[Bug]: AddRefitGeneratedClient fails for methods with query parameters

[RoccoZero]

Describe the bug 🐞

AddRefitGeneratedClient<T>() throws NotSupportedException at runtime when a generated Refit method contains query parameters.

Minimal interface:

public interface IAuthRestApi
{
    [Get("/signin")]
    Task<JsonNode> SignIn(
        [AliasAs("login")] string login,
        [AliasAs("password")] string password);
}

Registration:

[JsonSerializable(typeof(JsonNode))]
public partial class ApiJsonSerializerContext : JsonSerializerContext
{
}

var settings = new RefitSettings
{
    ContentSerializer = new SystemTextJsonContentSerializer(
        ApiJsonSerializerContext.Default.Options)
};

services
    .AddRefitGeneratedClient<IAuthRestApi>(settings)
    .ConfigureHttpClient(client =>
        client.BaseAddress = new Uri("https://api.example.com"));

Calling:

await api.SignIn("login", "password");

throws:

System.NotSupportedException: This Refit client was created with the generated-only API, but the generated client needs the reflection request builder for 'SignIn'. Enable generated request building for this method or use RestService.For when reflection is acceptable.
   at Refit.GeneratedOnlyRequestBuilder.BuildRestResultFuncForMethod(...)
   at Refit.Implementation.Generated.IAuthRestApi.SignIn(...)

The source generator creates IAuthRestApi.g.cs, but the generated SignIn implementation still uses the reflection-based path:

var refitFunc = refitRequestBuilder.BuildRestResultFuncForMethod(
    "SignIn",
    parameterTypes);

The same problem occurs when query parameters are explicitly included in the route:

[Get("/signin?login={login}&password={password}")]
Task<JsonNode> SignIn(string login, string password);

RefitGeneratedRequestBuilding is true, DisableRefitSourceGenerator is not enabled, and source-generated System.Text.Json metadata is provided for JsonNode.

A parameterless method returning the same JsonNode type is generated correctly through GeneratedRequestRunner.SendAsync, so the problem does not appear to be caused by JsonNode or JSON serialization. Other methods containing ordinary query parameters also fall back to BuildRestResultFuncForMethod.

Expected behavior: the source generator should generate request construction for ordinary route and query parameters so the interface can be used through AddRefitGeneratedClient<T>() in NativeAOT applications without reflection. If this method shape is intentionally unsupported, the analyzer should report a compile-time diagnostic explaining that the method is incompatible with generated-only registration instead of allowing registration and failing only at runtime.

Tested with:

• Refit 12.1.0
• Refit.HttpClientFactory 12.1.0
• .NET 10
• NativeAOT

Step to reproduce

Step to reproduce: See the complete reproduction steps in the bug description above.

Reproduction repository

https://github.com/reactiveui/refit

Expected behavior

See the expected behavior in the bug description above.

Screenshots 🖼️

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IDE

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Operating system

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Version

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Device

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Refit Version

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Additional information ℹ️

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[glennawatson]

Thanks for the report.

Two fold fix.

• feat: add generated request building support for path parameters in the URL. #2174 and potentially some changes after will allow support for some of these scenarios source generated.
• A analyzer like you suggested to report when that option isn't available. Started adding one now and will have a PR today.

[RoccoZero]

Update: I tested this again with Refit 13.1.0 and found that explicit query placeholders now work correctly:

[Get("/signin?login={login}&password={password}")]
Task<JsonNode> SignIn(string login, string password);

However, the equivalent method using Refit's automatic query-parameter behavior still does not work with AddRefitGeneratedClient<T>():

[Get("/signin")]
Task<JsonNode> SignIn2(string login, string password);

Calling SignIn2 throws NotSupportedException because the generated implementation still falls back to BuildRestResultFuncForMethod.

Therefore, the issue in Refit 13.1.0 appears to be specifically related to automatic query-string generation for method parameters. Explicit query placeholders are generated correctly, while implicit query parameters still require the reflection request builder.

[glennawatson]

Thanks for the update.

Yeah explicitly haven't gotten around to this issue yet, it's on the plan in the next week or so.