only define gem packaging tasks if rubygems is already loaded

Rakefile

@@ -5,6 +5,11 @@ require 'fileutils'
 task :default => :test
 task :spec => :test
 
+def source_version
+  line = File.read('lib/sinatra/base.rb')[/^\s*VERSION = .*/]
+  line.match(/.*VERSION = '(.*)'/)[1]
+end
+
 # SPECS ===============================================================
 
 Rake::TestTask.new(:test) do |t|
@@ -12,50 +17,23 @@ Rake::TestTask.new(:test) do |t|
   t.ruby_opts = ['-rubygems -I.'] if defined? Gem
 end
 
-# PACKAGING ============================================================
-
-# Load the gemspec using the same limitations as github
-def spec
-  require 'rubygems' unless defined? Gem::Specification
-  @spec ||= eval(File.read('sinatra.gemspec'))
+# Rcov ================================================================
+namespace :test do
+  desc 'Mesures test coverage'
+  task :coverage do
+    rm_f "coverage"
+    rcov = "rcov --text-summary --test-unit-only -Ilib"
+    system("#{rcov} --no-html --no-color test/*_test.rb")
+  end
 end
 
-def package(ext='')
-  "pkg/sinatra-#{spec.version}" + ext
-end
-
-desc 'Build packages'
-task :package => %w[.gem .tar.gz].map {|e| package(e)}
-
-desc 'Build and install as local gem'
-task :install => package('.gem') do
-  sh "gem install #{package('.gem')}"
-end
-
-directory 'pkg/'
-CLOBBER.include('pkg')
-
-file package('.gem') => %w[pkg/ sinatra.gemspec] + spec.files do |f|
-  sh "gem build sinatra.gemspec"
-  mv File.basename(f.name), f.name
-end
-
-file package('.tar.gz') => %w[pkg/] + spec.files do |f|
-  sh <<-SH
-    git archive \
-      --prefix=sinatra-#{source_version}/ \
-      --format=tar \
-      HEAD | gzip > #{f.name}
-  SH
-end
-
-# Website ============================================================
+# Website =============================================================
 # Building docs requires HAML and the hanna gem:
 #   gem install mislav-hanna --source=http://gems.github.com
 
+desc 'Generate RDoc under doc/api'
 task 'doc'     => ['doc:api']
 
-desc 'Generate Hanna RDoc under doc/api'
 task 'doc:api' => ['doc/api/index.html']
 
 file 'doc/api/index.html' => FileList['lib/**/*.rb','README.rdoc'] do |f|
@@ -73,14 +51,45 @@ file 'doc/api/index.html' => FileList['lib/**/*.rb','README.rdoc'] do |f|
 end
 CLEAN.include 'doc/api'
 
-# Gemspec Helpers ====================================================
+# PACKAGING ============================================================
 
-def source_version
-  line = File.read('lib/sinatra/base.rb')[/^\s*VERSION = .*/]
-  line.match(/.*VERSION = '(.*)'/)[1]
-end
+if defined?(Gem)
+  # Load the gemspec using the same limitations as github
+  def spec
+    require 'rubygems' unless defined? Gem::Specification
+    @spec ||= eval(File.read('sinatra.gemspec'))
+  end
 
-task 'sinatra.gemspec' => FileList['{lib,test,compat}/**','Rakefile','CHANGES','*.rdoc'] do |f|
+  def package(ext='')
+    "pkg/sinatra-#{spec.version}" + ext
+  end
+
+  desc 'Build packages'
+  task :package => %w[.gem .tar.gz].map {|e| package(e)}
+
+  desc 'Build and install as local gem'
+  task :install => package('.gem') do
+    sh "gem install #{package('.gem')}"
+  end
+
+  directory 'pkg/'
+  CLOBBER.include('pkg')
+
+  file package('.gem') => %w[pkg/ sinatra.gemspec] + spec.files do |f|
+    sh "gem build sinatra.gemspec"
+    mv File.basename(f.name), f.name
+  end
+
+  file package('.tar.gz') => %w[pkg/] + spec.files do |f|
+    sh <<-SH
+      git archive \
+        --prefix=sinatra-#{source_version}/ \
+        --format=tar \
+        HEAD | gzip > #{f.name}
+    SH
+  end
+
+  task 'sinatra.gemspec' => FileList['{lib,test,compat}/**','Rakefile','CHANGES','*.rdoc'] do |f|
     # read spec file and split out manifest section
     spec = File.read(f.name)
     head, manifest, tail = spec.split("  # = MANIFEST =\n")
@@ -100,14 +109,5 @@ task 'sinatra.gemspec' => FileList['{lib,test,compat}/**','Rakefile','CHANGES','
     spec = [head,manifest,tail].join("  # = MANIFEST =\n")
     File.open(f.name, 'w') { |io| io.write(spec) }
     puts "updated #{f.name}"
-end
-
-# Rcov ==============================================================
-namespace :test do
-  desc 'Mesures test coverage'
-  task :coverage do
-    rm_f "coverage"
-    rcov = "rcov --text-summary --test-unit-only -Ilib"
-    system("#{rcov} --no-html --no-color test/*_test.rb")
   end
 end