lib: respect stream.isTTY=false in styleText even when FORCE_COLOR is set

When FORCE_COLOR is set (e.g. by
ode --test, which injects it into
child-process environments to colorize test output), the shouldColorize()
helper in lib/internal/util/colors.js was ignoring the isTTY property of
the stream argument entirely. This caused util.styleText() to apply ANSI
codes to streams that were explicitly marked as non-TTY by the caller.

Fix: if a stream is supplied and its isTTY property is explicitly false,
return false even when FORCE_COLOR is set. FORCE_COLOR is intended to
force color support in terminals that lie about their capabilities; it
should not override an explicit isTTY=false on a caller-supplied stream.

Fixes: #57921

Signed-off-by: piyushrajyadav <piyushyadavrajyadav@gmail.com>

Author: piyushrajyadav

lib/internal/util/colors.js

@@ -17,6 +17,12 @@ module.exports = {
   hasColors: false,
   shouldColorize(stream) {
     if (process.env.FORCE_COLOR !== undefined) {
+      // If a stream is explicitly provided and it is not a TTY, respect that
+      // even when FORCE_COLOR is set. FORCE_COLOR should not override an
+      // explicit isTTY=false on the stream passed by the caller.
+      if (stream?.isTTY === false) {
+        return false;
+      }
       return lazyInternalTTY().getColorDepth() > 2;
     }
     return stream?.isTTY && (

test/parallel/test-util-styletext.js

@@ -199,7 +199,10 @@ if (fd !== -1) {
     { isTTY: true, env: { NO_COLOR: '1' }, expected: noChange },
     { isTTY: true, env: { FORCE_COLOR: '1' }, expected: styled },
     { isTTY: true, env: { FORCE_COLOR: '1', NODE_DISABLE_COLORS: '1' }, expected: styled },
-    { isTTY: false, env: { FORCE_COLOR: '1', NO_COLOR: '1', NODE_DISABLE_COLORS: '1' }, expected: styled },
+    // When the stream is explicitly non-TTY, FORCE_COLOR must not override it.
+    // Regression test for https://github.com/nodejs/node/issues/57921
+    { isTTY: false, env: { FORCE_COLOR: '1' }, expected: noChange },
+    { isTTY: false, env: { FORCE_COLOR: '1', NO_COLOR: '1', NODE_DISABLE_COLORS: '1' }, expected: noChange },
     { isTTY: true, env: { FORCE_COLOR: '1', NO_COLOR: '1', NODE_DISABLE_COLORS: '1' }, expected: styled },
   ].forEach((testCase) => {
     writeStream.isTTY = testCase.isTTY;
@@ -221,3 +224,36 @@ if (fd !== -1) {
 } else {
   common.skip('Could not create TTY fd');
 }
+
+// Regression test for https://github.com/nodejs/node/issues/57921:
+// styleText() must honour stream.isTTY === false even when FORCE_COLOR is set
+// (e.g. as injected by `node --test` into child-process environments).
+{
+  const originalEnv = process.env;
+  process.env = { ...process.env, FORCE_COLOR: '1' };
+
+  // A plain object with isTTY=false — not a real WriteStream, but validateStream
+  // is false so the stream-type check is skipped; only isTTY is consulted.
+  const nonTTYStream = { isTTY: false };
+  assert.strictEqual(
+    util.styleText('red', 'test', { stream: nonTTYStream, validateStream: false }),
+    noChange,
+    'FORCE_COLOR should not override isTTY=false when a stream is supplied',
+  );
+
+  const ttyStream = { isTTY: true };
+  assert.strictEqual(
+    util.styleText('red', 'test', { stream: ttyStream, validateStream: false }),
+    styled,
+    'FORCE_COLOR should still enable color on isTTY=true streams',
+  );
+
+  // No stream provided — FORCE_COLOR should still work as before
+  assert.strictEqual(
+    util.styleText('red', 'test', { validateStream: false }),
+    styled,
+    'FORCE_COLOR should enable color when no stream constraint is set',
+  );
+
+  process.env = originalEnv;
+}