Using exception.backtrace_locations

[oskarpearson]

Hi All

So I wrote a very similar library for our internal use :) I'm now looking to switch to the code_ownership gem instead.

code_ownership/lib/code_ownership.rb

Lines 120 to 138 in db89885

	def backtrace_with_ownership(backtrace)
	return [] unless backtrace
	# The pattern for a backtrace hasn't changed in forever and is considered
	# stable: https://github.com/ruby/ruby/blob/trunk/vm_backtrace.c#L303-L317
	#
	# This pattern matches a line like the following:
	#
	# ./app/controllers/some_controller.rb:43:in `block (3 levels) in create'
	#
	backtrace_line = %r{\A(#{Pathname.pwd}/|\./)?
	(?<file>.+) # Matches 'app/controllers/some_controller.rb'
	:
	(?<line>\d+) # Matches '43'
	:in\s
	`(?<function>.*)' # Matches "`block (3 levels) in create'"
	\z}x
	backtrace.lazy.filter_map do |line|

I see that code_ownership is using a regex to find the location. I originally did similar. However, I found exception.backtrace_locations which meant I didn't need to do so.

I prematurely submitted this discussion - so will add a followup as to how I use it shortly.

[oskarpearson]

begin
  whatever_fails_here
rescue => e
  puts e.backtrace_locations.first
end

The backtrace_locations is an array of Thread::Backtrace::Location objects https://ruby-doc.org/core-2.5.0/Thread/Backtrace/Location.html

def path_for_exception(exception)
  locations = exception.backtrace_locations

  # Filter out certain paths (eg: sidekiq middleware)
  locations = custom_filter(locations)

  locations.last&.absolute_path
end

[oskarpearson]

Also, this is neat:

code_ownership/lib/code_ownership/private.rb

Lines 61 to 69 in db89885

	sig { params(klass_string: T.nilable(String)).returns(T.nilable(String)) }
	def self.path_from_klass_string(klass_string)
	if klass_string
	path = Object.const_source_location(klass_string)&.first
	(path && Pathname.new(path).relative_path_from(Pathname.pwd).to_s) || nil
	else
	nil
	end
	end

I went a slightly different route - I hooked into the rails Autoloaders like this. fxn/zeitwerk#215 Perhaps it might be useful?

There was an issue with this for me, though. Classes that were embedded in different files (eg: a custom exception class defined in a containing class) weren't picked up without further coding:

class SomeClass
  class SomeException < ApplicationError; end
end