[CLI] Migrate package (#5060)

### Changes

This PR adds the new `casp package` command to the `casp` CLI. Which
acts as a convenient wrapper for the root `butler.py package` script.

### How it works:
- `casp package` packages ClusterFuzz with a staging revision.
- `casp package -p <platform>` specifies the target platform (`linux`,
`macos`, `windows`, or `all`).
- `casp package -r <release>` sets the release channel (options: `prod`,
`candidate`, or `chrome-tests-syncer`).
- If `-r` is not provided, the release channel defaults to `prod`.

### Changes in butler

Regarding the refactor/improvement in `butler.py`, here are some
screenshots comparing running `python butler.py package` in this branch
and master. They show that the behavior is the same.
<img width="1438" height="233" alt="image"
src="https://github.com/user-attachments/assets/b33a65ae-e816-4bbe-a531-4c80f3aff62d"
/>
<img width="1438" height="234" alt="image"
src="https://github.com/user-attachments/assets/cef26580-2bdf-416b-8822-25e008ea2893"
/>

<img width="1438" height="233" alt="image"
src="https://github.com/user-attachments/assets/271b09e6-14cd-4122-a72a-e8908557ff6c"
/>
<img width="1438" height="234" alt="image"
src="https://github.com/user-attachments/assets/fa1d3b03-6332-488f-9931-74542d26bdd4"
/>


### Demo prints

Here are some screenshots of `casp package` in action:

* `casp package -p linux`
<img width="1438" height="233" alt="image"
src="https://github.com/user-attachments/assets/1aa540cf-4211-40a0-b074-4bf6dd7905fd"
/>
<img width="1438" height="234" alt="image"
src="https://github.com/user-attachments/assets/278595f9-b1eb-4cbc-a5bd-58ced2b5816f"
/>

Author: PauloVLB

butler.py

@@ -98,6 +98,19 @@ def _setup_args_for_remote(parser):
   subparsers.add_parser('reboot', help='Reboot with `sudo reboot`.')
 
 
+def _add_package_subparser(toplevel_subparsers):
+  """Adds a parser for the `package` command."""
+  parser_package = toplevel_subparsers.add_parser(
+      'package', help='Package clusterfuzz with a staging revision')
+  parser_package.add_argument(
+      '-p', '--platform', choices=['linux', 'macos', 'windows', 'all'])
+  parser_package.add_argument(
+      '-r',
+      '--release',
+      choices=['prod', 'candidate', 'chrome-tests-syncer'],
+      default='prod')
+
+
 def _add_bootstrap_subparser(toplevel_subparsers):
   """Adds a parser for the `bootstrap` command."""
   toplevel_subparsers.add_parser(
@@ -334,16 +347,6 @@ def main():
       help=('Do not close browser when tests '
             'finish. Good for debugging.'))
 
-  parser_package = subparsers.add_parser(
-      'package', help='Package clusterfuzz with a staging revision')
-  parser_package.add_argument(
-      '-p', '--platform', choices=['linux', 'macos', 'windows', 'all'])
-  parser_package.add_argument(
-      '-r',
-      '--release',
-      choices=['prod', 'candidate', 'chrome-tests-syncer'],
-      default='prod')
-
   parser_deploy = subparsers.add_parser('deploy', help='Deploy to Appengine')
   parser_deploy.add_argument(
       '-f',
@@ -457,6 +460,7 @@ def main():
       default='us-central',
       help='Location for App Engine.')
 
+  _add_package_subparser(subparsers)
   _add_bootstrap_subparser(subparsers)
   _add_py_unittest_subparser(subparsers)
   _add_lint_subparser(subparsers)

cli/casp/src/casp/commands/package.py

@@ -13,11 +13,47 @@
 # limitations under the License.
 """Package command."""
 
