1 files changed, 120 insertions, 0 deletions
diff --git a/lib/rubygems/commands/build_command.rb b/lib/rubygems/commands/build_command.rb
new file mode 100644
index 0000000000..cfe1f8ec3c
--- /dev/null
+++ b/lib/rubygems/commands/build_command.rb
@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+require_relative "../command"
+require_relative "../gemspec_helpers"
+require_relative "../package"
+require_relative "../version_option"
+
+class Gem::Commands::BuildCommand < Gem::Command
+  include Gem::VersionOption
+  include Gem::GemspecHelpers
+
+  def initialize
+    super "build", "Build a gem from a gemspec"
+
+    add_platform_option
+
+    add_option "--force", "skip validation of the spec" do |_value, options|
+      options[:force] = true
+    end
+
+    add_option "--strict", "consider warnings as errors when validating the spec" do |_value, options|
+      options[:strict] = true
+    end
+
+    add_option "-o", "--output FILE", "output gem with the given filename" do |value, options|
+      options[:output] = value
+    end
+  end
+
+  def arguments # :nodoc:
+    "GEMSPEC_FILE  gemspec file name to build a gem for"
+  end
+
+  def description # :nodoc:
+    <<-EOF
+The build command allows you to create a gem from a ruby gemspec.
+
+The best way to build a gem is to use a Rakefile and the Gem::PackageTask
+which ships with RubyGems.
+
+The gemspec can either be created by hand or extracted from an existing gem
+with gem spec:
+
+  $ gem unpack my_gem-1.0.gem
+  Unpacked gem: '.../my_gem-1.0'
+  $ gem spec my_gem-1.0.gem --ruby > my_gem-1.0/my_gem-1.0.gemspec
+  $ cd my_gem-1.0
+  [edit gem contents]
+  $ gem build my_gem-1.0.gemspec
+
+Gems can be saved to a specified filename with the output option:
+
+  $ gem build my_gem-1.0.gemspec --output=release.gem
+
+    EOF
+  end
+
+  def usage # :nodoc:
+    "#{program_name} GEMSPEC_FILE"
+  end
+
+  def execute
+    if build_path = options[:build_path]
+      Dir.chdir(build_path) { build_gem }
+      return
+    end
+
+    build_gem
+  end
+
+  private
+
+  def build_gem
+    gemspec = resolve_gem_name
+
+    if gemspec
+      build_package(gemspec)
+    else
+      alert_error error_message
+      terminate_interaction(1)
+    end
+  end
+
+  def build_package(gemspec)
+    spec = Gem::Specification.load(gemspec)
+    if spec
+      Gem::Package.build(
+        spec,
+        options[:force],
+        options[:strict],
+        options[:output]
+      )
+    else
+      alert_error "Error loading gemspec. Aborting."
+      terminate_interaction 1
+    end
+  end
+
+  def resolve_gem_name
+    return find_gemspec unless gem_name
+
+    if File.exist?(gem_name)
+      gem_name
+    else
+      find_gemspec("#{gem_name}.gemspec") || find_gemspec(gem_name)
+    end
+  end
+
+  def error_message
+    if gem_name
+      "Couldn't find a gemspec file matching '#{gem_name}' in #{Dir.pwd}"
+    else
+      "Couldn't find a gemspec file in #{Dir.pwd}"
+    end
+  end
+
+  def gem_name
+    get_one_optional_argument
+  end
+end