[Copilot]

VSTHRD200 incorrectly treated IAsyncEnumerator<T> as a non-async return type, causing false "remove Async suffix" warnings and missing "add Async suffix" warnings for methods returning it.

Changes

• Utils.cs — Extended IsAsyncCompatibleReturnType to recognize IAsyncEnumerator<T> (in addition to IAsyncEnumerable<T>) as an async-compatible return type. Both live in System.Collections.Generic so the check is a simple name OR condition on the existing namespace check.
• VSTHRD200UseAsyncNamingConventionAnalyzerTests.cs — Added two test cases mirroring the existing IAsyncEnumerable<T> coverage: one confirming a warning is generated without the Async suffix, and one confirming no warning with the suffix.

// Before fix: no warning (should warn), and FooAsync would get a spurious "remove Async" warning
IAsyncEnumerator<int> Foo() => ...;

// After fix: VSTHRD200 correctly requires the Async suffix
IAsyncEnumerator<int> FooAsync() => ...;

[Copilot]

Pull request overview

This PR fixes the VSTHRD200 async naming analyzer so that methods returning IAsyncEnumerator<T> are treated as “async-focused” return types, eliminating incorrect “remove Async suffix” suggestions and restoring the expected “add Async suffix” diagnostic behavior.

Changes:

• Extend Utils.IsAsyncCompatibleReturnType to recognize System.Collections.Generic.IAsyncEnumerator<T> alongside IAsyncEnumerable<T>.
• Add VSTHRD200 test coverage to ensure methods returning IAsyncEnumerator<T> require the Async suffix and don’t warn when the suffix is present.

Reviewed changes

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

File	Description
src/Microsoft.VisualStudio.Threading.Analyzers/Utils.cs	Updates async-focused return type detection to include IAsyncEnumerator<T> by name under System.Collections.Generic.
test/Microsoft.VisualStudio.Threading.Analyzers.Tests/VSTHRD200UseAsyncNamingConventionAnalyzerTests.cs	Adds two new tests validating VSTHRD200 diagnostics for IAsyncEnumerator<T> return types (with and without Async suffix).