52 files changed, 1012 insertions, 204 deletions

diff --git a/lib/rubygems/LICENSE.txt b/lib/rubygems/LICENSE.txt
index db88c5e118..8a0a51dec1 100644
--- a/lib/rubygems/LICENSE.txt
+++ b/lib/rubygems/LICENSE.txt
@@ -1,53 +1,54 @@
 RubyGems is copyrighted free software by Chad Fowler, Rich Kilmer, Jim
 Weirich and others.  You can redistribute it and/or modify it under
-either the terms of the GPL (see the GPL.txt file), or the conditions
-below:
+either the terms of the MIT license (see the file MIT.txt), or the
+conditions below:
 
-  1. You may make and give away verbatim copies of the source form of the
-     software without restriction, provided that you duplicate all of the
-     original copyright notices and associated disclaimers.
+1. You may make and give away verbatim copies of the source form of the
+   software without restriction, provided that you duplicate all of the
+   original copyright notices and associated disclaimers.
 
-  2. You may modify your copy of the software in any way, provided that
-     you do at least ONE of the following:
+2. You may modify your copy of the software in any way, provided that
+   you do at least ONE of the following:
 
-       a) place your modifications in the Public Domain or otherwise
-          make them Freely Available, such as by posting said
-	  modifications to Usenet or an equivalent medium, or by allowing
-	  the author to include your modifications in the software.
+   a. place your modifications in the Public Domain or otherwise
+      make them Freely Available, such as by posting said
+      modifications to Usenet or an equivalent medium, or by allowing
+      the author to include your modifications in the software.
 
-       b) use the modified software only within your corporation or
-          organization.
+   b. use the modified software only within your corporation or
+      organization.
 
-       c) rename any non-standard executables so the names do not conflict
-	  with standard executables, which must also be provided.
+   c. give non-standard executables non-standard names, with
+      instructions on where to get the original software distribution.
 
-       d) make other distribution arrangements with the author.
+   d. make other distribution arrangements with the author.
 
-  3. You may distribute the software in object code or executable
-     form, provided that you do at least ONE of the following:
+3. You may distribute the software in object code or executable
+   form, provided that you do at least ONE of the following:
 
-       a) distribute the executables and library files of the software,
-	  together with instructions (in the manual page or equivalent)
-	  on where to get the original distribution.
+   a. distribute the executables and library files of the software,
+      together with instructions (in the manual page or equivalent)
+      on where to get the original distribution.
 
-       b) accompany the distribution with the machine-readable source of
-	  the software.
+   b. accompany the distribution with the machine-readable source of
+      the software.
 
-       c) give non-standard executables non-standard names, with
-          instructions on where to get the original software distribution.
+   c. give non-standard executables non-standard names, with
+      instructions on where to get the original software distribution.
 
-       d) make other distribution arrangements with the author.
+   d. make other distribution arrangements with the author.
 
-  4. You may modify and include the part of the software into any other
-     software (possibly commercial).  
+4. You may modify and include the part of the software into any other
+   software (possibly commercial).
 
-  5. The scripts and library files supplied as input to or produced as 
-     output from the software do not automatically fall under the
-     copyright of the software, but belong to whomever generated them, 
-     and may be sold commercially, and may be aggregated with this
-     software.
+5. The scripts and library files supplied as input to or produced as
+   output from the software do not automatically fall under the
+   copyright of the software, but belong to whomever generated them,
+   and may be sold commercially, and may be aggregated with this
+   software.
+
+6. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
+   IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+   PURPOSE.
 
-  6. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
-     IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
-     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
-     PURPOSE.
diff --git a/lib/rubygems/available_set.rb b/lib/rubygems/available_set.rb
index bb0b3a3abe..4ab4d77716 100644
--- a/lib/rubygems/available_set.rb
+++ b/lib/rubygems/available_set.rb
@@ -116,7 +116,7 @@ class Gem::AvailableSet
 
   ##
   #
-  # Used by the DependencyResolver, the protocol to use a AvailableSet as a
+  # Used by the Resolver, the protocol to use a AvailableSet as a
   # search Set.
 
   def find_all(req)
@@ -127,7 +127,7 @@ class Gem::AvailableSet
     end
 
     match.map do |t|
-      Gem::DependencyResolver::InstalledSpecification.new(self, t.spec, t.source)
+      Gem::Resolver::InstalledSpecification.new(self, t.spec, t.source)
     end
   end
 
diff --git a/lib/rubygems/basic_specification.rb b/lib/rubygems/basic_specification.rb
index a29ed0aa6d..4f96fcac3d 100644
--- a/lib/rubygems/basic_specification.rb
+++ b/lib/rubygems/basic_specification.rb
@@ -107,7 +107,7 @@ class Gem::BasicSpecification
       File.join full_gem_path, path
     end
 
-    full_paths << extension_install_dir unless @extensions.empty?
+    full_paths.unshift extension_install_dir unless @extensions.empty?
 
