[release/10.0] Fix ArgumentOutOfRangeException for entities with shadow properties and nullable complex types with discriminators

[Copilot]

Fixes #37337

Description

EF doesn't currently support shadow properties on complex types. However, the discriminator property is special-cased (it's used internally by EF to distinguish null vs empty complex properties). Unfortunately, there was a code path missed.

Customer impact

Applications that use a discriminator on a nullable complex property will fail at runtime when querying the affected entities. There is no good workaround for this.

How found

Customer reported on EF 10.0.0, this is a relatively common scenario for optional complex properties.

Regression

No, new feature in EF 10.

Testing

Test added.

Risk

Low. The fix is targeted and quirked.

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[AndriySvyryd]

@copilot Update progress by rewriting the PR summary using this template:

Fixes #{number}

**Description**
{Issue description}

**Customer impact**
{How does the reported issue affects customer's app? Are there workarounds?}

**How found**
{Was it customer reported or found during verification? How many customers are affected?}

**Regression**
{Is it a regression from a released version? Which one?}

**Testing**
{How the changes were tested}

**Risk**
{Low/Medium/High, argument why}

[Copilot]

Pull request overview

This PR fixes an ArgumentOutOfRangeException that occurs when querying entities that have both shadow properties and nullable complex types with discriminators (issue #37337). The fix ensures that shadow properties on complex types are replaced with default values during snapshot creation, since shadow property materialization on complex types is not currently supported in EF Core.

Key Changes:

• Added an AppContext switch Microsoft.EntityFrameworkCore.Issue37337 for backward compatibility control
• Modified SnapshotFactoryFactory.CreateSnapshotExpression to handle shadow properties on complex types by using default values instead of attempting materialization
• Added comprehensive test coverage to verify the fix works correctly

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 8 comments.

File	Description
src/EFCore/ChangeTracking/Internal/SnapshotFactoryFactory.cs	Implements the fix by detecting shadow properties on complex types and substituting them with default values during snapshot creation, controlled by an AppContext switch
test/EFCore.Specification.Tests/Query/AdHocComplexTypeQueryTestBase.cs	Adds a test that reproduces the scenario with shadow properties, nullable complex types with discriminators, and verifies the fix works correctly

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[artl93]

Customer reported, new feature, low risk. Approved.