Fixed #31183 -- Added a feature flag for "<db> only supports UNBOUNDED together with PRECEDING and FOLLOWING".

django/db/backends/base/features.py

@@ -246,6 +246,7 @@ class BaseDatabaseFeatures:
     # Does the backend support window expressions (expression OVER (...))?
     supports_over_clause = False
     supports_frame_range_fixed_distance = False
+    only_supports_unbounded_with_preceding_and_following = False
 
     # Does the backend support CAST with precision?
     supports_cast_with_precision = True

django/db/backends/base/operations.py

@@ -658,7 +658,16 @@ class BaseDatabaseOperations:
         return self.window_frame_start(start), self.window_frame_end(end)
 
     def window_frame_range_start_end(self, start=None, end=None):
-        return self.window_frame_rows_start_end(start, end)
+        start_, end_ = self.window_frame_rows_start_end(start, end)
+        if (
+            self.connection.features.only_supports_unbounded_with_preceding_and_following and
+            ((start and start < 0) or (end and end > 0))
+        ):
+            raise NotSupportedError(
+                '%s only supports UNBOUNDED together with PRECEDING and '
+                'FOLLOWING.' % self.connection.display_name
+            )
+        return start_, end_
 
     def explain_query_prefix(self, format=None, **options):
         if not self.connection.features.supports_explaining_query_execution:

django/db/backends/postgresql/features.py

@@ -52,6 +52,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     $$ LANGUAGE plpgsql;"""
     requires_casted_case_in_updates = True
     supports_over_clause = True
+    only_supports_unbounded_with_preceding_and_following = True
     supports_aggregate_filter_clause = True
     supported_explain_formats = {'JSON', 'TEXT', 'XML', 'YAML'}
     validates_explain_options = False  # A query will error on invalid options.

django/db/backends/postgresql/operations.py

@@ -1,7 +1,6 @@
 from psycopg2.extras import Inet
 
 from django.conf import settings
-from django.db import NotSupportedError
 from django.db.backends.base.operations import BaseDatabaseOperations
 
 
@@ -275,15 +274,6 @@ class DatabaseOperations(BaseDatabaseOperations):
             return "(interval '1 day' * (%s - %s))" % (lhs_sql, rhs_sql), params
         return super().subtract_temporals(internal_type, lhs, rhs)
 
-    def window_frame_range_start_end(self, start=None, end=None):
-        start_, end_ = super().window_frame_range_start_end(start, end)
-        if (start and start < 0) or (end and end > 0):
-            raise NotSupportedError(
-                'PostgreSQL only supports UNBOUNDED together with PRECEDING '
-                'and FOLLOWING.'
-            )
-        return start_, end_
-
     def explain_query_prefix(self, format=None, **options):
         prefix = super().explain_query_prefix(format)
         extra = {}

tests/expressions_window/tests.py

@@ -1,5 +1,5 @@
 import datetime
-from unittest import mock, skipIf, skipUnless
+from unittest import mock, skipIf
 
 from django.core.exceptions import FieldError
 from django.db import NotSupportedError, connection
@@ -750,9 +750,9 @@ class WindowFunctionTests(TestCase):
                 frame=RowRange(end='a'),
             )))
 
-    @skipUnless(connection.vendor == 'postgresql', 'Frame construction not allowed on PostgreSQL')
+    @skipUnlessDBFeature('only_supports_unbounded_with_preceding_and_following')
-    def test_postgresql_illegal_range_frame_start(self):
+    def test_unsupported_range_frame_start(self):
-        msg = 'PostgreSQL only supports UNBOUNDED together with PRECEDING and FOLLOWING.'
+        msg = '%s only supports UNBOUNDED together with PRECEDING and FOLLOWING.' % connection.display_name
         with self.assertRaisesMessage(NotSupportedError, msg):
             list(Employee.objects.annotate(test=Window(
                 expression=Sum('salary'),
@@ -760,9 +760,9 @@ class WindowFunctionTests(TestCase):
                 frame=ValueRange(start=-1),
             )))
 
-    @skipUnless(connection.vendor == 'postgresql', 'Frame construction not allowed on PostgreSQL')
+    @skipUnlessDBFeature('only_supports_unbounded_with_preceding_and_following')
-    def test_postgresql_illegal_range_frame_end(self):
+    def test_unsupported_range_frame_end(self):
-        msg = 'PostgreSQL only supports UNBOUNDED together with PRECEDING and FOLLOWING.'
+        msg = '%s only supports UNBOUNDED together with PRECEDING and FOLLOWING.' % connection.display_name
         with self.assertRaisesMessage(NotSupportedError, msg):
             list(Employee.objects.annotate(test=Window(
                 expression=Sum('salary'),