[Bug]: NativeAOT / trimming warnings in Refit 11.0.1

[RoccoZero]

Describe the bug 🐞

Hi.

Can you please check and fix the NativeAOT / trimming warnings in Refit?

When publishing my project with NativeAOT enabled, I get many IL2026, IL2104, and IL3053 warnings from Refit and Refit.HttpClientFactory.

I would be very grateful if these warnings could be fixed or reduced, because my project targets NativeAOT and these warnings are very annoying/noisy during build.

The main warning comes from:

Refit.IRequestBuilder.BuildRestResultFuncForMethod(String, Type[], Type[])

It is marked with RequiresUnreferencedCodeAttribute, and the generated Refit implementation calls it, which produces many warnings.

Example warnings:

ILC : Trim analysis warning IL2026: Refit.Implementation.Generated.DivineClientRestIAuthRestApi.<SignIn>d__6.MoveNext(): Using member 'Refit.IRequestBuilder.BuildRestResultFuncForMethod(String,Type[],Type[])' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Refit uses reflection to analyze interface methods. Ensure referenced interfaces and DTOs are preserved when trimming.

Refit.HttpClientFactory.dll : warning IL2104: Assembly 'Refit.HttpClientFactory' produced trim warnings.

Refit.dll : warning IL2104: Assembly 'Refit' produced trim warnings.

Refit.dll : warning IL3053: Assembly 'Refit' produced AOT analysis warnings.

SystemTextJsonContentSerializer.cs: Trim analysis warning IL2026: JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext.

Step to reproduce

I am using:

• Refit: 11.0.1
• Refit.HttpClientFactory: 11.0.1
• Target framework: net10.0
• NativeAOT enabled

1. Create a .NET project that uses Refit.
2. Enable NativeAOT / trimming.
3. Add Refit interfaces and use source-generated Refit implementation.
4. Publish/build the project.
5. See NativeAOT / trimming warnings.

Reproduction repository

https://github.com/reactiveui/refit

Expected behavior

Refit should build cleanly with NativeAOT/trimming enabled, or provide an official NativeAOT-friendly way to avoid these warnings.

Ideally, source-generated Refit clients should not call APIs marked with RequiresUnreferencedCodeAttribute, such as:

Refit.IRequestBuilder.BuildRestResultFuncForMethod(String, Type[], Type[])

Also, JSON serialization should use JsonSerializerContext / JsonTypeInfo-based overloads where possible, so NativeAOT projects can avoid IL2026, IL2104, and IL3053 warnings.

Screenshots 🖼️

No response

IDE

Visual Studio 2022

Operating system

Windows 11

Version

No response

Device

No response

Refit Version

11.0.1

Additional information ℹ️

No response

[cschanhniem]

I investigated this. The root issue is structural, not just an annotation gap.

When the Refit source generator emits a method body (Emitter.cs WriteRefitMethod, ~line 271), it generates:

var ______func = requestBuilder.BuildRestResultFuncForMethod("{lookupName}", {parameterTypesExpression}{genericString});

This calls RequestBuilderImplementation.BuildRestResultFuncForMethod which is annotated [RequiresUnreferencedCode] and uses System.Linq.Expressions to build a compiled delegate at runtime — fundamentally incompatible with NativeAOT. The generated code has all the type information at compile time (parameter types, return type, method name), yet delegates to a runtime reflection path instead of generating the typed call directly.

The fix isn't adding [UnconditionalSuppressMessage] — it's making the source generator emit a method-specific typed delegate instead of the generic Func<HttpClient, object[], object?> path. The generator already knows:

• The interface method signature (return type, parameter types, parameter names)
• The RestMethodInfo (HTTP method, URL template, etc.)
• Whether it returns Task, Task<T>, IObservable<T>, ApiResponse<T>, etc.

A NativeAOT-compatible path would generate directly:

// Instead of:
var ______func = requestBuilder.BuildRestResultFuncForMethod("GetUser", ...);
return (UserInfo)(await ______func(Client, [id]).ConfigureAwait(false));

// Generate:
var request = requestBuilder.BuildRequestMessageForMethod("GetUser", 
    typeof(IGitHubApi).GetMethod(nameof(IGitHubApi.GetUser)), [id]);
using var response = await Client.SendAsync(request, cancellationToken);
// ... typed deserialization path inline

The BuildRequestMessageForMethod path (already in IRequestBuilder) doesn't carry [RequiresUnreferencedCode] — it's the expression-tree compilation in BuildRestResultFuncForMethod that blocks AOT. Generating the request+build pipeline inline in the source generator would eliminate all IL2026/IL2104/IL3053 warnings for generated clients.

The SystemTextJsonContentSerializer warning is separate and would require exposing JsonTypeInfo overloads through Refit's serialization pipeline, or allowing users to supply their own JsonSerializerContext via RefitSettings.

[glennawatson]

This is fixed on main for generated clients.

The source generator now emits request construction directly for supported methods instead of calling BuildRestResultFuncForMethod. That removes the main NativeAOT/trimming warning path reported here. We also added a NativeAOT smoke project that publishes with trimming/AOT warnings treated as errors.

The wider trim/AOT work for every fallback and serializer path remains tracked separately in #1389.

This will be included in a release in the next week or two.

[RoccoZero]

thanks