Import interesting_backtrace_helper.rb from backtracie gem and use …

…it for testing the stack collector

(As the creator and sole copyright owner of that file in the
`backtracie` gem, taken from
<https://github.com/ivoanjo/backtracie/blob/1f6116ff5b07e87fe3e5be95a22c6a8e1210de8b/spec/unit/interesting_backtrace_helper.rb>
I am relicensing the file and its copyrights to belong to Datadog
similarly to the rest of the dd-trace-rb codebase).

This file is used as a single mega-complex test for the stack
sampling code, and is quite useful to spot regressions.

.rubocop.yml

@@ -22,6 +22,7 @@ AllCops:
     - 'integration/apps/*/bin/*'
     - 'integration/apps/*/Gemfile'
     - 'lib/datadog/profiling/pprof/pprof_pb.rb'
+    - 'spec/**/**/interesting_backtrace_helper.rb' # This file needs quite a few bizarre code patterns by design
   NewCops: disable # Don't allow new cops to be enabled implicitly.
 
 Layout/LineLength:

spec/datadog/profiling/collectors/interesting_backtrace_helper.rb

@@ -0,0 +1,185 @@
+# typed: ignore
+
+# This (very bizarre file) gets used from `stack_spec.rb`. It tries to reproduce the most interesting (contrived?) call
+# stack I can think of, with as many weird variants as possible.
+# The objective is to thoroughly test our stack trace sampling abilities.
+# Control flow goes from bottom of file to top (e.g. ClassA will be the top of the stack)
+
+# ----
+
+class IbhClassA
+  def hello
+    $ibh_ready_queue << true
+    sleep
+  end
+end
+
+module IbhModuleB
+  class IbhClassB < IbhClassA
+    def hello
+      super
+    end
+  end
+end
+
+module IbhModuleC
+  def self.hello
+    IbhModuleB::IbhClassB.new.hello
+  end
+end
+
+class IbhClassWithStaticMethod
+  def self.hello
+    IbhModuleC.hello
+  end
+end
+
+module IbhModuleD
+  def hello
+    IbhClassWithStaticMethod.hello
+  end
+end
+
+class IbhClassC
+  include IbhModuleD
+end
+
+$ibh_a_proc = proc { IbhClassC.new.hello }
+
+$ibh_a_lambda = lambda { $ibh_a_proc.call }
+
+class IbhClassD; end
+
+$ibh_class_d_object = IbhClassD.new
+
+def $ibh_class_d_object.hello
+  $ibh_a_lambda.call
+end
+
+class IbhClassE
+  def hello
+    $ibh_class_d_object.hello
+  end
+end
+
+class IbhClassG
+  def hello
+    raise "This should not be called"
+  end
+end
+
+module IbhContainsRefinement
+  module RefinesIbhClassG
+    refine IbhClassG do
+      def hello
+        if RUBY_VERSION >= "2.7.0"
+          IbhClassE.instance_method(:hello).bind_call(IbhClassF.new)
+        else
+          IbhClassE.instance_method(:hello).bind(IbhClassF.new).call
+        end
+      end
+    end
+  end
+end
+
+module IbhModuleE
+  using IbhContainsRefinement::RefinesIbhClassG
+
+  def self.hello
+    IbhClassG.new.hello
+  end
+end
+
+class IbhClassH
+  def method_missing(name, *_)
+    super unless name == :hello
+
+    IbhModuleE.hello
+  end
+end
+
+class IbhClassF < IbhClassE
+  def hello(arg1, arg2, test1, test2)
+    1.times {
+      IbhClassH.new.hello
+    }
+  end
+end
+
+IbhClassI = Class.new do
+  define_method(:hello) do
+    IbhClassF.new.hello(0, 1, 2, 3)
+  end
+end
+
+$ibh_singleton_class = Object.new.singleton_class
+
+def $ibh_singleton_class.hello
+  IbhClassI.new.hello
+end
+
+$ibh_anonymous_instance = Class.new do
+  def hello
+    $ibh_singleton_class.hello
+  end
+end.new
+
+$ibh_anonymous_module = Module.new do
+  def self.hello
+    $ibh_anonymous_instance.hello
+  end
+end
+
+def ibh_method_with_complex_parameters(a, b = nil, *c, (d), f:, g: nil, **h, &i)
+  $ibh_anonymous_module.hello
+end
+
+class IbhClassJ
+  def hello_helper
+    yield
+  end
+
+  def hello
+    hello_helper do
+      hello_helper do
+        ibh_method_with_complex_parameters(0, 1, 2, [3, 4], f: 5, g: 6, h: 7, &proc {})
+      end
+    end
+  end
+end
+
+class IbhClassK
+  def hello
+    eval("IbhClassJ.new.hello", binding, __FILE__, __LINE__)
+  end
+end
+
+class IbhClassL
+  def hello
+    IbhClassK.new.send(:instance_eval, "hello")
+  end
+end
+
+class IbhClassM
+  def hello
+    IbhClassL.new.send(:eval, "hello")
+  end
+end
+
+IbhClassN = Class.new do
+  define_method(:hello) do
+    1.times {
+      IbhClassM.new.hello
+    }
+  end
+end
+
+def ibh_top_level_hello
+  IbhClassN.new.hello
+end
+
+1.times {
+  1.times {
+    eval("ibh_top_level_hello()")
+  }
+}

spec/datadog/profiling/collectors/stack_spec.rb

@@ -171,6 +171,29 @@ def call_sleep
       end
     end
     # rubocop:enable Style/EvalWithLocation
+
+    context 'when sampling the interesting backtrace helper' do
+      # rubocop:disable Style/GlobalVars
+      let(:do_in_background_thread) do
+        proc do |ready_queue|
+          $ibh_ready_queue = ready_queue
+          load("#{__dir__}/interesting_backtrace_helper.rb")
+        end
+      end
+
+      after do
+        $ibh_ready_queue = nil
+      end
+      # rubocop:enable Style/GlobalVars
+
+      it 'matches the Ruby backtrace API' do
+        expect(gathered_stack).to eq reference_stack
+      end
+
+      it 'has a sleeping frame at the top of the stack' do
+        expect(reference_stack.first).to match(hash_including(base_label: 'sleep'))
+      end
+    end
   end
 
   context 'when sampling a thread with a stack that is deeper than the configured max_frames' do