[tool] Conditionalize color on stdout (#4436)

Refactors colorization to a centralized utility file, and makes it all conditional on `stdout` having ANSI escape support. This makes the output more readable on LUCI, which unlike the Cirrus log display doesn't handle ANSI.

Fixes https://github.com/flutter/flutter/issues/89392

script/tool/test/common/output_utils_test.dart

@@ -0,0 +1,100 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:flutter_plugin_tools/src/common/output_utils.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('with color support', () {
+    setUp(() {
+      useColorForOutput = true;
+    });
+
+    tearDown(() {
+      useColorForOutput = stdout.supportsAnsiEscapes;
+    });
+
+    test('colorize works', () async {
+      const String message = 'a message';
+
+      expect(
+          colorizeString(message, Styles.MAGENTA), '\x1B[35m$message\x1B[0m');
+    });
+
+    test('printSuccess is green', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printSuccess(message)),
+          '\x1B[32m$message\x1B[0m');
+    });
+
+    test('printWarning is yellow', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printWarning(message)),
+          '\x1B[33m$message\x1B[0m');
+    });
+
+    test('printError is red', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printError(message)),
+          '\x1B[31m$message\x1B[0m');
+    });
+  });
+
+  group('without color support', () {
+    setUp(() {
+      useColorForOutput = false;
+    });
+
+    tearDown(() {
+      useColorForOutput = stdout.supportsAnsiEscapes;
+    });
+
+    test('colorize no-ops', () async {
+      const String message = 'a message';
+
+      expect(colorizeString(message, Styles.MAGENTA), message);
+    });
+
+    test('printSuccess just prints', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printSuccess(message)), message);
+    });
+
+    test('printWarning just prints', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printWarning(message)), message);
+    });
+
+    test('printError just prints', () async {
+      const String message = 'a message';
+
+      expect(await _capturePrint(() => printError(message)), message);
+    });
+  });
+}
+
+/// Run the command [runner] with the given [args] and return
+/// what was printed.
+/// A custom [errorHandler] can be used to handle the runner error as desired without throwing.
+Future<String> _capturePrint(void Function() printFunction) async {
+  final StringBuffer output = StringBuffer();
+  final ZoneSpecification spec = ZoneSpecification(
+    print: (_, __, ___, String message) {
+      output.write(message);
+    },
+  );
+  await Zone.current
+      .fork(specification: spec)
+      .run<Future<void>>(() async => printFunction());
+
+  return output.toString();
+}

script/tool/test/common/package_looping_command_test.dart

@@ -9,6 +9,7 @@ import 'package:args/command_runner.dart';
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_plugin_tools/src/common/core.dart';
+import 'package:flutter_plugin_tools/src/common/output_utils.dart';
 import 'package:flutter_plugin_tools/src/common/package_looping_command.dart';
 import 'package:mockito/mockito.dart';
 import 'package:test/test.dart';
@@ -82,6 +83,8 @@ void main() {
   late Directory thirdPartyPackagesDir;
 
   setUp(() {
+    // Correct color handling is part of the behavior being tested here.
+    useColorForOutput = true;
     fileSystem = MemoryFileSystem();
     mockPlatform = MockPlatform();
     packagesDir = createPackagesDirectory(fileSystem: fileSystem);
@@ -90,6 +93,11 @@ void main() {
         .childDirectory('packages');
   });
 
+  tearDown(() {
+    // Restore the default behavior.
+    useColorForOutput = io.stdout.supportsAnsiEscapes;
+  });
+
   /// Creates a TestPackageLoopingCommand instance that uses [gitDiffResponse]
   /// for git diffs, and logs output to [printOutput].
   TestPackageLoopingCommand createTestCommand({

script/tool/test/publish_command_test.dart

@@ -525,8 +525,8 @@ void main() {
                 'Publishing all packages that have changed relative to "HEAD~"'),
             contains('Running `pub publish ` in ${plugin1.path}...'),
             contains('Running `pub publish ` in ${plugin2.path}...'),
-            contains('plugin1 - \x1B[32mpublished\x1B[0m'),
-            contains('plugin2/plugin2 - \x1B[32mpublished\x1B[0m'),
+            contains('plugin1 - published'),
+            contains('plugin2/plugin2 - published'),
           ]));
       expect(
           processRunner.recordedCalls,