+import subprocess
+import sys
+
+from casp.utils import local_butler
 import click
 
 
 @click.command(
-    name='package', help='Package clusterfuzz with a staging revision')
-def cli():
+    name='package',
+    help=('Package clusterfuzz with a staging revision. '
+          'It creates a zip for each platform chosen in '
+          'the clusterfuzz/deployment directory.'))
+@click.option(
+    '--platform',
+    '-p',
+    type=click.Choice(['linux', 'macos', 'windows', 'all']),
+    help='The platform to package for.')
+@click.option(
+    '--release',
+    '-r',
+    type=click.Choice(['prod', 'candidate', 'chrome-tests-syncer']),
+    default='prod',
+    show_default=True,
+    help='The release channel.')
+def cli(platform, release):
   """Package clusterfuzz with a staging revision"""
-  click.echo('To be implemented...')
+  try:
+    arguments = {'release': release}
+    if platform:
+      arguments['platform'] = platform
+
+    command = local_butler.build_command('package', **arguments)
+  except FileNotFoundError:
+    click.echo('butler.py not found in this directory.', err=True)
+    sys.exit(1)
+
+  try:
+    subprocess.run(command, check=True)
+  except FileNotFoundError:
+    click.echo('python not found in PATH.', err=True)
+    sys.exit(1)
+  except subprocess.CalledProcessError as e:
+    click.echo(f'Error running butler.py package: {e}', err=True)
+    sys.exit(1)

cli/casp/src/casp/tests/commands/package_test.py

@@ -0,0 +1,83 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Tests for the package command.
+
+  For running all the tests, use (from the root of the project):
+  python -m unittest discover -s cli/casp/src/casp/tests -p package_test.py -v
+"""
+
+import subprocess
+import unittest
+from unittest.mock import patch
+
+from casp.commands import package as package_command
+from click.testing import CliRunner
+
+
+class PackageCliTest(unittest.TestCase):
+  """Tests for the package command."""
+
+  def setUp(self):
+    self.runner = CliRunner()
+    self.mock_local_butler = self.enterContext(
+        patch('casp.commands.package.local_butler', autospec=True))
+    self.mock_subprocess_run = self.enterContext(
+        patch('subprocess.run', autospec=True))
+
+  def test_package_success_defaults(self):
+    """Tests package command with defaults."""
+    self.mock_local_butler.build_command.return_value = ['cmd']
+    result = self.runner.invoke(package_command.cli)
+    self.assertEqual(0, result.exit_code, msg=result.output)
+    self.mock_local_butler.build_command.assert_called_once_with(
+        'package', release='prod')
+    self.mock_subprocess_run.assert_called_once_with(['cmd'], check=True)
+
+  def test_package_success_with_args(self):
+    """Tests package command with arguments."""
+    self.mock_local_butler.build_command.return_value = ['cmd']
+    result = self.runner.invoke(
+        package_command.cli, ['--platform', 'linux', '--release', 'candidate'])
+    self.assertEqual(0, result.exit_code, msg=result.output)
+    self.mock_local_butler.build_command.assert_called_once_with(
+        'package', platform='linux', release='candidate')
+
+  def test_butler_not_found(self):
+    """Tests when butler.py is not found."""
+    self.mock_local_butler.build_command.side_effect = FileNotFoundError
+    result = self.runner.invoke(package_command.cli)
+    self.assertNotEqual(0, result.exit_code)
+    self.assertIn('butler.py not found', result.output)
+    self.mock_subprocess_run.assert_not_called()
+
+  def test_subprocess_run_fails(self):
+    """Tests when subprocess.run fails."""
+    self.mock_local_butler.build_command.return_value = ['cmd']
+    self.mock_subprocess_run.side_effect = subprocess.CalledProcessError(
+        1, 'cmd')
+    result = self.runner.invoke(package_command.cli)
+    self.assertNotEqual(0, result.exit_code)
+    self.assertIn('Error running butler.py package', result.output)
+
+  def test_python_not_found(self):
+    """Tests when python command is not found."""
+    self.mock_local_butler.build_command.return_value = ['cmd']
+    self.mock_subprocess_run.side_effect = FileNotFoundError
+    result = self.runner.invoke(package_command.cli)
+    self.assertNotEqual(0, result.exit_code)
+    self.assertIn('python not found in PATH', result.output)
+
+
+if __name__ == '__main__':
+  unittest.main()