Rcov is now in a state where it is completely impossible to use. 

1. It has several issues with the current REXML see here:

http://www.ruby-forum.com/topic/128842

I'm getting these errors on every rails project.

2. Besides those error mentioned I'm getting a stack level to deep for indenting / wrapping the output.

/opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:131:in `wrap': stack level too deep (SystemStackError)
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:131:in `wrap'
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:90:in `write_text'
	from /opt/local/lib/ruby/1.8/rexml/formatters/default.rb:50:in `write'
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:75:in `write_element'
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:73:in `each'
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:73:in `write_element'
	from /opt/local/lib/ruby/1.8/rexml/formatters/default.rb:31:in `write'
	from /opt/local/lib/ruby/1.8/rexml/formatters/pretty.rb:75:in `write_element'
	 ... 12 levels...
	from /opt/local/lib/ruby/gems/1.8/gems/rcov-0.8.1.2.0/lib/rcov.rb:640:in `each'
	from /opt/local/lib/ruby/gems/1.8/gems/rcov-0.8.1.2.0/lib/rcov.rb:640:in `dump_coverage_info'
	from /opt/local/lib/ruby/gems/1.8/gems/rcov-0.8.1.2.0/bin/rcov:421
	from /opt/local/lib/ruby/1.8/test/unit.rb:278

3.  rexml/formatters/pretty.rb:131:in `[]': no implicit conversion from nil to integer (TypeError)
which is probably just an issue with the patches from the forum post mentioned above.

Currently rcov just doesn't work for us anymore.

Date: 2009-02-25 04:07
Sender: Bryan McLellan

These are mostly issues with REXML [1], the patches in place
in ruby 1.8.6 don't get applied when you're running ruby 1.8.7
without patching. [2]

[1] http://enfranchisedmind.com/blog/2008/03/24/rexml-dynamic-typ
ing-lose/
[2] https://bugs.launchpad.net/ubuntu/+source/rcov/+bug/327753

Date: 2009-02-06 18:16
Sender: Jan Rüegg

"I changed line to check for ruby 1.8.7 and rcov works
now."

=> Same for me, changing that made rcov work with ruby 1.8.7
...

Date: 2008-11-10 21:49
Sender: Vitalie Lazu

I use ruby 1.8.7 and have the same issue, while investigating
I found in report.rb:

if RUBY_VERSION == "1.8.6" && defined?
REXML::Formatters::Transitive

I changed line to check for ruby 1.8.7 and rcov works now.