[FIX] website: fix install theme error

Commit 5a81d8883 fixed the COW view deletion on module update but introduced an
error when installing a theme.

Indeed, when installing a theme, the first step is to remove the currently
installed theme from the website (by unlinking its ir.ui.view).

Commit 5a81d8883 introduced the fact that deleting an ir.ui.view during a
module uninstall also search and delete the COW views, calling
`_get_specific_views` (that expects a singleton).

When installing a theme, it calls `_theme_cleanup` which search COW views and
unlink them. If not cow view, unlink is called with an empty record set raising
the singleton error.

closes odoo/odoo#31662

Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>

4 files changed, 21 insertions, 4 deletions

diff --git a/addons/test_website/tests/test_views_during_module_operation.py b/addons/test_website/tests/test_views_during_module_operation.py
index fceb71b5dc4..58cf943daf4 100644
--- a/addons/test_website/tests/test_views_during_module_operation.py
+++ b/addons/test_website/tests/test_views_during_module_operation.py
@@ -62,7 +62,7 @@ class TestViewsDuringModuleOperation(TransactionCase):
         self.assertTrue(self.env.ref(update_module_view_to_be_t_called.key))
         self.assertTrue(self.env.ref(update_module_base_view.key))
 
-        # Uninstall module
+        # Update the module
         test_website_module = self.env['ir.module.module'].search([('name', '=', 'test_website')])
         test_website_module.button_immediate_upgrade()
 
diff --git a/addons/website/models/ir_ui_view.py b/addons/website/models/ir_ui_view.py
index 90447640c41..d40204f7ff3 100644
--- a/addons/website/models/ir_ui_view.py
+++ b/addons/website/models/ir_ui_view.py
@@ -158,10 +158,12 @@ class View(models.Model):
                     # care of creating pages and menus.
                     view.with_context(website_id=website.id).write({'name': view.name})
 
-        if self.pool._init:
-            self += self._get_specific_views()
+        specific_views = self.env['ir.ui.view']
+        if self and self.pool._init:
+            for view in self:
+                specific_views += view._get_specific_views()
 
-        result = super(View, self).unlink()
+        result = super(View, self + specific_views).unlink()
         self.clear_caches()
         return result
 
diff --git a/addons/website_theme_install/tests/__init__.py b/addons/website_theme_install/tests/__init__.py
index 28efb5bbfb5..ae189cba198 100644
--- a/addons/website_theme_install/tests/__init__.py
+++ b/addons/website_theme_install/tests/__init__.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
+from . import test_theme
 from . import test_views
diff --git a/addons/website_theme_install/tests/test_theme.py b/addons/website_theme_install/tests/test_theme.py
new file mode 100644
index 00000000000..845474d67d2
--- /dev/null
+++ b/addons/website_theme_install/tests/test_theme.py
@@ -0,0 +1,14 @@
+# coding: utf-8
+from odoo.tests import common
+
+
+class TestTheme(common.TransactionCase):
+
+    def test_theme_remove_working(self):
+        """ This test ensure theme can be removed.
+        Theme removal is also the first step during theme installation.
+        """
+        theme_common_module = self.env['ir.module.module'].search([('name', '=', 'theme_default')])
+        website = self.env['website'].get_current_website()
+        website.theme_id = theme_common_module.id
+        self.env['ir.module.module']._theme_remove(website)