Ruby Eval stacktrace position information

We’ve been often annoyed by warnings or exceptions like this: (eval):231: some error or warning. They make it very difficult to pinpoint the exact location of the problem.

The problem is usually cause by module_eval being called without file and line information. There’s an interesting write-up about eval and position information on Ola Bini’s blog. One of his readers observed that when using module_eval like this you’ll get the incorrect line number:

However, I noticed that if you write the heredoc inline you’ll get the correct line in the backtrace:

__LINE__ + 1 accounts for the line with the module_eval itself. I tested this with Ruby 1.8.6 and Ruby 1.9.1 and it applies for both, tough 1.9 at least puts more lines in the backtrace with the position of the module_eval call.

Passing __FILE__ and __LINE__ is better than skipping them, but can lead to false line numbers unless you use the 2nd form with the inlined heredoc.