NBJSONRPC003: Unsupported contract member

Property	Value
ID	`NBJSONRPC003`
Category	Usage
Default severity	Warning

An RPC contract contains an unsupported member. Abstract properties and indexers cannot be invoked through the RPC protocol; use asynchronous methods instead. Default interface property implementations are allowed because they execute locally.

When JsonRpcContractAttribute.GenerateProxy is false, this rule also validates method signatures and event delegates. When generating a proxy, the source generator reports these signature and event restrictions as NBJSONRPC001, avoiding duplicate diagnostics. Supported methods return Task, Task<T>, ValueTask, ValueTask<T>, IAsyncEnumerable<T>, or void for notifications. RPC methods must not be static or generic, and parameters must not be params, by-reference, ref-like, or pointers. Concrete static interface helpers are excluded from proxy generation and contract analysis; static abstract methods remain unsupported. Cancellation tokens must appear last. Notifications cannot carry RPC-marshalable interfaces. Events must be instance events with synchronous, void-returning delegates and supported by-value parameters. Marshalable interfaces cannot declare events.

Inherited members are included. These checks require JsonRpcContractAttribute or RpcMarshalableAttribute.

Example

Unsupported:

[JsonRpcContract(GenerateProxy = false)]
public interface IUnsupportedCounter
{
    int Count { get; }
}

Corrected:

[JsonRpcContract(GenerateProxy = false)]
[GenerateShape(IncludeMethods = MethodShapeFlags.PublicInstance)]
public partial interface ICounter
{
    ValueTask<int> GetCountAsync(CancellationToken cancellationToken);
}

No automatic code fix is offered. Change the contract to supported RPC members; suppress the diagnostic only when the member is intentionally not part of the RPC surface.

Table of Contents

NBJSONRPC003: Unsupported contract member

Example