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Bug #16829

open

Exceptions raised from within an enumerated method lose part of their stacktrace

Added by doliveirakn (Kyle d'Oliveira) almost 4 years ago. Updated almost 2 years ago.

Status:
Open
Assignee:
-
Target version:
-
[ruby-core:98135]

Description

Consider the following code:

class Test
  include Enumerable

  def each(&block)
    raise "Boom"
  end
end

def execution_method_a
  Test.new.to_enum(:each).next
end

def execution_method_b
  Test.new.each do
    # Never gets run
  end
end

begin
  execution_method_a
rescue RuntimeError => e
  puts "Using to_enum and next"
  puts e.message
  puts e.backtrace
end


begin
  execution_method_b
rescue RuntimeError => e
  puts "Calling a block directly"
  puts e.message
  puts e.backtrace
end

When this file (located at lib/script.rb) is run the result is:

Using to_enum and next
Boom
lib/script.rb:5:in `each'
lib/script.rb:1:in `each'
Calling a block directly
Boom
lib/script.rb:5:in `each'
lib/script.rb:14:in `execution_method_b'
lib/script.rb:29:in `<main>'

This is a little unusual. Effectively, if we create an enumerator and use next to iterate through the results, the backtrace is modified to the point where the calling method(s) are entirely lose. Notice when the each method is used directly and an exception is thrown, we see execution_method_b present in the stacktrace, but if we use next we do not see execution_method_a present at all.

This means that if there is some code that uses the enumerator/next approach deep within a callstack, the exception that comes out does not have any crucial information of where the call originated from.

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