[release/10.0] Fix ComplexProperty treated as nullable after update from EF Core 9.0 to 10.0

[Copilot]

Fixes #38043

Description

Upgrading from EF Core 9.0 to 10.0 with complex properties causes false PendingModelChangesWarning during MigrateAsync and spurious migrations.

The previous fix (#37690) for this included a guard that was incorrect and the fix didn't apply for most snapshots.

Customer impact

When upgrading from EF Core 9.x to 10.0 with complex properties:

• MigrateAsync() throws PendingModelChangesWarning at startup, blocking the application
• dotnet ef migrations add generates spurious AlterColumn with oldNullable: true

Workaround: suppress RelationalEventId.PendingModelChangesWarning via ConfigureWarnings, or generate and revert the spurious migration to update the snapshot model. The workaround is discoverable from the exception message.

How found

Customer reported on EF 10.0.5.

Regression

Yes, regression from EF Core 10.0.0 when optional complex property support was added. The first fix attempt (PR #37690, commit c214374) was incomplete.

Testing

Added unit test

Risk

Very low. The fix removes an incorrect condition from a guard clause — a one-line change in design-time code.

[AndriySvyryd]

@copilot Update progress using the servicing template

[Copilot]

@copilot Update progress using the servicing template

Updated the PR description with the servicing template format, including Description, Customer impact, How found, Regression, Testing, and Risk sections.

[Copilot]

Pull request overview

This PR adjusts EF Core design-time snapshot processing to ensure complex properties from EF Core 8.x/9.x snapshots are treated as non-nullable when loaded in EF Core 10.0, addressing false model-diff detection caused by property-bag complex types using Dictionary<string, object> as the snapshot CLR type.

Changes:

• Removed the !complexProperty.ClrType.IsNullableType() guard so the pre-10 snapshot fix applies to property-bag complex properties.
• Added a regression test covering property-bag complex property nullability update through SnapshotModelProcessor.

Reviewed changes

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

File	Description
src/EFCore.Design/Migrations/Internal/SnapshotModelProcessor.cs	Broadens the pre-10 snapshot nullability fix to apply regardless of complex property CLR type.
test/EFCore.Design.Tests/Migrations/Design/SnapshotModelProcessorTest.cs	Adds coverage for property-bag complex property nullability fixup when processing 9.x snapshots.

[AndriySvyryd]

@artl93