Justified

A mini-gem to add missing causes to exception backtrace-s like Java has.

    from caused by: (AnError) an ugly bug
    from justified.rb:83:in `bad_code'
    from     ... skipped 4 lines

• Documentation: http://blog.pitr.ch/justified
• Source: https://github.com/pitr-ch/justified
• Blog: http://blog.pitr.ch/blog/categories/justified/

Example

Let's have following snippet:

def bad_code
  raise AnError, 'an ugly bug'
end

def handle_error(error)
  raise AnError, 'something went wrong'
end

def do_something
  bad_code
rescue => error
  handle_error error
end

do_something

When called it will produce:

justified.rb:93:in `handle_error': something went wrong (AnError)
    from justified.rb:89:in `rescue in do_something'
    from justified.rb:87:in `do_something'
    from justified.rb:96:in `<top (required)>'
    from -e:1:in `load'
    from -e:1:in `<main>'

The real problem an ugly bug is hidden. What will happen when justified is used?

require 'justified/stadard_error'
class AnError < StadardError; end

# ... rest of the snipper

It will produce:

justified.rb:93:in `handle_error': something went wrong (AnError)
    from justified.rb:89:in `rescue in do_something'
    from justified.rb:87:in `do_something'
    from justified.rb:96:in `<top (required)>'
    from -e:1:in `load'
    from -e:1:in `<main>'
    from caused by: (AnError) an ugly bug
    from justified.rb:83:in `bad_code'
    from     ... skipped 4 lines

Of course causes can be concatenated.

Usage

• require 'justified' to include Justified::Error to any exception you need manually
• require 'justified/standard_error' to have causes in all exceptions which are kind of StandardError

Behavior

When an exception is risen inside rescue block a cause is automatically recorded.

e = begin
      raise 'bug'
    rescue => error
      raise 'this does not work'
    end rescue $!
e.cause.message == 'bug' # => true

Cause can be set explicitly.

e = begin
      raise 'bug'
    rescue => error
      raise StandardError.new('this does not work', error)
    end rescue $!
e.cause.message == 'bug' # => true

Or if signature of .new is changed cause can be set with a setter #cause=

class InspectingError < StandardError
  def initialize(object)
    super object.inspect
  end
end

e = begin
      raise 'bug'
    rescue => error
      raise InspectingError.new(a: 'b').tap { |e| e.cause = error }
    end rescue $!
e.cause.message == 'bug' # => true

and

e = begin
      raise 'bug'
    rescue => error
      raise InspectingError.new(a: 'b')
    end rescue $!
e.cause.message == 'bug' # => true

will work as well.