Fix to #23617 - IQueryable.All evaluate to false with predicate _ => …

…true

We have optimization for EXISTS, that returns false when the subquery has a predicate which filters out all the rows. In such case we return constant false. However, ExistExpression also stores information about it being negated or not (i.e. EXISTS vs NOT EXISTS).
If the Exists expression is negated and the predicate filters out all the rows we should return true instead.

src/EFCore.Relational/Query/SqlNullabilityProcessor.cs

@@ -551,10 +551,18 @@ protected virtual SqlExpression VisitExists(
             var subquery = Visit(existsExpression.Subquery);
             nullable = false;
 
+            if (AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore23617", out var enabled) && enabled)
+            {
+                return TryGetBoolConstantValue(subquery.Predicate) == false
+                    ? subquery.Predicate
+                    : existsExpression.Update(subquery);
+            }
+
             // if subquery has predicate which evaluates to false, we can simply return false
+            // if the exisits is negated we need to return true instead
             return TryGetBoolConstantValue(subquery.Predicate) == false
-                ? subquery.Predicate
-                : existsExpression.Update(subquery);
+                ? _sqlExpressionFactory.Constant(existsExpression.IsNegated, existsExpression.TypeMapping)
+                : (SqlExpression)existsExpression.Update(subquery);
         }
 
         /// <summary>

test/EFCore.Specification.Tests/Query/NorthwindAggregateOperatorsQueryTestBase.cs

@@ -1986,5 +1986,15 @@ public virtual Task Min_after_default_if_empty_does_not_throw(bool isAsync)
                 isAsync,
                 ss => ss.Set<Order>().Where(o => o.OrderID == 10243).Select(o => o.OrderID).DefaultIfEmpty());
         }
+
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual Task All_true(bool async)
+        {
+            return AssertAll(
+                async,
+                ss => ss.Set<Customer>(),
+                predicate: x => true);
+        }
     }
 }

test/EFCore.SqlServer.FunctionalTests/Query/NorthwindAggregateOperatorsQuerySqlServerTest.cs

@@ -1466,6 +1466,14 @@ public override async Task Count_on_projection_with_client_eval(bool async)
 FROM [Orders] AS [o]");
         }
 
+        public override async Task All_true(bool async)
+        {
+            await base.All_true(async);
+
+            AssertSql(
+                @"SELECT CAST(1 AS bit)");
+        }
+
         private void AssertSql(params string[] expected)
             => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);