[Tool] Output help on 'flutter pub' (#126211) This change makes `flutter pub` show the help usage: ``` PS > flutter pub Commands for managing Flutter packages. Global options: -h, --help Print this usage information. -v, --verbose Noisy logging, including all shell commands executed. If used with "--help", shows hidden options. If used with "flutter doctor", shows additional diagnostic information. (Use "-vv" to force verbose logging in those cases.) -d, --device-id Target device id or name (prefixes allowed). --version Reports the version of this tool. --suppress-analytics Suppress analytics reporting for the current CLI invocation. --disable-telemetry Disable telemetry reporting when this command runs. Usage: flutter pub <subcommand> [arguments] -h, --help Print this usage information. Available subcommands: add Add a dependency to pubspec.yaml. cache Work with the Pub system cache. deps Print package dependencies. downgrade Downgrade packages in a Flutter project. get Get the current package's dependencies. global Work with Pub global packages. login Log into pub.dev. logout Log out of pub.dev. outdated Analyze dependencies to find which ones can be upgraded. pub Pass the remaining arguments to Dart's "pub" tool. publish Publish the current package to pub.dartlang.org. remove Removes a dependency from the current package. run Run an executable from a package. test Run the "test" package. token Manage authentication tokens for hosted pub repositories. upgrade Upgrade the current package's dependencies to latest versions. uploader Manage uploaders for a package on pub.dev. version Print Pub version. Run "flutter help" to see global options. ``` Previously it showed an error message: ``` PS > flutter pub Missing subcommand for "flutter pub". Run 'flutter -h' (or 'flutter <command> -h') for available flutter commands and options. ``` Addresses https://github.com/flutter/flutter/issues/110025

diff --git a/packages/flutter_tools/lib/src/commands/custom_devices.dart b/packages/flutter_tools/lib/src/commands/custom_devices.dart
index 30d801e..7fda27a 100644
--- a/packages/flutter_tools/lib/src/commands/custom_devices.dart
+++ b/packages/flutter_tools/lib/src/commands/custom_devices.dart

@@ -123,7 +123,7 @@
 
   final CustomDevicesConfig _customDevicesConfig;
   final FeatureFlags _featureFlags;
-  final void Function(Object) _usagePrintFn;
+  final PrintFn _usagePrintFn;
 
   @override
   String get description {

diff --git a/packages/flutter_tools/lib/src/commands/packages.dart b/packages/flutter_tools/lib/src/commands/packages.dart
index 448bbbe..03ebd68 100644
--- a/packages/flutter_tools/lib/src/commands/packages.dart
+++ b/packages/flutter_tools/lib/src/commands/packages.dart

@@ -18,8 +18,14 @@
 import '../reporting/reporting.dart';
 import '../runner/flutter_command.dart';
 
+/// The function signature of the [print] function.
+typedef PrintFn = void Function(Object?);
+
 class PackagesCommand extends FlutterCommand {
-  PackagesCommand() {
+  PackagesCommand({
+    PrintFn usagePrintFn = print,
+  }) : _usagePrintFn = usagePrintFn
+  {
     addSubcommand(PackagesGetCommand('get', "Get the current package's dependencies.", PubContext.pubGet));
     addSubcommand(PackagesGetCommand('upgrade', "Upgrade the current package's dependencies to latest versions.", PubContext.pubUpgrade));
     addSubcommand(PackagesGetCommand('add', 'Add a dependency to pubspec.yaml.', PubContext.pubAdd));
@@ -40,6 +46,8 @@
     addSubcommand(PackagesPassthroughCommand());
   }
 
+  final PrintFn _usagePrintFn;
+
   @override
   final String name = 'pub';
 
@@ -54,6 +62,9 @@
 
   @override
   Future<FlutterCommandResult> runCommand() async => FlutterCommandResult.fail();
+
+  @override
+  void printUsage() => _usagePrintFn(usage);
 }
 
 class PackagesTestCommand extends FlutterCommand {

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
index 5c31c8d..ea84a7d 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart

@@ -176,13 +176,16 @@
 
   @override
   Future<void> run(Iterable<String> args) {
-    // Have an invocation of 'build' print out it's sub-commands.
+    // Have invocations of 'build', 'custom-devices', and 'pub' print out
+    // their sub-commands.
     // TODO(ianh): Move this to the Build command itself somehow.
     if (args.length == 1) {
       if (args.first == 'build') {
         args = <String>['build', '-h'];
       } else if (args.first == 'custom-devices') {
         args = <String>['custom-devices', '-h'];
+      } else if (args.first == 'pub') {
+        args = <String>['pub', '-h'];
       }
     }
 

diff --git a/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/pub_test.dart
similarity index 95%
rename from packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart
rename to packages/flutter_tools/test/commands.shard/hermetic/pub_test.dart
index 657adfd..d482cf8 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/pub_get_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/pub_test.dart

@@ -30,6 +30,20 @@
     Cache.enableLocking();
   });
 
+  testUsingContext('pub shows help', () async {
+    Object? usage;
+    final PackagesCommand command = PackagesCommand(
+      usagePrintFn: (Object? object) => usage = object,
+    );
+    final CommandRunner<void> runner = createTestCommandRunner(command);
+    await runner.run(<String>['pub']);
+
+    expect(usage, allOf(
+      contains('Commands for managing Flutter packages.'),
+      contains('Usage: flutter pub <subcommand> [arguments]'),
+    ));
+  });
+
   testUsingContext('pub get usage values are resilient to missing package config files before running "pub get"', () async {
     fileSystem.currentDirectory.childFile('pubspec.yaml').createSync();
     fileSystem.currentDirectory.childFile('.flutter-plugins').createSync();