Explanation of what I believe the problem to be with RedCloth 4.2.6 on Mac OS X

redcloth-4.2.6-test.md

Create a temporary directory for us to work in

$ cd ~
$ mkdir tmp-redcloth
$ cd tmp-redcloth

Install RedCloth 4.2.6

Use bundler to install RedCloth 4.2.6 into our temporary directory.

$ cat > Gemfile
source :rubygems

gem 'RedCloth', '4.2.6'
<ctrl-d>

$ bundle install --path gems
Fetching source index for http://rubygems.org/
Installing RedCloth (4.2.6) with native extensions 
Using bundler (1.0.7) 
Your bundle is complete! It was installed into ./gems

Attempt to load RedCloth

NOTE. I'm explicitly setting RUBYOPT to an empty string as my default setting is to require rubygems which will load the older, working, version I currently have installed.

$ cd gems/ruby/1.8/gems/RedCloth-4.2.6

Ensure that it's not just working by magic.

$ RUBYOPT='' ruby -e'require "RedCloth"'
-e:1:in `require': no such file to load -- RedCloth (LoadError)
  from -e:1

Check to see whether we can load it after we've added 'lib' to the load path.

$ RUBYOPT='' ruby -e'$LOAD_PATH << "lib"; require "RedCloth"'
-e:1:in `require': no such file to load -- RedCloth (LoadError)
  from -e:1

Check to see whether we can load it after we've added both 'lib' and 'lib/case_sensitive_require' to the load path.

$ RUBYOPT='' ruby -e'$LOAD_PATH << "lib"; $LOAD_PATH << "lib/case_sensitive_require"; require "RedCloth"'
./lib/case_sensitive_require/../redcloth.rb:12:in `require': no such file to load -- redcloth_scan (LoadError)
Couldn't load redcloth_scan
The $LOAD_PATH was:
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/site_ruby/1.8
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/site_ruby/1.8/i686-darwin10.3.0
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/site_ruby
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/vendor_ruby/1.8
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/vendor_ruby/1.8/i686-darwin10.3.0
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/vendor_ruby
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/1.8
/Users/chrisroos/.rvm/rubies/ree-1.8.7-2010.01/lib/ruby/1.8/i686-darwin10.3.0
.
lib
lib/case_sensitive_require
  from ./lib/case_sensitive_require/../redcloth.rb:12
  from ./lib/case_sensitive_require/RedCloth.rb:6:in `require'
  from ./lib/case_sensitive_require/RedCloth.rb:6
  from -e:1:in `require'
  from -e:1

It now complains that it's missing redcloth_scan. Let's find out where it is.

$ find . -name "redcloth_scan*"
./ext/redcloth_scan
./ext/redcloth_scan/redcloth_scan.bundle
./ext/redcloth_scan/redcloth_scan.c
./ext/redcloth_scan/redcloth_scan.o
./lib/lib/case_sensitive_require/redcloth_scan.bundle
./lib/redcloth_scan.jar

I think the version we need to use is the one in lib/lib/case_sensitive_require so let's add that to the load path and see what happens.

$ RUBYOPT='' ruby -e'$LOAD_PATH << "lib"; $LOAD_PATH << "lib/case_sensitive_require"; $LOAD_PATH << "lib/lib/case_sensitive_require"; require "RedCloth"'

And now we can require it successfully.

I'm not sure why the gem installer is installing redcloth_scan.bundle to lib/lib/case_sensitive_require. Seems very odd. What version of rubygems and bundler are you using?

I wonder if having "ext" in the require_paths would accomplish the same thing. That's how previous versions of RedCloth were. Pushing 4.2.7 with require_paths = ["lib", "lib/case_sensitive_require", "ext"] in the gemspec. If that doesn't work, I'll push the hack and then resign. ;-)