     full_paths
   end
@@ -155,6 +155,10 @@ class Gem::BasicSpecification
     raise NotImplementedError
   end
 
+  def raw_require_paths # :nodoc:
+    @require_paths
+  end
+
   ##
   # Paths in the gem to add to <code>$LOAD_PATH</code> when this gem is
   # activated.
@@ -179,7 +183,7 @@ class Gem::BasicSpecification
       File.join '..', '..', 'extensions', Gem::Platform.local.to_s,
                 Gem.extension_api_version, full_name
 
-    @require_paths + [relative_extension_install_dir]
+    [relative_extension_install_dir].concat @require_paths
   end
 
   ##
diff --git a/lib/rubygems/commands/install_command.rb b/lib/rubygems/commands/install_command.rb
index ad90b37fdc..68a2fad129 100644
--- a/lib/rubygems/commands/install_command.rb
+++ b/lib/rubygems/commands/install_command.rb
@@ -56,6 +56,12 @@ class Gem::Commands::InstallCommand < Gem::Command
       o[:install_as_default] = v
     end
 
+    add_option(:"Install/Update", '--explain',
+               'Rather than install the gems, indicate which would',
+               'be installed') do |v,o|
+      o[:explain] = v
+    end
+
     @installed_specs = nil
   end
 
@@ -185,8 +191,23 @@ to write the specification by hand.  For example:
     return if options[:conservative] and
       not Gem::Dependency.new(name, version).matching_specs.empty?
 
+    req = Gem::Requirement.create(version)
+
     inst = Gem::DependencyInstaller.new options
-    inst.install name, Gem::Requirement.create(version)
+
+    if options[:explain]
+      request_set = inst.resolve_dependencies name, req
+
+      puts "Gems to install:"
+
+      request_set.specs.map { |s| s.full_name }.sort.each do |s|
+        puts "  #{s}"
+      end
+
+      return
+    else
+      inst.install name, req
+    end
 
     @installed_specs.push(*inst.installed_gems)
 
diff --git a/lib/rubygems/commands/which_command.rb b/lib/rubygems/commands/which_command.rb
index 18706afdf5..96eeb86288 100644
--- a/lib/rubygems/commands/which_command.rb
+++ b/lib/rubygems/commands/which_command.rb
@@ -35,7 +35,7 @@ requiring to see why it does not behave as you expect.
   end
 
   def execute
-    found = false
+    found = true
 
     options[:args].each do |arg|
       arg = arg.sub(/#{Regexp.union(*Gem.suffixes)}$/, '')
@@ -56,9 +56,10 @@ requiring to see why it does not behave as you expect.
 
       if paths.empty? then
         alert_error "Can't find ruby library file or shared library #{arg}"
+
+        found &&= false
       else
         say paths
-        found = true
       end
     end
 
diff --git a/lib/rubygems/dependency_installer.rb b/lib/rubygems/dependency_installer.rb
index 22ff6f5cb7..e404d42b3a 100644
--- a/lib/rubygems/dependency_installer.rb
+++ b/lib/rubygems/dependency_installer.rb
@@ -1,6 +1,5 @@
 require 'rubygems'
 require 'rubygems/dependency_list'
-require 'rubygems/dependency_resolver'
 require 'rubygems/package'
 require 'rubygems/installer'
 require 'rubygems/spec_fetcher'
@@ -196,7 +195,7 @@ class Gem::DependencyInstaller
   # sources.  Gems are sorted with newer gems preferred over older gems, and
   # local gems preferred over remote gems.
 
-  def find_gems_with_sources dep # :nodoc:
+  def find_gems_with_sources dep, best_only=false # :nodoc:
     set = Gem::AvailableSet.new
 
     if consider_local?
@@ -211,7 +210,26 @@ class Gem::DependencyInstaller
 
     if consider_remote?
       begin
-        found, errors = Gem::SpecFetcher.fetcher.spec_for_dependency dep
+        # TODO this is pulled from #spec_for_dependency to allow
+        # us to filter tuples before fetching specs.
+        #
+        tuples, errors = Gem::SpecFetcher.fetcher.search_for_dependency dep
+
+        if best_only && !tuples.empty?
+          tuples.sort! { |a,b| b[0].version <=> a[0].version }
+          tuples = [tuples.first]
+        end
+
+        specs = []
+        tuples.each do |tup, source|
+          begin
+            spec = source.fetch_spec(tup)
+          rescue Gem::RemoteFetcher::FetchError => e
+            errors << Gem::SourceFetchProblem.new(source, e)
+          else
+            specs << [spec, source]
+          end
+        end
 
         if @errors
           @errors += errors
@@ -219,7 +237,7 @@ class Gem::DependencyInstaller
           @errors = errors
         end
 
-        set << found
+        set << specs
 
       rescue Gem::RemoteFetcher::FetchError => e
         # FIX if there is a problem talking to the network, we either need to always tell
@@ -271,7 +289,7 @@ class Gem::DependencyInstaller
       dep = Gem::Dependency.new gem_name, version
       dep.prerelease = true if prerelease
 
