Fix on top of Copilot's work.

Author: cincuranet

src/EFCore/Query/Internal/NullCheckRemovingExpressionVisitor.cs

@@ -24,8 +24,8 @@ protected override Expression VisitBinary(BinaryExpression binaryExpression)
     {
         var visitedExpression = base.VisitBinary(binaryExpression);
 
-        return TryOptimizeQueryableNullCheck(visitedExpression)
-            ?? TryOptimizeConditionalEquality(visitedExpression)
+        return TryOptimizeConditionalEquality(visitedExpression)
+            ?? TryOptimizeQueryableNullCheck(visitedExpression)
             ?? visitedExpression;
     }
 
@@ -77,34 +77,6 @@ protected override Expression VisitConditional(ConditionalExpression conditional
         return base.VisitConditional(conditionalExpression);
     }
 
-    private static Expression? TryOptimizeQueryableNullCheck(Expression expression)
-    {
-        // Optimize IQueryable/DbSet null checks
-        // IQueryable != null => true
-        // IQueryable == null => false
-        if (expression is BinaryExpression
-            {
-                NodeType: ExpressionType.Equal or ExpressionType.NotEqual
-            } binaryExpression)
-        {
-            var isLeftNull = IsNullConstant(binaryExpression.Left);
-            var isRightNull = IsNullConstant(binaryExpression.Right);
-
-            if (isLeftNull != isRightNull)
-            {
-                var nonNullExpression = isLeftNull ? binaryExpression.Right : binaryExpression.Left;
-
-                if (IsQueryableType(nonNullExpression.Type))
-                {
-                    var result = binaryExpression.NodeType == ExpressionType.NotEqual;
-                    return Expression.Constant(result, typeof(bool));
-                }
-            }
-        }
-
-        return null;
-    }
-
     private static Expression? TryOptimizeConditionalEquality(Expression expression)
     {
         // Simplify (a ? b : null) == null => !a || b == null
@@ -145,6 +117,34 @@ protected override Expression VisitConditional(ConditionalExpression conditional
         return null;
     }
 
+    private static Expression? TryOptimizeQueryableNullCheck(Expression expression)
+    {
+        // Optimize IQueryable/DbSet null checks:
+        // * IQueryable != null => true
+        // * IQueryable == null => false
+        if (expression is BinaryExpression
+            {
+                NodeType: ExpressionType.Equal or ExpressionType.NotEqual
+            } binaryExpression)
+        {
+            var isLeftNull = IsNullConstant(binaryExpression.Left);
+            var isRightNull = IsNullConstant(binaryExpression.Right);
+
+            if (isLeftNull != isRightNull)
+            {
+                var nonNullExpression = isLeftNull ? binaryExpression.Right : binaryExpression.Left;
+
+                if (nonNullExpression.Type.IsAssignableTo(typeof(IQueryable)))
+                {
+                    var result = binaryExpression.NodeType == ExpressionType.NotEqual;
+                    return Expression.Constant(result);
+                }
+            }
+        }
+
+        return null;
+    }
+
     private sealed class NullSafeAccessVerifyingExpressionVisitor : ExpressionVisitor
     {
         private readonly ISet<Expression> _nullSafeAccesses = new HashSet<Expression>(ExpressionEqualityComparer.Instance);
@@ -191,17 +191,4 @@ protected override Expression VisitUnary(UnaryExpression unaryExpression)
 
     private static bool IsNullConstant(Expression expression)
         => expression is ConstantExpression { Value: null };
-
-    private static bool IsQueryableType(Type type)
-    {
-        if (type.IsGenericType)
-        {
-            var genericTypeDefinition = type.GetGenericTypeDefinition();
-            return genericTypeDefinition == typeof(IQueryable<>)
-                || genericTypeDefinition == typeof(IOrderedQueryable<>)
-                || genericTypeDefinition == typeof(DbSet<>);
-        }
-
-        return type == typeof(IQueryable);
-    }
 }

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

@@ -1463,6 +1463,27 @@ public virtual Task Where_Queryable_ToArray_Length_member(bool async)
             assertOrder: true,
             elementAsserter: (e, a) => AssertCollection(e, a));
 
+    [ConditionalTheory, MemberData(nameof(IsAsyncData))]
+    public virtual Task Where_Queryable_not_null_check_with_Contains(bool async)
+        => AssertQuery(
+            async,
+            ss =>
+            {
+                var ids = ss.Set<Customer>().Select(c => c.CustomerID);
+                return ss.Set<Customer>().Where(c => ids != null && ids.Contains(c.CustomerID));
+            });
+
+    [ConditionalTheory, MemberData(nameof(IsAsyncData))]
+    public virtual Task Where_Queryable_null_check_with_Contains(bool async)
+        => AssertQuery(
+            async,
+            ss =>
+            {
+                var ids = ss.Set<Customer>().Select(c => c.CustomerID);
+                return ss.Set<Customer>().Where(c => ids == null || !ids.Contains(c.CustomerID));
+            },
+            assertEmpty: true);
+
     [ConditionalTheory, MemberData(nameof(IsAsyncData))]
     public virtual Task Where_collection_navigation_ToList_Count(bool async)
         => AssertQuery(

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

@@ -1890,6 +1890,36 @@ ORDER BY [c].[CustomerID]
 """);
     }
 
+    public override async Task Where_Queryable_not_null_check_with_Contains(bool async)
+    {
+        await base.Where_Queryable_not_null_check_with_Contains(async);
+
+        AssertSql(
+            """
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] IN (
+    SELECT [c0].[CustomerID]
+    FROM [Customers] AS [c0]
+)
+""");
+    }
+
+    public override async Task Where_Queryable_null_check_with_Contains(bool async)
+    {
+        await base.Where_Queryable_null_check_with_Contains(async);
+
+        AssertSql(
+            """
+SELECT [c].[CustomerID], [c].[Address], [c].[City], [c].[CompanyName], [c].[ContactName], [c].[ContactTitle], [c].[Country], [c].[Fax], [c].[Phone], [c].[PostalCode], [c].[Region]
+FROM [Customers] AS [c]
+WHERE [c].[CustomerID] NOT IN (
+    SELECT [c0].[CustomerID]
+    FROM [Customers] AS [c0]
+)
+""");
+    }
+
     public override async Task Where_collection_navigation_ToList_Count(bool async)
     {
         await base.Where_collection_navigation_ToList_Count(async);