Smoke test for using the Kernel#set_trace_func in Ruby 2.x

method_trace.rb

 
# Official docs are a _bit_ light on specifcs
# http://ruby-doc.org/core-2.0.0/Kernel.html#method-i-set_trace_func
#
# There are other options if you are interested in a general trace:
# * ruby -r tracer your_script.rb
# * https://ruby-doc.org/core-2.3.0/TracePoint.html
#
# What I'd like to be able to do is create a helper module / class that can be added to any class like so:
# 
# class Foo
#   include MethodTracerHelper # could be included in test environments only by reopening the class!
# 
#   def super_cool
#     # doing interesting things
#   end
# end
#
# Foo.trace(:super_cool) # if no method is given then emit a stack trace for any invocation of any method on the class
#
# MethodTracer.do
#   # Do something else that will eventually call in to the Foo#super_cool method
# end
# 
# MethodTracer.do will output all stack traces for each invocation of :super_cool into a tmp directory
# like:
#   rails-root/tmp/method_tracer/2017-02-17-20:00:15/foo/super_cool/1/
# with files like:
#  stacktrace.txt
#  arguments.txt
class Foo
  def self.foo1()
    return "foo1"
  end

  def foo2(name, age)
    return "#{name} is #{age} years old"
  end
end

# emit a stack trace when the method :foo2 is called on Foo
Kernel.set_trace_func proc { |event, file, line, id, binding, klass|
  next unless klass == Foo && id == :foo2 && event == "call"
  puts "stacktrace: #{caller.join("\n")}"
  params = klass.instance_method(id).parameters.map {|_, name| name}
  vals = {}
  params.each do |name|
    vals[name] = binding.local_variable_get(name)
  end
  puts
  puts "arguments: #{vals}"
}

def foo_you_man
  Foo.new.foo2("Joe", 30)
end

def do_something_else
  foo_you_man
end

def do_something
  do_something_else
end

do_something