[ruby-core:119278] [Ruby master Feature#20757] Make rb_tracearg_(parameters|eval_script|instruction_sequence) public C-API

22 Sep 2024

      Issue #20757 has been updated by richardboehme (Richard Böhme).

Actually it seems like retrieving the method object using the `method_id` does not work well for super-calls. See this example:

``` ruby
TracePoint.new(:call) do  |tp|
  p tp.self
end.enable

class A
  def test
  end
end

class B < A
  def test = super
end

B.new.test
```

`TracePoint#self` will return the instance of B twice, which makes it hard to get the parameters of `A#test` without being able to call `TracePoint#parameters`. In general this makes it hard to track down the location of the method behind `TracePoint#method_id`, but this is another issue.

----------------------------------------
Feature #20757: Make rb_tracearg_(parameters|eval_script|instruction_sequence) public C-API
https://bugs.ruby-lang.org/issues/20757#change-109886

* Author: richardboehme (Richard Böhme)
* Status: Open
----------------------------------------
**Abstract**
As a C-extension developer when using tracepoints I include "ruby/debug.h". This includes most of TracePoint's API but it seems like the C-equivalents for TracePoint#parameters, TracePoint#eval_script and TracePoint#instruction_sequence are missing/not being exported in the header.

**Background**
Most APIs like rb_tracearg_return_value are exported in "ruby/debug.h". If I understand correctly, the implementations for those methods are located in "ruby/vm_trace.c". The following methods implemented in "ruby/vm_trace.c" are missing in "ruby/debug.h":
* rb_tracearg_parameters
* rb_tracearg_eval_script
* rb_tracearg_instruction_sequence

**Proposal**
I propose to add those methods to "ruby/debug.h". From my limiting understanding the change should be simple and not break backward compatibility, because we'd only need to add those function declarations to "ruby/debug.h".

I'd be open to contribute this change if it was approved.

**Use cases**
I'm implementing a method call tracer for Ruby using the C-extension API. I wanted to get information about the parameters that the called method receives. When writing in Ruby this can be done using the TracePoint#parameters method, but I could not find the equivalent C-API. A workaround is to retrieve the method object (using the method_id) and check the method parameters.  

**See also**

* Implementation of TracePoint#parameters in #14694 
* Implementation of TracePoint#eval_script and TracePoint#instruction_sequence in #15287 

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