[ruby-core:96094] [Ruby master Bug#16383] TracePoint does not report calls to attribute reader methods

Issue #16383 has been updated by jeremyevans0 (Jeremy Evans).

File tracepoint-attr-16383.patch added

I'm not sure if skipping tracing for these methods is on purpose for performance reasons or not, but I agree it would be useful to be able to trace such method calls.  Attached is a patch that implements tracing for `attr_reader`/`attr_writer` method calls.  I'm not sure it is correct, but with the following code:

```ruby
class Person
  attr_accessor :first_name
  attr_accessor :last_name
  def name
    "#{self.last_name}, #{self.first_name}"
  end
end

person = Person.new
trace = TracePoint.new(:c_call, :call) do |tp|
  p [tp.path, tp.lineno, tp.defined_class, tp.event, tp.callee_id]
end
trace.enable
person.first_name = 'Josh'
person.last_name = 'McGibbon'
person.name
trace.disable
```

I get the following output:

```
["t.rb", 14, Person, :c_call, :first_name=]
["t.rb", 15, Person, :c_call, :last_name=]
["t.rb", 4, Person, :call, :name]
["t.rb", 5, Person, :c_call, :last_name]
["t.rb", 5, Person, :c_call, :first_name]
["<internal:trace_point>", 231, TracePoint, :call, :disable]
```

Note that because `attr_reader`/`attr_writer` are implemented in C, I choose `:c_call` and `:c_return` instead of `:call` and `:return`.  There is at least a bug in that `method_id` is incorrect, showing the instance variable symbol instead of the method symbol.

----------------------------------------
Bug #16383: TracePoint does not report calls to attribute reader methods
https://bugs.ruby-lang.org/issues/16383#change-82952

* Author: AndyMaleh (Andy Maleh)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.7p206 (2019-10-01 revision 67816) [x86_64-darwin19]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
TracePoint does not report calls to attribute reader methods (e.g. methods defined using `attr_accessor` or `attr_reader`.)

**Code sample to demonstrate:**

```ruby
class Person
  attr_accessor :first_name
  attr_accessor :last_name
  def name
    "#{self.last_name}, #{self.first_name}"
  end
end

person = Person.new
person.first_name = 'Josh'
person.last_name = 'McGibbon'
trace = TracePoint.new(:call) do |tp|
  p [tp.path, tp.lineno, tp.defined_class, tp.event, tp.method_id]
end
trace.enable
person.name
trace.disable

class Person
  attr_writer :first_name
  attr_writer :last_name
  def name
    "#{self.last_name}, #{self.first_name}"
  end
  def first_name
    @first_name
  end
  def last_name
    @last_name
  end
end

person = Person.new
person.first_name = 'Josh'
person.last_name = 'McGibbon'
trace = TracePoint.new(:call) do |tp|
  p [tp.path, tp.lineno, tp.defined_class, tp.event, tp.method_id]
end
trace.enable
person.name
trace.disable
```

**Output:**

```
["trace_point_issue.rb", 4, Person, :call, :name]
["trace_point_issue.rb", 22, Person, :call, :name]
["trace_point_issue.rb", 28, Person, :call, :last_name]
["trace_point_issue.rb", 25, Person, :call, :first_name]
```

Please note how `:last_name` and `:first_name` show up only the second time `Person#name` is called. In other words, they show up when defined as actual methods using `def` keyword, but not when defined via `attr_accessor`.

**Expected Output:**

```
["trace_point_issue.rb", 22, Person, :call, :name]
["trace_point_issue.rb", 28, Person, :call, :last_name]
["trace_point_issue.rb", 25, Person, :call, :first_name]
["trace_point_issue.rb", 22, Person, :call, :name]
["trace_point_issue.rb", 28, Person, :call, :last_name]
["trace_point_issue.rb", 25, Person, :call, :first_name]
```

Your help in fixing or explaining this issue is greatly appreciated.

My goal is to monitor all method calls when invoking a certain method (Person#name in this case) in order to attach observers to them dynamically for desktop UI data-binding use in my open-source project Glimmer: https://github.com/AndyObtiva/glimmer

Cheers,

Andy Maleh

---Files--------------------------------
trace_point_issue.rb (791 Bytes)
tracepoint-attr-16383.patch (1.97 KB)


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