How to handle "Enable generated request building for this method" error

[wokket]

There's a good chance I've just missed something obvious in the docs here...

I'm experimenting with the new reflection-free code paths, and have swapped out AddRefitClient for AddRefitGeneratedClient, but I get the fallback error at runtime "This Refit client was created with the generated-only API, but the generated client needs the reflection request builder for 'MethodName'. Enable generated request building for this method or use RestService.For when reflection is acceptable.".

So how to do I enable generated request building? There's docs around disabling various source-gen things, but I'm clearly missing diagnostics/info on a. why the code gen has failed/fallen back for this method, and b. how to correct that...

[yudin-s]

That message means the generated client exists, but that particular method did not get the new direct generated-request-building path.

AddRefitGeneratedClient<T>() is the strict/native-AOT path. It uses RestService.ForGenerated<T>() and deliberately does not register the old reflection IRequestBuilder<T> fallback. So if one interface method is generated as "call the reflection request builder for this method", resolving/calling it fails with that message.

The confusing part is the word "enable". There is no per-method runtime switch to call in DI. In the current README, generated request building is on by default, and the project property shown is the opposite switch:

<PropertyGroup>
  <RefitGeneratedRequestBuilding>false</RefitGeneratedRequestBuilding>
</PropertyGroup>

Setting that to false keeps source-generated client types but makes methods use the legacy reflective request-building path, which is not compatible with AddRefitGeneratedClient<T>().

I would debug it like this:

1. Make sure the app project references Refit with PackageReference, because the source generator comes from the main package.
2. Temporarily emit generated files:

<PropertyGroup>
  <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
  <CompilerGeneratedFilesOutputPath>Generated</CompilerGeneratedFilesOutputPath>
</PropertyGroup>

3. Inspect the generated implementation for the failing interface method. If that method still routes through BuildRestResultFuncForMethod / reflection-style request building, its signature uses a shape the direct request builder cannot currently emit.
4. Compare that method against the supported list in the README's "Generated request building" section. Common safe shapes include static/dynamic headers, header collections, body content, properties, cancellation tokens, and the usual Task / Task<T> / ApiResponse<T> returns.

So the practical choices are:

• If reflection is acceptable, use AddRefitClient<T>() instead of AddRefitGeneratedClient<T>().
• If you need native-AOT/generated-only behavior, simplify or isolate the unsupported method shape, then check the generated file again.
• If the method looks like it should be covered by the README's supported list, open an issue with the interface method signature and the generated method body, because that would likely be a generator coverage gap.

Relevant source/docs:

• README sections "Generated-only client registration with IHttpClientFactory" and "Generated request building": https://github.com/reactiveui/refit/blob/main/README.md#generated-only-client-registration-with-ihttpclientfactory
• AddRefitGeneratedClient<T>() registration code: https://github.com/reactiveui/refit/blob/main/src/Refit.HttpClientFactory/HttpClientFactoryExtensions.ServiceCollection.cs
• Core registration calling RestService.ForGenerated<T>(): https://github.com/reactiveui/refit/blob/main/src/Refit.HttpClientFactory/HttpClientFactoryCore.cs

If this explains the error path, please mark it as answered.

[glennawatson]

Yeah, there's some work tracked in a recent issue for me to do to add some analyzers to detect issues at compile time around registrations that can't use the AOT friendly route in the source generator. I'm hoping to get that out this week. Plus another community member has actively been contributing towards more generation scenarios.

[wokket]

Thanks for the info guys, I've been able to repro the issue so will take it over there. I'm loving the work on reduced overheads/better perf, thanks heaps 🍻