Warn about making non-release gems

Abbreviating the full version number of an intermediate build (eg.
"1.1b2-10-g61a374a") to the last tag (eg. "1.1b2") is evil, because it
means we end up labelling distinct versions of the software with the
same version number.

Unfortuantely, however, it is a necessary evil because RubyGems will
choke if passed an intermediate version number:

  Invalid gemspec in [command-t.gemspec]: Malformed version number string
  1.1b2-10-g61a374a
  ERROR:  While executing gem ... (NoMethodError)
      undefined method `mark_version' for nil:NilClass
      rake aborted!

So, we resort to using the abbreviated, misleading version number in
this case. We can at least mitigate this evilness by displaying a
warning if the user ever tries to build a gem for an intermediate
release, by adding a dependency on the ":check_tag" task.

Signed-off-by: Wincent Colaiuta <win@wincent.com>

Rakefile

@@ -12,6 +12,12 @@ def version
   `git describe`.chomp
 end
 
+def rubygems_version
+  # RubyGems will barf if we try to pass an intermediate version number
+  # like "1.1b2-10-g61a374a", so no choice but to abbreviate it
+  `git describe --abbrev=0`.chomp
+end
+
 def yellow
   "\033[33m"
 end
@@ -196,12 +202,11 @@ task :archive => :vimball do
 end
 
 desc 'Create the ruby gem package'
-task :gem do
+task :gem => :check_tag do
   sh "gem build command-t.gemspec"
 end
 
 desc 'Install the command-t ruby gem'
-task :install => :gem do
-  v = `git describe --abbrev=0`.chomp
-  sh "gem install command-t-#{v}.gem"
+task :install => :gem  do
+  sh "gem install command-t-#{rubygems_version}.gem"
 end

command-t.gemspec

@@ -1,5 +1,8 @@
 Gem::Specification.new do |s|
   s.name = "command-t"
+
+  # see note in the Rakefile about how intermediate version numbers
+  # can break RubyGems
   v = `git describe --abbrev=0`.chomp
   s.version = v