Import RubyGems trunk revision 1493.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@13862 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/commands/build_command.rb

@@ -0,0 +1,53 @@
+require 'rubygems/command'
+require 'rubygems/builder'
+
+class Gem::Commands::BuildCommand < Gem::Command
+
+  def initialize
+    super('build', 'Build a gem from a gemspec')
+  end
+
+  def arguments # :nodoc:
+    "GEMSPEC_FILE  gemspec file name to build a gem for"
+  end
+
+  def usage # :nodoc:
+    "#{program_name} GEMSPEC_FILE"
+  end
+
+  def execute
+    gemspec = get_one_gem_name
+    if File.exist?(gemspec)
+      specs = load_gemspecs(gemspec)
+      specs.each do |spec|
+        Gem::Builder.new(spec).build
+      end
+    else
+      alert_error "Gemspec file not found: #{gemspec}"
+    end
+  end
+
+  def load_gemspecs(filename)
+    if yaml?(filename)
+      result = []
+      open(filename) do |f|
+        begin
+          while not f.eof? and spec = Gem::Specification.from_yaml(f)
+            result << spec
+          end
+        rescue Gem::EndOfYAMLException => e
+          # OK
+        end
+      end
+    else
+      result = [Gem::Specification.load(filename)]
+    end
+    result
+  end
+
+  def yaml?(filename)
+    line = open(filename) { |f| line = f.gets }
+    result = line =~ %r{^--- *!ruby/object:Gem::Specification}
+    result
+  end
+end