upgrades: Add diagnostic for held packages

- Add a new diagnostic check result for skipped tests.

Tests:

- Put a hold on a package. The diagnostic is failed.

- Remove the hold from the package. The diagnostic is passed.

- Start installing an app, then immediately run the upgrades
  diagnostics. The diagnostic is skipped.

Helps: #2347

Signed-off-by: James Valleroy <jvalleroy@mailbox.org>
[sunil: Allow i18n for new state 'skipped']
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/diagnostic_check.py

@@ -17,6 +17,7 @@ DiagnosticCheckParameters: TypeAlias = dict[str, str | int | bool | None]
 class Result(StrEnum):
     """The result of a diagnostic check."""
     NOT_DONE = 'not_done'
+    SKIPPED = 'skipped'
     PASSED = 'passed'
     WARNING = 'warning'
     FAILED = 'failed'

plinth/modules/diagnostics/__init__.py

@@ -96,6 +96,7 @@ def _run_on_all_enabled_modules():
 
     # Four result strings returned by tests, mark for translation and
     # translate later.
+    gettext_noop('skipped')
     gettext_noop('passed')
     gettext_noop('failed')
     gettext_noop('error')

plinth/modules/diagnostics/templates/diagnostics_results.html

@@ -23,6 +23,8 @@
               <span class="badge badge-danger">{% trans result.result %}</span>
             {% elif result.result == 'error' or result.result == 'warning' %}
               <span class="badge badge-warning">{% trans result.result %}</span>
+	    {% elif result.result == 'skipped' %}
+	      <span class="badge badge-secondary">{% trans result.result %}</span>
             {% else %}
               {{ result.result }}
             {% endif %}

plinth/modules/upgrades/__init__.py

@@ -11,9 +11,10 @@ from django.utils.translation import gettext_noop
 
 import plinth
 from plinth import app as app_module
-from plinth import cfg, glib, kvstore, menu
+from plinth import action_utils, cfg, glib, kvstore, menu, package
 from plinth.config import DropinConfigs
 from plinth.daemon import RelatedDaemon
+from plinth.diagnostic_check import DiagnosticCheck, Result
 from plinth.modules.backups.components import BackupRestore
 from plinth.package import Packages
 
@@ -159,6 +160,12 @@ class UpgradesApp(app_module.App):
         # install and on version increment.
         setup_repositories(None)
 
+    def diagnose(self) -> list[DiagnosticCheck]:
+        """Run diagnostics and return the results."""
+        results = super().diagnose()
+        results.append(_diagnose_held_packages())
+        return results
+
 
 def setup_repositories(_):
     """Setup apt repositories for backports."""
@@ -296,3 +303,19 @@ def test_dist_upgrade():
     """Test dist-upgrade from stable to testing."""
     if can_test_dist_upgrade():
         try_start_dist_upgrade(test=True)
+
+
+def _diagnose_held_packages():
+    """Check if any packages have holds."""
+    check = DiagnosticCheck('upgrades-package-holds',
+                            gettext_noop('Check for package holds'),
+                            Result.NOT_DONE)
+    if (package.is_package_manager_busy()
+            or action_utils.service_is_running('freedombox-dist-upgrade')):
+        check.result = Result.SKIPPED
+        return check
+
+    output = subprocess.check_output(['apt-mark', 'showhold']).decode().strip()
+    held_packages = output.split()
+    check.result = Result.FAILED if held_packages else Result.PASSED
+    return check