Ruby

The raise method supports setting the cause of an exception using the cause: keyword, but this behavior does not work as expected when calling Fiber#raise or Thread#raise, resulting in a TypeError. This breaks consistency with Kernel#raise and makes it difficult to attach causal chains to exceptions raised from other execution contexts.

The Problem¶

The following code behaves correctly when using Kernel#raise, correctly setting the cause:

cause = RuntimeError.new("cause")

begin
  raise RuntimeError, "boom", cause: cause
rescue => error
  pp error: error, cause: error.cause
end

Produces:

{error: #<RuntimeError: boom>, cause: #<RuntimeError: cause>}

However, using Fiber.current.raise or Thread.current.raise with the same arguments produces a TypeError:

begin
  Fiber.current.raise RuntimeError, "boom", cause: cause
rescue => error
  pp error: error, cause: error.cause
end

Results in:

{error: #<TypeError: backtrace must be an Array of String or an Array of Thread::Backtrace::Location>, cause: nil}

This occurs because the third argument is incorrectly interpreted as a backtrace, not as keyword arguments. A similar issue occurs with Thread#raise.

Proposed Solution¶

Update Fiber#raise and Thread#raise to accept and correctly interpret keyword arguments, including cause:, in the same manner as Kernel#raise. This would restore consistency across all raise implementations and allow causal exception chaining regardless of context. In other words, Fiber#raise and Thread#raise would be defined as the same interface as Kernel#raise.