Use UnpackedInstaller to install default gems.

Use UnpackedInstaller for installation of default gems similarly it is
already used to install bundled gems.

This allows to reuse RubyGems functionality instead of custom code full
of exceptions.

tool/rbinstall.rb

@@ -700,7 +700,7 @@ module RbInstall
           base = "#{prefix}#{relative_base}"
         when "lib"
           base = @base_dir
-          prefix = base.sub(/lib\/.*?\z/, "") + "lib/"
+          prefix = base.sub(/lib\/.*?\z/, "")
         else
           # other/something.gemspec ->
           #   [other/something.rb, other/something/foo.rb, ...]
@@ -763,7 +763,13 @@ module RbInstall
       mode = pattern == File.join(spec.bindir, '*') ? prog_mode : data_mode
       destdir = without_destdir(destination_dir)
       spec.files.each do |f|
+        next unless File.fnmatch(pattern, f)
         src = File.join(@src_dir, f)
+        # The `src` is fine for bundled gems. However, default gems have their
+        # binaries in `libexec`.
+        unless File.exist?(src)
+          src = File.join(@src_dir, 'libexec', File.basename(f))
+        end
         dest = File.join(destdir, f)
         makedirs(dest[/.*(?=\/)/m])
         install src, dest, :mode => mode
@@ -871,10 +877,10 @@ end
 # :startdoc:
 
 install?(:ext, :comm, :gem, :'default-gems', :'default-gems-comm') do
-  install_default_gem('lib', srcdir)
+  install_default_gem('lib', srcdir, bindir)
 end
 install?(:ext, :arch, :gem, :'default-gems', :'default-gems-arch') do
-  install_default_gem('ext', srcdir)
+  install_default_gem('ext', srcdir, bindir)
 end
 
 def load_gemspec(file, expanded = false)
@@ -902,12 +908,23 @@ def load_gemspec(file, expanded = false)
   spec
 end
 
-def install_default_gem(dir, srcdir)
+def install_default_gem(dir, srcdir, bindir)
   gem_dir = Gem.default_dir
   install_dir = with_destdir(gem_dir)
   prepare "default gems from #{dir}", gem_dir
   makedirs(Gem.ensure_default_gem_subdirectories(install_dir, $dir_mode).map {|d| File.join(gem_dir, d)})
 
+  options = {
+    :install_dir => with_destdir(gem_dir),
+    :bin_dir => with_destdir(bindir),
+    :ignore_dependencies => true,
+    :dir_mode => $dir_mode,
+    :data_mode => $data_mode,
+    :prog_mode => $script_mode,
+    :wrappers => true,
+    :format_executable => true,
+    :install_as_default => true,
+  }
   default_spec_dir = Gem.default_specifications_dir
 
   gems = Dir.glob("#{srcdir}/#{dir}/**/*.gemspec").map {|src|
@@ -926,25 +943,12 @@ def install_default_gem(dir, srcdir)
 
     full_name = "#{gemspec.name}-#{gemspec.version}"
 
+    gemspec.loaded_from = File.join srcdir, gemspec.spec_name
+
+    package = RbInstall::DirPackage.new gemspec
+    ins = RbInstall::UnpackedInstaller.new(package, options)
     puts "#{INDENT}#{gemspec.name} #{gemspec.version}"
-    gemspec_path = File.join(default_spec_dir, "#{full_name}.gemspec")
+    ins.install
-    open_for_install(gemspec_path, $data_mode) do
-      gemspec.to_ruby.gsub(/.*\0.*\n/, '')
-    end
-
-    specific_gem_dir = File.join(gem_dir, 'gems', full_name)
-
-    makedirs(specific_gem_dir)
-
-    unless gemspec.executables.empty? then
-      bin_dir = File.join(specific_gem_dir, gemspec.bindir)
-      makedirs(bin_dir)
-
-      gemspec.executables.map {|exec|
-        install File.join(srcdir, 'libexec', exec),
-                File.join(bin_dir, exec)
-      }
-    end
   end
 end