Fixed #32673 -- Fixed lookups crash when comparing against lookups on PostgreSQL.

Regression in 3a505c70e7.

Nonlitteral right-hand-sides of lookups need to be wrapped in
parentheses to avoid operator precedence ambiguities.

Thanks Charles Lirsac for the detailed report.

django/db/backends/oracle/features.py

@@ -87,6 +87,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         'Raises ORA-00600: internal error code.': {
             'model_fields.test_jsonfield.TestQuerying.test_usage_in_subquery',
         },
+        "Oracle doesn't allow filters to be compared to another expression in "
+        "the WHERE clause.": {
+            'lookup.tests.LookupTests.test_lookup_rhs',
+        },
     }
     django_test_expected_failures = {
         # A bug in Django/cx_Oracle with respect to string handling (#23843).

django/db/models/lookups.py

@@ -94,7 +94,13 @@ class Lookup:
             value = self.apply_bilateral_transforms(value)
             value = value.resolve_expression(compiler.query)
         if hasattr(value, 'as_sql'):
-            return compiler.compile(value)
+            sql, params = compiler.compile(value)
+            # Ensure expression is wrapped in parentheses to respect operator
+            # precedence but avoid double wrapping as it can be misinterpreted
+            # on some backends (e.g. subqueries on SQLite).
+            if sql and sql[0] != '(':
+                sql = '(%s)' % sql
+            return sql, params
         else:
             return self.get_db_prep_lookup(value, connection)
 

tests/lookup/models.py

@@ -94,6 +94,7 @@ class Product(models.Model):
 
 class Stock(models.Model):
     product = models.ForeignKey(Product, models.CASCADE)
+    short = models.BooleanField(default=False)
     qty_available = models.DecimalField(max_digits=6, decimal_places=2)
 
 

tests/lookup/tests.py

@@ -5,13 +5,16 @@ from operator import attrgetter
 
 from django.core.exceptions import FieldError
 from django.db import connection, models
-from django.db.models import Exists, Max, OuterRef
+from django.db.models import (
+    BooleanField, Exists, ExpressionWrapper, F, Max, OuterRef, Q,
+)
 from django.db.models.functions import Substr
 from django.test import TestCase, skipUnlessDBFeature
 from django.test.utils import isolate_apps
 
 from .models import (
-    Article, Author, Freebie, Game, IsNullWithNoneAsRHS, Player, Season, Tag,
+    Article, Author, Freebie, Game, IsNullWithNoneAsRHS, Player, Product,
+    Season, Stock, Tag,
 )
 
 
@@ -1000,3 +1003,20 @@ class LookupTests(TestCase):
             with self.subTest(qs=qs):
                 with self.assertRaisesMessage(ValueError, msg):
                     qs.exists()
+
+    def test_lookup_rhs(self):
+        product = Product.objects.create(name='GME', qty_target=5000)
+        stock_1 = Stock.objects.create(product=product, short=True, qty_available=180)
+        stock_2 = Stock.objects.create(product=product, short=False, qty_available=5100)
+        Stock.objects.create(product=product, short=False, qty_available=4000)
+        self.assertCountEqual(
+            Stock.objects.filter(short=Q(qty_available__lt=F('product__qty_target'))),
+            [stock_1, stock_2],
+        )
+        self.assertCountEqual(
+            Stock.objects.filter(short=ExpressionWrapper(
+                Q(qty_available__lt=F('product__qty_target')),
+                output_field=BooleanField(),
+            )),
+            [stock_1, stock_2],
+        )