tty: truecolor check moved before 256 check

256 color would be return instead of 16m if both env variables were set

* tty: improve color check order highest spec first
* tty: add test for TERM and COLORTERM set
* tty: move COLORTERM check outside TERM closure
* tty: remove extra if check for COLORTERM

Refs: #27609

PR-URL: #30474
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/tty.js

@@ -173,6 +173,10 @@ function getColorDepth(env = process.env) {
       return COLORS_256;
   }
 
+  if (env.COLORTERM === 'truecolor' || env.COLORTERM === '24bit') {
+    return COLORS_16m;
+  }
+
   if (env.TERM) {
     if (/^xterm-256/.test(env.TERM))
       return COLORS_256;
@@ -188,13 +192,10 @@ function getColorDepth(env = process.env) {
       }
     }
   }
-
+  // Move 16 color COLORTERM below 16m and 256
   if (env.COLORTERM) {
-    if (env.COLORTERM === 'truecolor' || env.COLORTERM === '24bit')
-      return COLORS_16m;
     return COLORS_16;
   }
-
   return COLORS_2;
 }
 

test/pseudo-tty/test-tty-color-support.js

@@ -71,6 +71,7 @@ const writeStream = new WriteStream(fd);
   [{ NO_COLOR: '', COLORTERM: '24bit' }, 1],
   [{ TMUX: '1', FORCE_COLOR: 0 }, 1],
   [{ NO_COLOR: 'true', FORCE_COLOR: 0, COLORTERM: 'truecolor' }, 1],
+  [{ TERM: 'xterm-256color', COLORTERM: 'truecolor' }, 24],
 ].forEach(([env, depth], i) => {
   const actual = writeStream.getColorDepth(env);
   assert.strictEqual(