Open Generic Handlers

Header

• ID: analyzers.open-generic-handler-shape
• Diagnostic: LB1005 (Error)
• Maturity: GA
• Summary: Reports open generic handler definitions that expose an unsupported generic arity for bare message-type handler shapes.

Trigger Conditions

LB1005 reports when all of the following are true:

• Handler type is generic.
• Handler type uses a bare message type parameter in the first handler interface type argument.
• Open generic handler definition exposes type parameter count other than 1.

Diagnostic locations include:

• Type declaration location.
• typeof(...) registration location when unsupported handler is referenced in typeof expression.

Bad Example

using System.Threading;
using System.Threading.Tasks;
using LiteBus.Commands.Abstractions;

public sealed class InvalidLogger<TCommand, TContext> : ICommandPreHandler<TCommand>
    where TCommand : ICommand
{
    public Task PreHandleAsync(TCommand command, CancellationToken cancellationToken = default)
        => Task.CompletedTask;
}

Expected diagnostic:

• LB1005 with arity 2.

Good Example

using System.Threading;
using System.Threading.Tasks;
using LiteBus.Commands.Abstractions;

public sealed class CommandLogger<TCommand> : ICommandPreHandler<TCommand>
    where TCommand : ICommand
{
    public Task PreHandleAsync(TCommand command, CancellationToken cancellationToken = default)
        => Task.CompletedTask;
}

Suppression Guidance

• Refactor unsupported generic handler types to one message type parameter.
• Keep auxiliary generic context in constructor dependencies or closed helper services.
• Do not suppress unless compatibility with a fixed external generic contract is required.

Test Coverage

Source: tests/LiteBus.Analyzers.UnitTests/UnsupportedOpenGenericHandlerAnalyzerTests.cs