Annotate ServiceDescriptor.IsKeyedService for nullability flow and sync ref assembly

[Copilot]

ServiceDescriptor.ServiceKey is nullable (object?), so static analysis did not infer non-nullness after if (descriptor.IsKeyedService). This change makes that contract explicit so keyed-service branches no longer require null-forgiving operators.

• Nullability contract (implementation)

  • Added [MemberNotNullWhen(true, nameof(ServiceKey))] to ServiceDescriptor.IsKeyedService in Microsoft.Extensions.DependencyInjection.Abstractions.

• Nullability contract (reference assembly)

  • Added the matching [MemberNotNullWhen(true, "ServiceKey")] annotation to ServiceDescriptor.IsKeyedService in Microsoft.Extensions.DependencyInjection.Abstractions/ref to keep ref/src API annotations in sync.

if (descriptor.IsKeyedService)
{
    object serviceKey = descriptor.ServiceKey; // now recognized as non-null by flow analysis
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Static nullability analysis for ServiceDescriptor.ServiceKey does not take into account ServiceDescriptor.IsKeyedService</issue_title>
<issue_description>### Description

ServiceDescriptor.ServiceKey is typed as object? with nullable reference types enabled.
The static analyzer then cannot take into account the result of ServiceDescriptor.IsKeyedService and even if the service is known to be a keyed service, believes ServiceKey may still be null.
Even though IsKeyedService is implemented as

/// <summary>
/// Indicates whether the service is a keyed service.
/// </summary>
public bool IsKeyedService => ServiceKey != null;

Reproduction Steps

#nullable enable

public void Example(ServiceDescriptor descriptor)
{
  if (descriptor.IsKeyedService) {
    object serviceKey = descriptor.ServiceKey; // <-- complains about potential nullness
  }
}

Expected behavior

Would expect no complaints about potential nullness.

Actual behavior

Got complaints about nullness.

Regression?

No response

Known Workarounds

Use the 'null-forgiving' operator (!) to discard potential nullness. E.g.

#nullable enable

public void Example(ServiceDescriptor descriptor)
{
  if (descriptor.IsKeyedService) {
    object serviceKey = descriptor.ServiceKey!; // <-- no longer complains about potential nullness
  }
}

Configuration

.NET version: .NET 10

Other information

The problem lies in a missing [MemberNotNullWhen] annotation.
The following should fix it:

/// <summary>
/// Indicates whether the service is a keyed service.
/// </summary>
[MemberNotNullWhen(returnValue: true, nameof(ServiceKey)]
public bool IsKeyedService => ServiceKey != null;
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Static nullability analysis for ServiceDescriptor.ServiceKey does not take into account ServiceDescriptor.IsKeyedService #124465

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[Copilot]

Pull request overview

This PR addresses a nullability flow analysis issue by adding [MemberNotNullWhen(true, nameof(ServiceKey))] to ServiceDescriptor.IsKeyedService. This annotation tells the C# compiler that when IsKeyedService returns true, the ServiceKey property is guaranteed to be non-null, eliminating the need for null-forgiving operators (!) in code that checks this property.

Changes:

• Added [MemberNotNullWhen(true, nameof(ServiceKey))] attribute to ServiceDescriptor.IsKeyedService in the implementation
• Synced the annotation to the reference assembly
• Added regression test to verify the attribute is present and correctly configured

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceDescriptor.cs	Added MemberNotNullWhen attribute to IsKeyedService property to improve nullability flow analysis
src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs	Synced the MemberNotNullWhen attribute to the reference assembly
src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceCollectionKeyedServiceExtensionsTest.cs	Added reflection-based test to ensure the attribute is present with correct parameters

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[Copilot]

Pull request overview

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

[danmoseley]

/tmp/helix/working/B086093A/p/build/apple/AppleBuild.targets(260,5): error : LLVM ERROR: IO failure on output stream: No space left on device