FromServiceKeyAttribute to support nullable (for unkeyed) and to use current service key

[steveharter]

Fixes #113585

(draft to verify tests)

This is API approved except for this which is being done via email:

public static object FromServiceKey { get; }

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[Copilot]

Pull Request Overview

This PR updates the handling of keyed services to support nullable (unkeyed) services and to use the current service key by distinguishing between lookup modes.

• Refactored CallSiteFactory logic to separate InheritKey and ExplicitKey scenarios.
• Updated FromKeyedServicesAttribute to set LookupMode based on whether the provided key is null.
• Added tests for resolving both keyed and unkeyed services.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs	Updated keyed resolution logic to handle InheritKey and ExplicitKey modes.
src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/KeyedDependencyInjectionSpecificationTests.cs	Added tests for resolving services under various key scenarios, including unkeyed services.
src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ServiceKeyLookupMode.cs	Introduced ServiceKeyLookupMode with three possible modes.
src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/FromKeyedServicesAttribute.cs	Modified attribute constructor to set LookupMode appropriately.
src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs	Updated public API reference to reflect the changes in the attribute constructors and enum.

[ericstj]

I applied the API review feedback from #113585 (comment). @stephentoub @halter73 can you please have a review?

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

1. Create and link to this PR and the issue a matching issue in the dotnet/docs repo using the breaking change documentation template, then remove this needs-breaking-change-doc-created label.
2. Ask a committer to mail the .NET Breaking Change Notification DL.

Tagging @dotnet/compat for awareness of the breaking change.

[ericstj]

📋 Breaking Change Documentation Required

Create a breaking change issue with AI-generated content

Generated by Breaking Change Documentation Tool - 2025-10-03 13:47:42

[stephentoub]

@ericstj, it's not clear to me what the breaking change here is we want to document... just that a property which could have always returned null but was annotated to say it couldn't is now annotated to say that it can?

[ericstj]

Nevermind, looks like I already documented this one in dotnet/docs#46269 but linked to the issue and not the PR.