[DRE-maint] Bug#529663: rubygems1.8: Gem::Ext::RakeBuilder uses the wrong executable name for rake

[Ken Bloom]

Package: rubygems1.8
Version: 1.3.2-1
Severity: important

SYMPTOMS:
=========

Trying to install the ffi gem in Debian's ruby 1.8, I get the
following error:

[bloom at cat-in-the-hat ~]$ gem install ffi
Building native extensions.  This could take a while...
ERROR:  Error installing ffi:
	ERROR: Failed to build gem native extension.

rake1.8 RUBYARCHDIR=/home/bloom/.gem/ruby/1.8/gems/ffi-0.3.5/lib RUBYLIBDIR=/home/bloom/.gem/ruby/1.8/gems/ffi-0.3.5/lib
sh: rake1.8: command not found

I have rake installed from Debian's rake package, and the binary to
run rake is /usr/bin/rake (so no rake 1.8 exists).
ii  rake                     0.8.4-1                  a ruby build program

CAUSE:
======

Ultimately, this is a rubygems problem in
/usr/lib/ruby/1.8/rubygems/ext/rake_builder.rb
Rubygems determines the rake command to run by executing:

cmd = ENV['rake'] || Gem.bin_path('rake') rescue Gem.default_exec_format % 'rake'

So let's check:

ENV['rake']
  --> not set (though this will give me a workaround in the meantime)
Gem.bin_path('rake')
  --> rake isn't installed from a gem -- it's from the debian package
Gem.default_exec_format % 'rake'
  --> Gem.default_exec_format is "%s1.8", so when formatting "rake"
      with that, we get rake1.8, a binary that doesn't exist.


WORKAROUND:
===========
$ rake=/usr/bin/rake gem install ffi

PROPOSED SOLUTION:
==================
In the short term, add a check to see if /usr/bin/rake is installed,
and if so then use that.

In the longer term, it would help to create some sort of equivalence
mechanism so that Ruby can identify debian packages as being
equivalent to gems.

-- System Information:
Debian Release: squeeze/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.29-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages rubygems1.8 depends on:
ii  rdoc1.8                     1.8.7.72-3.1 Generate documentation from Ruby s
ii  ruby1.8                     1.8.7.72-3.1 Interpreter of object-oriented scr

rubygems1.8 recommends no packages.

Versions of packages rubygems1.8 suggests:
ii  build-essential             11.4         Informational list of build-essent
ii  ruby1.8-dev                 1.8.7.72-3.1 Header files for compiling extensi
pn  rubygems-doc                <none>       (no description available)

-- no debconf information