+        return COLORS_256;
+    }
+
+    return COLORS_16;
+  }
+
+  if (env.TMUX) {
+    return COLORS_256;
+  }
+
+  if (env.CI) {
+    if ('TRAVIS' in env || 'CIRCLECI' in env || 'APPVEYOR' in env ||
+      'GITLAB_CI' in env || env.CI_NAME === 'codeship') {
+      return COLORS_256;
+    }
+    return COLORS_2;
+  }
+
+  if ('TEAMCITY_VERSION' in env) {
+    return /^(9\.(0*[1-9]\d*)\.|\d{2,}\.)/.test(env.TEAMCITY_VERSION) ?
+      COLORS_16 : COLORS_2;
+  }
+
+  switch (env.TERM_PROGRAM) {
+    case 'iTerm.app':
+      if (!env.TERM_PROGRAM_VERSION ||
+        /^[0-2]\./.test(env.TERM_PROGRAM_VERSION)) {
+        return COLORS_256;
+      }
+      return COLORS_16m;
+    case 'HyperTerm':
+    case 'Hyper':
+    case 'MacTerm':
+      return COLORS_16m;
+    case 'Apple_Terminal':
+      return COLORS_256;
+  }
+
+  if (env.TERM) {
+    if (/^xterm-256/.test(env.TERM))
+      return COLORS_256;
+    if (/^screen|^xterm|^vt100|color|ansi|cygwin|linux/i.test(env.TERM))
+      return COLORS_16;
+  }
+
+  if (env.COLORTERM)
+    return COLORS_16;
+
+  return COLORS_2;
+};
 
 WriteStream.prototype._refreshSize = function() {
   var oldCols = this.columns;