[ruby-core:120408] [Ruby master Bug#20981] rb_undefine_finalizer is missing

[KitaitiMakoto via ruby-core <ruby-core@ml.ruby-lang.org>]

Issue #20981 has been updated by KitaitiMakoto (真 北市).


Thank you! I confirmed my code works fine in Ruby `master` branch.

----------------------------------------
Bug #20981: rb_undefine_finalizer is missing
https://bugs.ruby-lang.org/issues/20981#change-111188

* Author: KitaitiMakoto (真 北市)
* Status: Closed
* ruby -v: 3.4.1
* Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED, 3.4: REQUIRED
----------------------------------------
Merry Christmas!

I encountered an error like "dyld[89037]: missing symbol called" in an extension which uses`rb_undefine_finalizer` in Ruby 3.4.1. It works fine in Ruby 3.3.6.

The function defined in [ruby/include/ruby/internal/gc.h](https://github.com/ruby/ruby/blob/v3_4_1/include/ruby/internal/gc.h#L315-L326) but seems removed from [ruby/gc.c](https://github.com/ruby/ruby/blob/v3_4_1/gc.c). Could you consider restore the implementation or remove the function from `gc.h`?

Reproducible code:

### extconf.rb ###
```ruby
require "mkmf"
create_makefile "undefine_finalizer_bug"
```


### undefine_finalizer_bug.c ###
```c
#include<ruby.h>

static VALUE s_undefine_finalizer(VALUE self) {
  rb_undefine_finalizer(self);
  return Qnil;
}

void Init_undefine_finalizer_bug(void) {
  VALUE klass = rb_define_class("UndefineFinalizerBug", rb_cObject);
  rb_define_singleton_method(klass, "undefine_finalizer", s_undefine_finalizer, 0);
}
```

### undefine-finalizer-bug.rb ###
```ruby
require "undefine_finalizer_bug.so"

finalizer = proc {
  puts "Finalizer called"
}

ObjectSpace.define_finalizer(UndefineFinalizerBug, finalizer)
UndefineFinalizerBug.new
UndefineFinalizerBug.undefine_finalizer
GC.start
```

### Running ###
#### Ruby 3.4.1 ##
```
% ruby ./extconf.rb && make && ruby -v -I. ./undefine-finalizer-bug.rb
creating Makefile
linking shared-object undefine_finalizer_bug.bundle
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24]
dyld[2436]: missing symbol called
[1]    2436 abort      ruby -v -I. ./undefine-finalizer-bug.rb
```

#### Ruby 3.3.6 ####
```
% chruby-exec 3.3.6 -- ruby ./extconf.rb && make && chruby-exec 3.3.6 -- ruby -v -I. ./undefine-finalizer-bug.rb
creating Makefile
linking shared-object undefine_finalizer_bug.bundle
ruby 3.3.6 (2024-11-05 revision 75015d4c1f) [arm64-darwin24]
```


Thank you.




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