Handler Coverage

Header

• ID: analyzers.missing-command-handler, analyzers.missing-query-handler
• Diagnostics: LB1008 (Error), LB1009 (Error)
• Maturity: GA
• Summary: Reports command, query, and stream query message types that do not have a main handler in the analyzed compilation and eligible referenced assemblies.

Trigger Conditions

LB1008 (Missing Command Handler)

The analyzer reports when a concrete ICommand or ICommand<TResult> type has no covering main command handler:

• No ICommandHandler<TCommand> or ICommandHandler<TCommand, TResult> for the type.
• No handler registered for a base command type that is assignable from the concrete type.
• No supported open generic main command handler that closes for the type.

LB1009 (Missing Query Handler)

The analyzer reports when a concrete query type has no matching main query handler:

• IQuery<TResult> requires IQueryHandler<TQuery, TResult>.
• IStreamQuery<TResult> requires IStreamQueryHandler<TQuery, TResult>.
• Stream queries are checked against stream query handlers, not regular query handlers.

Bad Example

using LiteBus.Commands.Abstractions;
using LiteBus.Queries.Abstractions;

public sealed record CreateUserCommand(string Name) : ICommand;
public sealed record GetUserQuery(int UserId) : IQuery<string>;

Expected diagnostics:

• LB1008 on CreateUserCommand
• LB1009 on GetUserQuery

Good Example

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

public sealed record CreateUserCommand(string Name) : ICommand;
public sealed record GetUserQuery(int UserId) : IQuery<string>;

public sealed class CreateUserCommandHandler : ICommandHandler<CreateUserCommand>
{
    public Task HandleAsync(CreateUserCommand command, CancellationToken cancellationToken = default)
        => Task.CompletedTask;
}

public sealed class GetUserQueryHandler : IQueryHandler<GetUserQuery, string>
{
    public Task<string> HandleAsync(GetUserQuery query, CancellationToken cancellationToken = default)
        => Task.FromResult("ok");
}

Suppression Guidance

• Treat both diagnostics as correctness errors, not style warnings.
• Suppress only when handler registration happens outside analyzable source boundaries and that boundary is documented.
• Keep suppression local and include a comment with the registration path.

Test Coverage

Source: tests/LiteBus.Analyzers.UnitTests/MissingCommandHandlerAnalyzerTests.cs, tests/LiteBus.Analyzers.UnitTests/MissingQueryHandlerAnalyzerTests.cs