package: Add functions for removing packages

Functions needed to spot and remove installed conflicting packages
before installation of apps.

- Remove all packages in a single operation as this way apt can search for
solutions to conflicts more easily.

- Use type hints rather than a lot of type checking. Type hints shall later be
enforced using offline checking (with mypy) or at runtime (with enforce, etc.).

Signed-off-by: Fioddor Superconcentrado <fioddor@gmail.com>
[sunil: Run single remove operation on all packages]
[sunil: Use type hints instead of extensive type checking]
[sunil: Trim down the test case as it would only succeed after install]
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

package

actions/packages

@@ -48,6 +48,11 @@ def parse_arguments():
         'module', help='name of module for which package is being installed')
     subparser.add_argument('packages', nargs='+',
                            help='list of packages to install')
+
+    subparser = subparsers.add_parser('remove', help='remove the package(s)')
+    subparser.add_argument('--packages', required=True,
+                           help='List of packages to remove', nargs='+')
+
     subparsers.add_parser('is-package-manager-busy',
                           help='Return whether package manager is busy')
     subparser = subparsers.add_parser(
@@ -100,6 +105,11 @@ def subcommand_install(arguments):
     sys.exit(returncode)
 
 
+def subcommand_remove(arguments):
+    """Remove apt package(s)."""
+    sys.exit(run_apt_command(['remove'] + arguments.packages))
+
+
 def _assert_managed_packages(module, packages):
     """Check that list of packages are in fact managed by module."""
     cfg.read()
@@ -116,7 +126,8 @@ def _assert_managed_packages(module, packages):
 def subcommand_is_package_manager_busy(_):
     """Check whether package manager is busy.
 
-    An exit code of zero indicates that package manager is busy."""
+    An exit code of zero indicates that package manager is busy.
+    """
     if not is_package_manager_busy():
         sys.exit(-1)
 

plinth/package.py

@@ -7,11 +7,14 @@ import json
 import logging
 import subprocess
 import threading
+from typing import Union
 
+import apt.cache
 from django.utils.translation import gettext as _
 from django.utils.translation import gettext_lazy
 
 from plinth import actions
+from plinth.errors import ActionError, PlinthError
 from plinth.utils import format_lazy
 
 logger = logging.getLogger(__name__)
@@ -195,3 +198,30 @@ def filter_conffile_prompt_packages(packages):
         'packages',
         ['filter-conffile-packages', '--packages'] + list(packages))
     return json.loads(response)
+
+
+def packages_installed(candidates: Union[list, tuple]) -> list:
+    """Check which candidates are installed on the system.
+
+    :param candidates: A list of package names.
+    :return: A list of installed Debian package names.
+    """
+    cache = apt.cache.Cache()
+    installed_packages = []
+    for package_name in candidates:
+        try:
+            package = cache[package_name]
+            if package.is_installed:
+                installed_packages.append(package_name)
+        except KeyError:
+            pass
+
+    return installed_packages
+
+
+def remove(packages: Union[list, tuple]) -> None:
+    """Remove packages."""
+    try:
+        actions.superuser_run('packages', ['remove', '--packages'] + packages)
+    except ActionError:
+        pass

plinth/tests/test_package.py

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""
+Test module for package module.
+"""
+
+from unittest.mock import call, patch
+
+from plinth.errors import ActionError
+from plinth.package import packages_installed, remove
+
+
+def test_packages_installed():
+    """Test packages_installed()."""
+    # list as input
+    assert len(packages_installed([])) == 0
+    assert len(packages_installed(['unknown-package'])) == 0
+    assert len(packages_installed(['python3'])) == 1
+    # tuples as input
+    assert len(packages_installed(())) == 0
+    assert len(packages_installed(('unknown-package', ))) == 0
+    assert len(packages_installed(('python3', ))) == 1
+
+
+@patch('plinth.actions.superuser_run')
+def test_remove(run):
+    """Test removing packages."""
+    remove(['package1', 'package2'])
+    run.assert_has_calls(
+        [call('packages', ['remove', '--packages', 'package1', 'package2'])])
+
+    run.reset_mock()
+    run.side_effect = ActionError()
+    remove(['package1'])
+    run.assert_has_calls(
+        [call('packages', ['remove', '--packages', 'package1'])])