Issue #17881 has been updated by Eregon (Benoit Daloze).

Description updated

> A JIT that strip tracing code, and simply de-optimize when tracing is enabled doesn't seem that far fetched to me.

Yes, and I think it makes a lot of sense to deoptimize/recompile for e.g., :line and :call events (those have a huge perf impact).
But for `:class` I don't see how avoiding the check at the cost of deoptimization/recompilation would ever be worth it.

----------------------------------------
Feature #17881: Add a Module#const_added callback
https://bugs.ruby-lang.org/issues/17881#change-92110

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
----------------------------------------
### Use case

Autoloaders like `zeitwerk` need a callback when a new class or module is registered in the constant table.

Currently this is implemented with TracePoint's `:class` event. It works, but it is a bit unfortunate to have to use an API intended for debugging to implement production features.
It also has performance implications (albeit relatively minor), and [doesn't play well with MJIT](https://k0kubun.medium.com/ruby-3-jit-can-make-rails-faster-756310f235a).

### Proposal

I believe that if Ruby was to call `Module#const_added` when a constant is registered, Zeitwerk could get rid of TracePoint.

For now I implemented it as: `const_added(const_name)` for similarity with `method_added`. But maybe it could make sense to have the signature be `const_added(const_name, const_value)`.

Also since `method_removed` exists, maybe `const_removed` would need to be added for consistency.

### Links

Patch: https://github.com/ruby/ruby/pull/4521
Zeitwerk side discussion: https://github.com/fxn/zeitwerk/issues/135

cc @k0kubun



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:ruby-core-request / ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>