[FIX] osv: fix combination of unit domain

Combining a list of elements containing only the monoid's unit should return the
unit.

Since the unit is skipped, it would return an empty domain instead of the unit,
meaning that (0, '=', 1) could not be used in a group rule.

To test this, create a record rule on a model M with domain (0, '=', 1)
that applies to group G.
Log in with a user in group G and access model M; you can read everything
(provided no other record rule applies) whereas you should see nothing.

Because of expression.AND(global_domains + [expression.OR(group_domains)])
we want the empty domain to still be left untouched, even if it violates
the OR's unit rules (i.e. OR(empty, OR(R)) = OR(R) <=> OR(empty) = unit).
Meaning that no group rule would reduce to having a (0, '=' 1) group rule.
So in the end we don't really care about all that algebraic nonsense.

closes odoo/odoo#28765

1 files changed, 2 insertions, 0 deletions

diff --git a/odoo/osv/expression.py b/odoo/osv/expression.py
index 483f325322c..f5518fead94 100644
--- a/odoo/osv/expression.py
+++ b/odoo/osv/expression.py
@@ -251,6 +251,8 @@ def combine(operator, unit, zero, domains):
     """
     result = []
     count = 0
+    if domains == [unit]:
+        return unit
     for domain in domains:
         if domain == unit:
             continue