[FIX] expression: properly handle {TRUE,FALSE}_LEAF

Before this commit, doing expression.OR() with only FALSE_LEAF would
yield [] which is equivalent to TRUE_LEAF and is therefore not correct.

The same happened (to a lesser extent) with expression.AND() within an
expression.OR(), since the former would return a [] which would be
ignored by expression.OR().

See tests for a clearer view of the use cases.

Fixes #30113, #26540

closes odoo/odoo#31202

odoo/addons/base/tests/test_expression.py

@@ -612,6 +612,36 @@ class TestExpression(TransactionCase):
         not_be = Partner.with_context(lang='fr_FR').search([('country_id', '!=', 'Belgique')])
         self.assertNotIn(agrolait, not_be)
 
+    def test_proper_combine_unit_leaves(self):
+        # test that unit leaves (TRUE_LEAF, FALSE_LEAF) are properly handled in specific cases
+        false = expression.FALSE_DOMAIN
+        true = expression.TRUE_DOMAIN
+        normal = [('foo', '=', 'bar')]
+        # OR with single FALSE_LEAF
+        expr = expression.OR([false])
+        self.assertEqual(expr, false)
+        # OR with multiple FALSE_LEAF
+        expr = expression.OR([false, false])
+        self.assertEqual(expr, false)
+        # OR with FALSE_LEAF and a normal leaf
+        expr = expression.OR([false, normal])
+        self.assertEqual(expr, normal)
+        # OR with AND of single TRUE_LEAF and normal leaf
+        expr = expression.OR([expression.AND([true]), normal])
+        self.assertEqual(expr, true)
+        # AND with single TRUE_LEAF
+        expr = expression.AND([true])
+        self.assertEqual(expr, true)
+        # AND with multiple TRUE_LEAF
+        expr = expression.AND([true, true])
+        self.assertEqual(expr, true)
+        # AND with TRUE_LEAF and normal leaves
+        expr = expression.AND([true, normal])
+        self.assertEqual(expr, normal)
+        # AND with OR with single FALSE_LEAF and normal leaf
+        expr = expression.AND([expression.OR([false]), normal])
+        self.assertEqual(expr, false)
+
 
 class TestAutoJoin(TransactionCase):
 

odoo/osv/expression.py

@@ -233,7 +233,7 @@ def combine(operator, unit, zero, domains):
             result += domain
             count += 1
     result = [operator] * (count - 1) + result
-    return result
+    return result or unit
 
 
 def AND(domains):