tty: add NO_COLOR and FORCE_COLOR support

This adds support to enforce a specific color depth by checking the
`FORCE_COLOR` environment variable similar to `chalk`.

On top of that we also add support for the `NO_COLOR` environment
variable as suggested by https://no-color.org/.

PR-URL: https://github.com/nodejs/node/pull/26485
Refs: https://github.com/nodejs/node/pull/26248
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

1 files changed, 39 insertions, 1 deletions

diff --git a/lib/internal/tty.js b/lib/internal/tty.js
index 486dbbeaa5..9c34d3fdb7 100644
--- a/lib/internal/tty.js
+++ b/lib/internal/tty.js
@@ -72,11 +72,49 @@ const TERM_ENVS_REG_EXP = [
   /^vt100/
 ];
 
+function warnOnDeactivatedColors(env) {
+  let name;
+  if (env.NODE_DISABLE_COLORS !== undefined)
+    name = 'NODE_DISABLE_COLORS';
+  if (env.NO_COLOR !== undefined)
+    name = 'NO_COLOR';
+
+  if (name !== undefined) {
+    process.emitWarning(
+      `The '${name}' env is ignored due to the 'FORCE_COLOR' env being set.`,
+      'Warning'
+    );
+  }
+}
+
 // The `getColorDepth` API got inspired by multiple sources such as
 // https://github.com/chalk/supports-color,
 // https://github.com/isaacs/color-support.
 function getColorDepth(env = process.env) {
-  if (env.NODE_DISABLE_COLORS || env.TERM === 'dumb') {
+  // Use level 0-3 to support the same levels as `chalk` does. This is done for
+  // consistency throughout the ecosystem.
+  if (env.FORCE_COLOR !== undefined) {
+    switch (env.FORCE_COLOR) {
+      case '':
+      case '1':
+      case 'true':
+        warnOnDeactivatedColors(env);
+        return COLORS_16;
+      case '2':
+        warnOnDeactivatedColors(env);
+        return COLORS_256;
+      case '3':
+        warnOnDeactivatedColors(env);
+        return COLORS_16m;
+      default:
+        return COLORS_2;
+    }
+  }
+
+  if (env.NODE_DISABLE_COLORS !== undefined ||
+      // See https://no-color.org/
+      env.NO_COLOR !== undefined ||
+      env.TERM === 'dumb') {
     return COLORS_2;
   }