This one took me quite some time to analyze but I now believe I have a pretty good idea of the problem.

Scenario:

• Create a subfolder called foo.
• Create a file called foo.rb with the following content:

puts "In foo.rb, __FILE__ is #{__FILE__}"

require './foo/bar/baz.rb'

• Create a subfolder of foo, called bar, in which the baz.rb is created with the following content:

puts "In baz.rb, __FILE__ is #{__FILE__}"

• Run the following command (this one has been using jruby-complete, don't know yet if it affects other variants also):

java -Djruby.compile.mode=FORCE -jar jruby-complete-1.7.6.jar c:\path\to\your\folder\foo/foo.rb

Expected output:

In foo.rb, __FILE__ is c:\path\to\your\folder\foo/foo.rb
In baz.rb, __FILE__ is c:\path\to\your\folderfoo/bar/baz.rb

Note that in the second line, there is a missing slash between folder and foo, causing all kinds of weird side effects.

Now, re-run without -Djruby.compile.mode=FORCE, and you'll see this:

In foo.rb, __FILE__ is c:\path\to\your\folder\foo/foo.rb
In baz.rb, __FILE__ is c:/path/to/your/folder/foo/bar/baz.rb

Note how the path is now correct, and not only that - all the slashes are now translated to forward slashes!

Why is this? How can jruby.compile.mode affect this? 😄

As noted, this has been verified with JRuby 1.7.6. I haven't tested with 1.7.8 but I find it quite likely that it's present there also.