[ruby-core:64867] [ruby-trunk - Feature #10211] Implement Signal.current_trap(sig)

Issue #10211 has been updated by David Rodr鱈guez.


I happen to need something like this too.

I'd like to be able to override RSpec's trap somehow. For example, if someone types something in byebug or pry's prompt, we surely don't want to quit rspec but only empty the input written so far by the user and print another prompt.

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Feature #10211: Implement Signal.current_trap(sig)
https://bugs.ruby-lang.org/issues/10211#change-48731

* Author: Kyrylo Silin
* Status: Feedback
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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Here's pseudocode by ko1:

~~~
def trap2(sig)
  previous_proc = Signal.current_trap(sig)
  Signal.trap(sig){
    previous_proc.call if previous_proc
    yield
  }
end
 
trap2(:INT){...}
~~~

## Motivation

I'm developing a gem that allows using multiple callbacks for a trap: [[https://github.com/kyrylo/multitrap]]
It's pretty simple (and slightly broken). The problem is that if you earlier had defined traps and then
required my library, it would discard your previously defined callbacks.
The library overrides `Signal.trap` and stores callbacks in a hash. However, it stores only new callbacks.
I cannot access previously defined callbacks for signals. They are stored in `GET_VM()->trap_list`, which
isn't exposed neither to Ruby nor to the C extension API. I know when you define a `trap`, it returns a proc.
However, nobody typicaly stores it, so there's no way to access it. So if my gem loads after this assignment,
I'm unable to capture that proc, hence I always overwrite previous "traps". This library might be useful if you
want to define a trap that conflicts with some other gem you depend on, which defines its own trap for the
same signal.

So I need some way to access the callbacks.



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