[ruby-core:115625] [Ruby master Bug#18886] Struct aref and aset don't trigger any tracepoints.

Issue #18886 has been updated by ko1 (Koichi Sasada).


Please merge it.

> I don't think this will affect performance unless TracePoint is used, because the same method caching is done in both cases.

Showing benchmarking result will help IMO to confirm there is no penalty.

----------------------------------------
Bug #18886: Struct aref and aset don't trigger any tracepoints.
https://bugs.ruby-lang.org/issues/18886#change-105557

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Given the following program, `thing.name` and `thing.shape` don't trigger `c_call` trace points (or any trace points actually).

```ruby
pp RUBY_VERSION

trace_point = TracePoint.new(:line, :call, :c_call, :a_call) do |trace|
  puts trace.event

  if trace.event == :call
    # Ruby doesn't always mark call-sites in sub-expressions, so we use this approach to compute a call site and mark it:
    if location = caller_locations(2, 1).first and path = location.path
      puts "> #{path}:#{location.lineno}:#{trace.event}"
    end
  end
  
  if path = trace.path
    puts "= #{path}:#{trace.lineno}:#{trace.event}"
  end
end

trace_point.enable

# This will trigger call trace points
class Thing
  def name
    :cat
  end
  
  def shape
    :square
  end
end
thing = Thing.new

# Thing = Struct.new(:name, :shape)
# thing = Thing.new(:cat, :rectangle)

[
  name: thing.name,
  shape: thing.shape,
]
```

## Current HEAD

```
= ../test.rb:30:line:
= ../test.rb:30:c_call:new
= ../test.rb:30:c_call:inherited
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:const_added
= ../test.rb:31:line:
= ../test.rb:31:c_call:new
= ../test.rb:31:c_call:initialize
= ../test.rb:34:line:
```

## Proposed PR

```
= ../test.rb:30:line:
= ../test.rb:30:c_call:new
= ../test.rb:30:c_call:inherited
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:singleton_method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:method_added
= ../test.rb:30:c_call:const_added
= ../test.rb:31:line:
= ../test.rb:31:c_call:new
= ../test.rb:31:c_call:initialize
= ../test.rb:34:line:
= ../test.rb:34:c_call:name
= ../test.rb:35:c_call:shape
```

The reason is the internal implementation of struct doesn't have trace point instrumentation in `vm_call_opt_struct_aset` or `vm_call_opt_struct_aref`.

Proposed fix: https://github.com/ruby/ruby/pull/6071 but this would need a review, maybe @jeremyevans0 and @ko1 can help.



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