Fix nullable value type coercion in ExpressionTreeFuncletizer.ProcessEvaluatableRoot

Co-authored-by: roji <1862641+roji@users.noreply.github.com>
Agent-Logs-Url: https://github.com/dotnet/efcore/sessions/1452f6d8-60ff-43d5-9380-319e917be42b

Author: Copilot

src/EFCore/Query/Internal/ExpressionTreeFuncletizer.cs

@@ -2006,10 +2006,15 @@ private static StateType CombineStateTypes(StateType stateType1, StateType state
             return evaluatableRoot;
         }
 
-        return ConvertIfNeeded(
+        var constantExpression = ConvertIfNeeded(
             Constant(value, value is null ? evaluatableRoot.Type : value.GetType()),
             evaluatableRoot.Type);
 
+        // ConvertIfNeeded calls Visit which may have modified _state; reset it since we've already evaluated this root as a constant.
+        state = State.NoEvaluatability;
+
+        return constantExpression;
+
         bool TryHandleNonEvaluatableAsRoot(Expression root, State state, bool asParameter, [NotNullWhen(true)] out Expression? result)
         {
             switch (root)

test/EFCore.Specification.Tests/BulkUpdates/NorthwindBulkUpdatesTestBase.cs

@@ -392,6 +392,16 @@ public virtual Task Update_Where_set_constant_via_lambda(bool async)
             rowsAffectedCount: 8,
             (b, a) => Assert.All(a, c => Assert.Equal("Updated", c.ContactName)));
 
+    [ConditionalTheory, MemberData(nameof(IsAsyncData))]
+    public virtual Task Update_Where_set_nullable_int_constant_via_discard_lambda(bool async)
+        => AssertUpdate(
+            async,
+            ss => ss.Set<Product>().Where(p => p.ProductID < 5),
+            e => e,
+            s => s.SetProperty(c => c.SupplierID, _ => 1),
+            rowsAffectedCount: 4,
+            (b, a) => Assert.All(a, p => Assert.Equal(1, p.SupplierID)));
+
     [ConditionalTheory, MemberData(nameof(IsAsyncData))]
     public virtual async Task Update_Where_parameter_set_constant(bool async)
     {

test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqlServerTest.cs

@@ -688,6 +688,19 @@ WHERE [c].[CustomerID] LIKE N'F%'
 """);
     }
 
+    public override async Task Update_Where_set_nullable_int_constant_via_discard_lambda(bool async)
+    {
+        await base.Update_Where_set_nullable_int_constant_via_discard_lambda(async);
+
+        AssertExecuteUpdateSql(
+            """
+UPDATE [p]
+SET [p].[SupplierID] = 1
+FROM [Products] AS [p]
+WHERE [p].[ProductID] < 5
+""");
+    }
+
     public override async Task Update_Where_parameter_set_constant(bool async)
     {
         await base.Update_Where_parameter_set_constant(async);

test/EFCore.Sqlite.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqliteTest.cs

@@ -667,6 +667,18 @@ public override async Task Update_Where_set_constant_via_lambda(bool async)
 """);
     }
 
+    public override async Task Update_Where_set_nullable_int_constant_via_discard_lambda(bool async)
+    {
+        await base.Update_Where_set_nullable_int_constant_via_discard_lambda(async);
+
+        AssertExecuteUpdateSql(
+            """
+UPDATE "Products" AS "p"
+SET "SupplierID" = 1
+WHERE "p"."ProductID" < 5
+""");
+    }
+
     public override async Task Update_Where_parameter_set_constant(bool async)
     {
         await base.Update_Where_parameter_set_constant(async);