Bug #12588: When an exception is re-raised in the "rescue" clause, the back trace does not contain the line in that clause

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-darwin14]
• Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN

[hasari (Hiro Asari)]

Given:

$ cat -n foo.rb 
     1  def foo
     2    raise StandardError
     3  rescue StandardError => e
     4    raise e
     5  end
     6
     7  foo

one would reasonably expect to see line 4 to be in the back trace when this file is executed, but one does not.

$ ruby -v foo.rb
ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-darwin14]
foo.rb:2:in `foo': StandardError (StandardError)
        from foo.rb:7:in `<main>'

[nobu (Nobuyoshi Nakada)]

I think it's intentional, and don't see why it should contain a new line.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

I don't see any "reasonable expectancy". Use-case? Probably you want to use Exception#cause?

Matz.

[hasari (Hiro Asari)]

The current stacktrace is misleading. Without line 4 in it, the implication is that the exception was found on line 2, and was not caught by rescue. In this simple case, the stack trace should contain lines [4,7], not [2,7].

I am not sure how I can use Exception#cause. I tried:

$ cat -n foo.rb
     1  def foo
     2    raise StandardError
     3  rescue StandardError => e
     4    puts e.cause.class
     5    raise e.cause
     6  end
     7
     8  foo
$ ruby -v foo.rb
ruby 2.4.0dev (2016-09-21 trunk 56200) [x86_64-darwin15]
NilClass
foo.rb:5:in `raise': exception object expected (TypeError)
        from foo.rb:5:in `rescue in foo'
        from foo.rb:2:in `foo'
        from foo.rb:8:in `<main>'

[shyouhei (Shyouhei Urabe)]

Hiro Asari wrote:

I am not sure how I can use Exception#cause.

Exception#cause makes sense when you raise another exception from inside of a rescue clause. Take a look at this example:

def foo
  raise 'raised in #foo'
end

def bar
  foo
rescue
  raise 'raised in #bar'
end

def baz
  bar
rescue => e
  p e        # => #<RuntimeError: raised in #bar>
  p e.cause  # => #<RuntimeError: raised in #foo>
end

baz