NBJSONRPC001: Unsupported JSON-RPC proxy input

Property	Value
ID	NBJSONRPC001
Category	Usage
Default severity	Warning

The source generator reports this diagnostic when an interface annotated with JsonRpcContractAttribute or RpcMarshalableAttribute cannot be represented by the generated JSON-RPC proxy implementation. The reported location identifies the unsupported interface declaration, method, or event. Setting JsonRpcContractAttribute.GenerateProxy to false suppresses proxy generation and this diagnostic, but contract analysis remains active.

Why this is reported

The generator must emit a proxy whose signatures and wire behavior match the contract. It reports unsupported input rather than emitting an incomplete proxy. Current restrictions include non-partial, nested, and generic interfaces; properties and events on RPC-marshalable interfaces; static or generic methods; and methods with params, by-reference, ref-like, or pointer parameters. Proxy methods must return Task, Task<T>, ValueTask, ValueTask<T>, IAsyncEnumerable<T>, or void where notifications are allowed. Cancellation tokens must be the final parameter. RPC-marshalable interfaces must extend IDisposable unless they use call-scoped lifetime.

Proxy events must be instance events whose delegates return void and accept only by-value, non-ref-like parameters. Asynchronous, value-returning, static, and by-reference event contracts report this diagnostic. Event parameters also cannot contain RPC-marshalable interfaces, including within arrays or generic types, because notifications do not support marshaled handles.

Interface groups must contain non-null, non-generic, non-nested interface types with supported RPC members. On a marshalable contract, every group member must also be declared with RpcMarshalableOptionalInterfaceAttribute. Invalid groups report this diagnostic instead of emitting an incomplete proxy; see generated interface groups.

Examples

Unsupported:

[JsonRpcContract]
internal interface ICalculator
{
    Task<int> AddAsync(int left, int right);
}

Corrected:

[JsonRpcContract]
internal partial interface ICalculator
{
    Task<int> AddAsync(int left, int right);
}

For a method-signature diagnostic, remove the unsupported parameter or return shape, or change the contract to a supported asynchronous signature. The generator does not provide a code fix; adjust the contract according to the reported reason. Suppress the warning only when the unsupported declaration is intentionally not used to generate a proxy.