Why does my rdebug session say "*** No sourcefile available"

I'm not sure what the pattern of behaviour is but some programs - notably simple rack.ru based ones running in thin - can't easily be debugged. When a breakpoint is tripped, no source is available

Note this isn't the same as t开发者_开发技巧his other S.O. [issue][1]

[1]: In ruby, why does my IRB interactive debugging session always say "No sourcefile available" session-always-say-no-sourcefile

---

err, actually found the source of the problem. I had a Dir.chdir buried in my code. Any debugger call after that couldn't find the source, a call before worked fine.

Hopefully that helps somebody at some time.