Try to setup Ruby SDK configuration (in RubyMine) manually - Main Menu | File | Settings | Project Structure | Ruby SDK and Gems, add SDK, press Add SDK.. button and select path to cygwin ruby interpreter. Then restart RubyMine.
If this helps: I have Cygwin at c:\cygwin ruby interpreter at c:\cygwin\bin\ruby.exe standard lib at c:\cygwin\lib\ruby\1.8 gems at c:\cygwin\lib\ruby\gems\1.8
..still doesn't work
Ilia,
Try to setup Ruby SDK configuration (in RubyMine) manually - Main Menu | File | Settings | Project Structure | Ruby SDK and Gems, add SDK, press Add SDK.. button and select path to cygwin ruby interpreter. Then restart RubyMine.
That's exact the way I do.
If this helps:
I have Cygwin at c:\cygwin
ruby interpreter at c:\cygwin\bin\ruby.exe
standard lib at c:\cygwin\lib\ruby\1.8
gems at c:\cygwin\lib\ruby\gems\1.8
There were some issues with loadpaths reported by Cygwin Ruby, I've added support for this case. It should be available in next RubyMine build