Looking for help on contributing to Rails

I’m looking for some advice on contributing to Rails (and other large projects).

I will provide a specific scenario.

Here is a pull request that was merged a year ago.

In the past month, three people have commented that this introduces another issue under certain circumstances (you have an index on a field).

What do I do if I want to take a shot at working on this?

The file that was edited has had 10 commits since the pull request in question was merged and currently looks a bit different than it did 10 commits ago.

Here are some specific questions:

I’m not sure I fully understand what the original issue was (why a pull request was submitted in the first place). Therefore, if I wanted to set up a Rails project that exhibited the issue that the pull request was created to fix, how would I do that? In other words, how do I determine which version of Rails contains the version of the autosave_associaton.rb file as it was immediately before the pull request was merged? (Or can I install a specific version of Rails based on a Rails Github repo commit?)

If I do end up implementing a fix for this in the current version (Rails 4.0), how can I also issue the same fix for a previous version of Rails (3.2.x)?

Thanks.

If you don't get anything helpful here (this list is generally for
help with using rails rather than developing it) you could try the
rails-core mailing list.

Colin