I created a hello world app with rails HelloWorld command. I ended up with many directories:
Should all this be under sources control? What would be a good default .hgignore file for a Ruby on Rails app folder?
The general rule is that if you've typed it by hand it should be in source control. If there are some scaffolding files that you didn't type but that can't be easily generated by your build system and don't often change, add them too. Avoid adding files that can be generated from other added files and non-mergeable files that change often.