[ruby-core:120614] [Ruby master Feature#20757] Make rb_tracearg_(parameters|eval_script|instruction_sequence) public C-API

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

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


I've added the methods to debug.h and in my small test case it seemed to work without any problems. The PR is at https://github.com/ruby/ruby/pull/12553. Let me know if this is fine like this or if I should change anything!

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Feature #20757: Make rb_tracearg_(parameters|eval_script|instruction_sequence) public C-API
https://bugs.ruby-lang.org/issues/20757#change-111443

* Author: richardboehme (Richard Böhme)
* Status: Assigned
* Assignee: ko1 (Koichi Sasada)
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**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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