[FIX] base: when saving settings, only reset environment if modules were installed/uninstalled

Execute the tests from ea574fe9ff644 and 9e9ac5ced80b30,
which are in a SavepointCase.
The second test fails on a cache_miss.
Whats happens is the following:
 - the second test starts with the environment from the beginning of the
   first test. However its envs has a reference to environments that
   were created during the first test.
 - when computing the field, the ORM finds the value in a zombie
   environment, so does not recompute it
 - when trying to get the value, the value is not in cache

The issue is that going through res.config.settings's execute resets the
envs.

One solution is to put:
    self.addCleanup(lambda: setattr(self.env.envs, 'envs', envs))
in SavepointCase's setup.

However in that case the reset is not needed at all:
it's necessary only if there were some modules to install.
Unfortunately to_install and to_uninstall are not symmetric:
to_uninstall contains only modules that should be uninstalled, whereas
to_install contains everything, and only filters later what actions
really need to be performed.

In this case, we can rely on the result of the installation process.

closes odoo/odoo#41126

Signed-off-by: Nans Lefebvre (len) <len@odoo.com>

addons/base_setup/tests/test_res_config.py

@@ -1,11 +1,25 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
+from unittest.mock import patch
 from odoo.tests.common import TransactionCase
 
 
+def just_raise(*args):
+    raise Exception("We should not be here.")
+
+
 class TestResConfig(TransactionCase):
 
+    def setUp(self):
+        super(TestResConfig, self).setUp()
+
+        self.user = self.env.ref('base.user_admin')
+        self.company = self.env['res.company'].create({'name': 'oobO'})
+        self.user.write({'company_ids': [(4, self.company.id)], 'company_id': self.company.id})
+        Settings = self.env['res.config.settings'].with_user(self.user.id)
+        self.config = Settings.create({})
+
     def test_multi_company_res_config_group(self):
         # Enable/Disable a group in a multi-company environment
         # 1/ All the users should be added/removed from the group
@@ -53,3 +67,30 @@ class TestResConfig(TransactionCase):
             'partner_id': new_partner.id,
         })
         self.assertTrue(new_user not in self.env.ref('base.group_multi_currency').sudo().users)
+
+    def test_no_install(self):
+        """Make sure that when saving settings,
+           no modules are installed if nothing was set to install.
+        """
+        # check that no module should be installed in the first place
+        config_fields = self.config._get_classified_fields()
+        for name, module in config_fields['module']:
+            if int(self.config[name]):
+                self.assertTrue(module.state != 'uninstalled',
+                                "All set modules should already be installed.")
+        # if we try to install something, raise; so nothing should be installed
+        with patch('odoo.addons.base.models.ir_module.Module._button_immediate_function', new=just_raise):
+            self.config.execute()
+
+    def test_install(self):
+        """Make sure that the previous test is valid, i.e. when saving settings,
+           it starts module install if something was set to install.
+        """
+        config_fields = self.config._get_classified_fields()
+        # set the first uninstalled module to install
+        module_to_install = next(filter(lambda m: m[1].state == 'uninstalled', config_fields['module']))
+        self.config[module_to_install[0]] = True
+
+        with patch('odoo.addons.base.models.ir_module.Module._button_immediate_function', new=just_raise):
+            with self.assertRaisesRegex(Exception, "We should not be here."):
+                self.config.execute()

odoo/addons/base/models/res_config.py

@@ -627,10 +627,9 @@ class ResConfigSettings(models.TransientModel, ResConfigModuleInstallationMixin)
         if to_uninstall_modules:
             to_uninstall_modules.button_immediate_uninstall()
 
-        self._install_modules(to_install)
+        installation_status = self._install_modules(to_install)
 
-
-        if to_install or to_uninstall_modules:
+        if installation_status or to_uninstall_modules:
             # After the uninstall/install calls, the registry and environments
             # are no longer valid. So we reset the environment.
             self.env.reset()