Exception#cause

exception.rb

=begin
https://docs.ruby-lang.org/ja/latest/class/Exception.html#I_CAUSE

[START] -> foo error.
[FooError-0] : foo error. -> ["exception_sample.rb:19:in `rescue in run'", "exception_sample.rb:16:in `run'", "exception_sample.rb:37:in `<main>'"]
[BarError-1] : bar error. -> ["exception_sample.rb:9:in `rescue in run'", "exception_sample.rb:6:in `run'", "exception_sample.rb:17:in `run'", "exception_sample.rb:37:in `<main>'"]
[ZeroDivisionError-2] : divided by 0 -> ["exception_sample.rb:7:in `/'", "exception_sample.rb:7:in `run'", "exception_sample.rb:17:in `run'", "exception_sample.rb:37:in `<main>'"]
[END]
=end

class FooError < StandardError;end
class BarError < StandardError;end

class Bar
  def run
    begin
      100 / 0
    rescue => e
      raise BarError, 'bar error.'
    end
  end
end

class Foo
  def run
    begin
      Bar.new.run
    rescue => e
      raise FooError, 'foo error.'
    end
  end
end

f = Foo.new

def dig_exception(e, count: 0, &block)
  yield e, count
  if e.cause.nil?
    return
  else
    count+=1
    dig_exception(e.cause, count: count, &block)
  end
end

begin
  f.run
rescue => e
  puts "[START] -> #{ e.message }"
  dig_exception(e) do |ex, index|
    puts "[#{ ex.class }-#{ index }] : #{ ex.message } -> #{ex.backtrace}"
  end
  puts "[END]"
end