add an installer constructor for paths

This allows us to provide objects that quack like a `Gem::Package` to
the installer class via `new`.

Author: tenderlove

lib/rubygems/commands/install_command.rb

@@ -275,7 +275,7 @@ def install_gem_without_dependencies name, req # :nodoc:
       gem = fetcher.download_to_cache dependency
     end
 
-    inst = Gem::Installer.new gem, options
+    inst = Gem::Installer.at gem, options
     inst.install
 
     require 'rubygems/dependency_installer'

lib/rubygems/commands/pristine_command.rb

@@ -156,7 +156,7 @@ def execute
           install_defaults.to_s['--env-shebang']
         end
 
-      installer = Gem::Installer.new(gem,
+      installer = Gem::Installer.at(gem,
                                      :wrappers => true,
                                      :force => true,
                                      :install_dir => spec.base_dir,

lib/rubygems/installer.rb

@@ -99,6 +99,14 @@ def exec_format
 
   end
 
+  ##
+  # Construct an installer object for the gem file located at +path+
+
+  def self.at path, options = {}
+    package = Gem::Package.new path
+    new package, options
+  end
+
   ##
   # Constructs an Installer instance that will install the gem located at
   # +gem+.  +options+ is a Hash with the following keys:
@@ -122,11 +130,18 @@ def exec_format
   # :build_args:: An Array of arguments to pass to the extension builder
   #               process. If not set, then Gem::Command.build_args is used
 
-  def initialize(gem, options={})
+  def initialize(package, options={})
     require 'fileutils'
 
     @options = options
-    @package = Gem::Package.new gem
+    if package.is_a? String
+      @package = Gem::Package.new package
+      if $VERBOSE
+        warn "constructing an Installer object with a string is deprecated. Please use Gem::Installer.at (called from: #{caller.first})"
+      end
+    else
+      @package = package
+    end
 
     process_options
 

lib/rubygems/installer_test_case.rb

@@ -176,15 +176,15 @@ def util_setup_gem(ui = @ui) # HACK fix use_ui to make this automatic
       end
     end
 
-    @installer = Gem::Installer.new @gem
+    @installer = Gem::Installer.at @gem
   end
 
   ##
   # Creates an installer for +spec+ that will install into +gem_home+.  If
   # +user+ is true a user-install will be performed.
 
   def util_installer(spec, gem_home, user=false)
-    Gem::Installer.new(spec.cache_file,
+    Gem::Installer.at(spec.cache_file,
                        :install_dir => gem_home,
                        :user_install => user)
   end

lib/rubygems/request_set.rb

@@ -159,7 +159,7 @@ def install options, &block # :yields: request, installer
 
       path = req.download cache_dir
 
-      inst = Gem::Installer.new path, options
+      inst = Gem::Installer.at path, options
 
       yield req, inst if block_given?
 

lib/rubygems/resolver/git_specification.rb

@@ -23,7 +23,7 @@ def add_dependency dependency # :nodoc:
   def install options = {}
     require 'rubygems/installer'
 
-    installer = Gem::Installer.new '', options
+    installer = Gem::Installer.at '', options
     installer.spec = spec
 
     yield installer if block_given?

lib/rubygems/resolver/specification.rb

@@ -89,7 +89,7 @@ def install options = {}
 
     gem = source.download spec, destination
 
-    installer = Gem::Installer.new gem, options
+    installer = Gem::Installer.at gem, options
 
     yield installer if block_given?
 

lib/rubygems/test_case.rb

@@ -488,7 +488,7 @@ def install_gem spec, options = {}
       gem = File.join(@tempdir, File.basename(spec.cache_file)).untaint
     end
 
-    Gem::Installer.new(gem, options.merge({:wrappers => true})).install
+    Gem::Installer.at(gem, options.merge({:wrappers => true})).install
   end
 
   ##

test/rubygems/simple_gem.rb

@@ -16,7 +16,7 @@
           @directory = options[:directory] || Gem.dir
           @force = options[:force]
 
-          gem = Gem::Installer.new(__FILE__).install(@force, @directory)
+          gem = Gem::Installer.at(__FILE__).install(@force, @directory)
           if options[:gen_rdoc]
             Gem::DocManager.new(gem).generate_rdoc
           end

test/rubygems/test_gem_commands_install_command.rb

@@ -910,7 +910,7 @@ def test_execute_uses_deps_a_gemdeps_with_a_path
       fetcher.gem 'r', '2.0', 'q' => nil
     end
 
-    i = Gem::Installer.new specs['q-1.0'].cache_file, :install_dir => "gf-path"
+    i = Gem::Installer.at specs['q-1.0'].cache_file, :install_dir => "gf-path"
     i.install
 
     assert File.file?("gf-path/specifications/q-1.0.gemspec"), "not installed"