[release/10.0] Fix SetProperty discard lambda failing for nullable value type properties in ExecuteUpdate

[roji]

Fixes #37974
Backports #37975

Description
When using ExecuteUpdate with SetProperty to assign a constant or literal value to a nullable value type property (e.g. int?) via a discard lambda (_ => 1), EF Core throws InvalidOperationException: No coercion operator is defined between types Func<Entity, int?> and int. This was introduced by the EF Core 10 refactoring of ExecuteUpdate from Expression<Func<...>> to Func<...> for the setter parameter.

The root cause is in ExpressionTreeFuncletizer.ProcessEvaluatableRoot: when constantizing a value that needs a nullable conversion (e.g. int → int?), ConvertIfNeeded internally calls Visit, which corrupts the _state field back to EvaluatableWithoutCapturedVariable. This causes the parent VisitLambda to incorrectly treat the entire lambda as evaluatable, compiling it into a Func<Entity, int?> delegate. The downstream TranslateSetterValueSelector then receives a QueryParameterExpression instead of a LambdaExpression and throws.

Customer impact
Users calling ExecuteUpdateAsync with a constant/literal value assigned to a nullable value type property via a discard lambda get an InvalidOperationException at query compilation time. This is a common pattern:

const int SystemUserId = 1;
await ctx.Orders.ExecuteUpdateAsync(s =>
    s.SetProperty(p => p.UpdatedById, _ => SystemUserId)); // UpdatedById is int?, throws

Workarounds exist: cast the value to int? explicitly, or use a named parameter (p =>) instead of a discard (_ =>). Both workarounds are somewhat discoverable from the error message but unintuitive.

How found
User reported on EF Core 10.0.0. One additional user has also reported being affected. The issue has 2 reactions (+1 and eyes).

Regression
Yes, this is a regression from EF Core 9 to EF Core 10. It was introduced as a side effect of the ExecuteUpdate refactoring that changed the setter parameter from Expression<Func<...>> to Func<...> (the breaking change documented at https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-10.0/breaking-changes#execute-update-expression).

Testing
Added 1 new test (Update_Where_set_nullable_int_constant_via_discard_lambda) with SQL baseline assertions in both SQLite and SQL Server test classes.

Risk
Extremely low. The fix is a single-line state reset (state = State.NoEvaluatability) after ConvertIfNeeded returns, restoring the state that was already set earlier in the method but got corrupted by the internal Visit call. Quirk added (Microsoft.EntityFrameworkCore.Issue37974) to opt out.

[Copilot]

Pull request overview

Fixes an EF Core 10 regression where ExecuteUpdate/SetProperty using a discard lambda (_ => 1) fails when assigning a constant/literal to a nullable value type property (e.g. int?), by preventing ExpressionTreeFuncletizer state corruption during constantization and adding coverage for the scenario.

Changes:

• Reset funcletizer state after ConvertIfNeeded when constantizing an evaluatable root (with an AppContext quirk to opt out).
• Add a new bulk update test covering SetProperty(..., _ => 1) for a nullable int property in the Northwind spec tests.
• Add SQLite and SQL Server SQL baseline assertions for the new test.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/EFCore/Query/Internal/ExpressionTreeFuncletizer.cs	Resets state after ConvertIfNeeded to avoid _state corruption when constantizing, gated by an AppContext switch.
test/EFCore.Specification.Tests/BulkUpdates/NorthwindBulkUpdatesTestBase.cs	Adds provider-agnostic test for updating Product.SupplierID (int?) via discard-lambda constant setter.
test/EFCore.Sqlite.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqliteTest.cs	Adds SQLite SQL baseline for the new nullable-int discard-lambda update test.
test/EFCore.SqlServer.FunctionalTests/BulkUpdates/NorthwindBulkUpdatesSqlServerTest.cs	Adds SQL Server SQL baseline for the new nullable-int discard-lambda update test.

[artl93]

Approved. Regression. Customer reported.