upgrades: Run dpkg/apt fixes before dist upgrade

Closes: #2490

Tests:

- Unit tests works.

- On a fresh stable container, enable auto updates. Run 'apt install
mumble-server' and kill the apt process when it is unpacking. After this any apt
install command will ask for running dpkg --configure -a. At this time, run the
Testing dist upgrade. Dist upgrade starts successfully and then shows the
message 'Fixing any broken apt/dpkg states...'. It also shows that packages that
were not setup have been setup. Dist upgrades proceeds after that.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/upgrades/distupgrade.py

@@ -223,6 +223,13 @@ def _apt_update():
     _apt_run(['update'])
 
 
+def _apt_fix():
+    """Try to fix any problems with apt/dpkg before the upgrade."""
+    logger.info('Fixing any broken apt/dpkg states...')
+    subprocess.run(['dpkg', '--configure', '-a'], check=False)
+    _apt_run(['--fix-broken', 'install'])
+
+
 def _apt_autoremove():
     """Run 'apt autoremove'."""
     logger.info('Running apt autoremove...')
@@ -298,6 +305,7 @@ def perform():
          _services_disable(), \
          _apt_hold_packages():
         _apt_update()
+        _apt_fix()
         _debconf_set_selections()
         _packages_remove_obsolete()
         _apt_full_upgrade()

plinth/modules/upgrades/tests/test_distupgrade.py

@@ -283,6 +283,17 @@ def test_apt_update(apt_run):
     apt_run.assert_called_with(['update'])
 
 
+@patch('plinth.modules.upgrades.distupgrade._apt_run')
+@patch('subprocess.run')
+def test_apt_fix(run, apt_run):
+    """Test that apt fixes work."""
+    distupgrade._apt_fix()
+    assert run.call_args_list == [
+        call(['dpkg', '--configure', '-a'], check=False)
+    ]
+    assert apt_run.call_args_list == [call(['--fix-broken', 'install'])]
+
+
 @patch('plinth.modules.upgrades.distupgrade._apt_run')
 def test_apt_autoremove(apt_run):
     """Test that apt autoremove works."""