Playing with TracePoint and PlantUML Sequence Diagrams.

spike.rb

class Worker
  def actually_do_work
    puts "workin!"
  end
end

class Bar
  def nope_maybe_this_does(worker = Worker)
    worker.new.actually_do_work
    worker.new.actually_do_work
  end
end

class Foo
  def does_this_do_any_work(barrer = Bar)
    b = barrer.new
    b.nope_maybe_this_does
    b.nope_maybe_this_does
  end
end

Call = Struct.new(:caller, :callee, :method) do
  def direction
    "->"
  end
end

Return = Struct.new(:caller, :callee, :method) do
  def direction
    "<--"
  end
end

class System; end

stack = []
actors = { System.new => true }
sequence = []

calls = TracePoint.new(:call) do |tp|
  actors[tp.self] = true
  call = Call.new(tp.defined_class, tp.defined_class, tp.method_id)
  stack.push(call)
  sequence << call
end

returns= TracePoint.new(:return) do |tp|
  actors[tp.self] = true
  the_caller = stack[-2]
  stack.pop.caller = the_caller ? the_caller.caller : System
end

[calls, returns].each(&:enable)

Foo.new.does_this_do_any_work

[calls, returns].each(&:disable)

puts stack

output = []
output << "@startuml"
actors.map { |object, _| object.class }.uniq.each do |object_class|
  output << %(participant #{object_class})
end

sequence.each do |call|
  output << "#{call.caller} #{call.direction} #{call.callee}: #{call.method}" if call.is_a? Call
end

output << "@enduml"

File.write "tmp.plantuml", output.join("\n")

tmp.plantuml

@startuml
participant System
participant Foo
participant Bar
participant Worker
System -> Foo: does_this_do_any_work
Foo -> Bar: nope_maybe_this_does
Bar -> Worker: actually_do_work
Bar -> Worker: actually_do_work
Foo -> Bar: nope_maybe_this_does
Bar -> Worker: actually_do_work
Bar -> Worker: actually_do_work
@enduml

Generates: