From: "ioquatix (Samuel Williams)" <noreply@...>
Date: 2022-06-29T02:19:29+00:00
Subject: [ruby-core:109083] [Ruby master Bug#18886] Struct aref and aset don't trigger any tracepoints.

Issue #18886 has been reported by ioquatix (Samuel Williams).

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

* 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
trace_point = TracePoint.new(:line, :call, :c_call, :a_call) do |trace|
	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}:#{trace.method_id}"
		end
	end
	
	if path = trace.path
		puts "= #{path}:#{trace.lineno}:#{trace.event}:#{trace.method_id}"
	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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