Generate a real async iterator for IAsyncEnumerable actions #13187

[yasmoradi]

Closes #13187.

An IAsyncEnumerable<T> action generated a proxy that did not compile (CS1622): an async method with the iterator's return type and a return statement, wrapped in prerenderStateService.GetValue — which stores one resolved value per url and cannot hold a stream.

The streamed path is now a real async iterator:

public async IAsyncEnumerable<string> PerformDiagnostic(..., [EnumeratorCancellation] CancellationToken cancellationToken)
{
    using var __request = new HttpRequestMessage(HttpMethod.Get, __url);
    ...
    using var __response = await httpClient.SendAsync(__request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
    await foreach (var __item in __response.Content.ReadFromJsonAsAsyncEnumerable(options.GetTypeInfo<string>(), cancellationToken))
    {
        yield return __item;
    }
}

• yields the items through instead of returning them
• skips the prerender state for this shape only
• [EnumeratorCancellation] on the token, so a WithCancellation at the call site reaches the enumerator
• the response's using moves inside the iterator, which makes WrapWithResponseDisposal redundant — removed
• the JsonTypeInfo is still passed, so trimming and AOT are unaffected

Every other action is generated exactly as before.

Verified by building the generator and pointing Boilerplate.Shared at it in place of the package, with IDiagnosticController.PerformDiagnostic declared as IAsyncEnumerable<string>: the project builds, the emitted method is the one above, and the other 62 generated methods still go through prerenderStateService unchanged.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved generated HTTP client proxies for streaming responses returned as asynchronous streams.
  • Streamed items are now delivered incrementally without unnecessary response wrapping.
  • Cancellation requests are now correctly propagated while consuming asynchronous streams.
  • Streaming responses remain available for the duration of enumeration, preventing premature disposal.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Advanced

Run ID: d4832af7-eea3-4423-9b78-282ef36a4e36

📥 Commits

Reviewing files that changed from the base of the PR and between 7b52dbe and 6d25edb.

📒 Files selected for processing (1)

• src/SourceGenerators/Bit.SourceGenerators/HttpClientProxy/HttpClientProxySourceGenerator.cs

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Walkthrough

The source generator now identifies direct IAsyncEnumerable<T> methods separately from task-wrapped streams. It generates iterator-compatible proxy methods with enumerator cancellation and stream-owned response disposal.

Changes

Async stream proxy generation

Layer / File(s)	Summary
Async stream classification and encoding src/SourceGenerators/Bit.SourceGenerators/HttpClientProxy/HttpClientProxySourceGenerator.cs	The generator records whether an action directly returns IAsyncEnumerable<T>. It encodes and parses the new action field.
Async stream method generation src/SourceGenerators/Bit.SourceGenerators/HttpClientProxy/HttpClientProxySourceGenerator.cs	Direct async streams receive [EnumeratorCancellation], use await foreach, skip prerender-state wrapping, and keep the response undisposed while the stream is consumed.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 6d25e

Direct IAsyncEnumerable proxy actions now compile and stream response items while keeping the response alive through enumeration. No concrete merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the primary change: generating a real async iterator for direct IAsyncEnumerable actions. It directly matches issue #13187.
Linked Issues check	✅ Passed	The changes address issue #13187 by generating a valid async iterator for direct IAsyncEnumerable returns, using streaming response handling, applying EnumeratorCancellation, preserving response li…
Out of Scope Changes check	✅ Passed	The changes are limited to the HttpClientProxy source generator behavior required for direct IAsyncEnumerable actions. No unrelated code changes are identified.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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