Fix: Prevent color-forcing env vars from being forwarded when stdout is not a TTY

This fixes a bug where FORCE_COLOR, NO_COLOR, CLICOLOR, and CLICOLOR_FORCE
were being forwarded from the host environment into containers even when
stdout was redirected. This undermined the ANSI-leak fix by causing tools
to emit ANSI escape codes despite the absence of a TTY.

The fix conditionally skips forwarding these color-forcing variables when
stdout is not a TTY, preventing ANSI codes from appearing in redirected
output (e.g., 'lando composer show > file.txt').

User-provided environment variables (via userEnv parameter) still override
this behavior, preserving explicit user intent.

Author: cursoragent

test/build-exec-environment.spec.js

@@ -64,6 +64,27 @@ describe('build-exec-environment', () => {
       const env = buildEnvironment(ctx);
       expect(env.TZ).to.equal('America/New_York');
     });
+
+    it('should not forward FORCE_COLOR when stdout is not a TTY', () => {
+      process.env.FORCE_COLOR = '1';
+      const ctx = {stdout: {isTTY: false, columns: 80, rows: 24}, stderr: {isTTY: false}, noColor: false};
+      const env = buildEnvironment(ctx);
+      expect(env).to.not.have.property('FORCE_COLOR');
+    });
+
+    it('should not forward NO_COLOR when stdout is not a TTY', () => {
+      process.env.NO_COLOR = '1';
+      const ctx = {stdout: {isTTY: false, columns: 80, rows: 24}, stderr: {isTTY: false}, noColor: false};
+      const env = buildEnvironment(ctx);
+      expect(env).to.not.have.property('NO_COLOR');
+    });
+
+    it('should forward FORCE_COLOR when stdout is a TTY', () => {
+      process.env.FORCE_COLOR = '1';
+      const ctx = {stdout: {isTTY: true}, stderr: {isTTY: true}, noColor: false};
+      const env = buildEnvironment(ctx);
+      expect(env.FORCE_COLOR).to.equal('1');
+    });
   });
 
   describe('synthetic vars', () => {
@@ -88,11 +109,12 @@ describe('build-exec-environment', () => {
       expect(env).to.not.have.property('CLICOLOR_FORCE');
     });
 
-    it('should not override inherited CLICOLOR_FORCE with synthetic', () => {
+    it('should not forward CLICOLOR_FORCE when stdout is not a TTY', () => {
       process.env.CLICOLOR_FORCE = '3';
       const ctx = {stdout: {isTTY: false, columns: 80, rows: 24}, stderr: {isTTY: true}, noColor: false};
       const env = buildEnvironment(ctx);
-      expect(env.CLICOLOR_FORCE).to.equal('3');
+      // Color-forcing vars are skipped when stdout is not a TTY to prevent ANSI leakage
+      expect(env).to.not.have.property('CLICOLOR_FORCE');
     });
   });
 

utils/build-exec-environment.js

@@ -23,7 +23,12 @@ const forwardKeys = [
 module.exports = (context, userEnv = {}) => {
   const inherited = {};
   for (const key of forwardKeys) {
-    if (process.env[key] !== undefined) inherited[key] = process.env[key];
+    if (process.env[key] !== undefined) {
+      // Skip color-forcing vars when stdout is not a TTY to prevent ANSI leakage
+      const colorVars = ['NO_COLOR', 'FORCE_COLOR', 'CLICOLOR', 'CLICOLOR_FORCE'];
+      if (!context.stdout.isTTY && colorVars.includes(key)) continue;
+      inherited[key] = process.env[key];
+    }
   }
 
   const synthetic = {};