-      set = find_gems_with_sources(dep)
+      set = find_gems_with_sources(dep, true)
       set.match_platform!
     end
 
@@ -402,7 +420,7 @@ class Gem::DependencyInstaller
     request_set = as.to_request_set install_development_deps
     request_set.soft_missing = @force
 
-    installer_set = Gem::DependencyResolver::InstallerSet.new @domain
+    installer_set = Gem::Resolver::InstallerSet.new @domain
     installer_set.always_install.concat request_set.always_install
     installer_set.ignore_installed = @only_install_dir
 
@@ -411,7 +429,7 @@ class Gem::DependencyInstaller
       request_set.soft_missing = true
     end
 
-    composed_set = Gem::DependencyResolver.compose_sets as, installer_set
+    composed_set = Gem::Resolver.compose_sets as, installer_set
 
     request_set.resolve composed_set
 
diff --git a/lib/rubygems/doctor.rb b/lib/rubygems/doctor.rb
index 0de337f7de..2cb8901b4d 100644
--- a/lib/rubygems/doctor.rb
+++ b/lib/rubygems/doctor.rb
@@ -1,6 +1,5 @@
 require 'rubygems'
 require 'rubygems/user_interaction'
-require 'pathname'
 
 ##
 # Cleans up after a partially-failed uninstall or for an invalid
@@ -39,7 +38,7 @@ class Gem::Doctor
   # If +dry_run+ is true no files or directories will be removed.
 
   def initialize gem_repository, dry_run = false
-    @gem_repository = Pathname(gem_repository)
+    @gem_repository = gem_repository
     @dry_run        = dry_run
 
     @installed_specs = nil
@@ -97,26 +96,29 @@ class Gem::Doctor
   # Removes files in +sub_directory+ with +extension+
 
   def doctor_child sub_directory, extension # :nodoc:
-    directory = @gem_repository + sub_directory
+    directory = File.join(@gem_repository, sub_directory)
 
-    directory.children.sort.each do |child|
-      next unless child.exist?
+    Dir.entries(directory).sort.each do |ent|
+      next if ent == "." || ent == ".."
 
-      basename = child.basename(extension).to_s
+      child = File.join(directory, ent)
+      next unless File.exists?(child)
+
+      basename = File.basename(child, extension)
       next if installed_specs.include? basename
       next if /^rubygems-\d/ =~ basename
       next if 'specifications' == sub_directory and 'default' == basename
 
-      type = child.directory? ? 'directory' : 'file'
+      type = File.directory?(child) ? 'directory' : 'file'
 
       action = if @dry_run then
                  'Extra'
                else
-                 child.rmtree
+                 FileUtils.rm_r(child)
                  'Removed'
                end
 
-      say "#{action} #{type} #{sub_directory}/#{child.basename}"
+      say "#{action} #{type} #{sub_directory}/#{File.basename(child)}"
     end
   rescue Errno::ENOENT
     # ignore
diff --git a/lib/rubygems/errors.rb b/lib/rubygems/errors.rb
index 3c5486a800..fc9bfbc0dc 100644
--- a/lib/rubygems/errors.rb
+++ b/lib/rubygems/errors.rb
@@ -73,12 +73,27 @@ module Gem
   # data from a source
 
   class SourceFetchProblem < ErrorReason
+
+    ##
+    # Creates a new SourceFetchProblem for the given +source+ and +error+.
+
     def initialize(source, error)
       @source = source
       @error = error
     end
 
-    attr_reader :source, :error
+    ##
+    # The source that had the fetch problem.
+
+    attr_reader :source
+
+    ##
+    # The fetch error which is an Exception subclass.
+
+    attr_reader :error
+
+    ##
+    # An English description of the error.
 
     def wordy
       "Unable to download data from #{@source.uri} - #{@error.message}"
diff --git a/lib/rubygems/exceptions.rb b/lib/rubygems/exceptions.rb
index 6d92b144b6..ee3d8fecdf 100644
--- a/lib/rubygems/exceptions.rb
+++ b/lib/rubygems/exceptions.rb
@@ -23,7 +23,7 @@ class Gem::DependencyError < Gem::Exception; end
 class Gem::DependencyRemovalException < Gem::Exception; end
 
 ##
-# Raised by Gem::DependencyResolver when a Gem::DependencyConflict reaches the
+# Raised by Gem::Resolver when a Gem::Dependency::Conflict reaches the
 # toplevel.  Indicates which dependencies were incompatible through #conflict
 # and #conflicting_dependencies
 
@@ -117,7 +117,7 @@ class Gem::SpecificGemNotFoundException < Gem::GemNotFoundException
 end
 
 ##
-# Raised by Gem::DependencyResolver when dependencies conflict and create the
+# Raised by Gem::Resolver when dependencies conflict and create the
 # inability to find a valid possible spec for a request.
 
 class Gem::ImpossibleDependenciesError < Gem::Exception
@@ -211,20 +211,20 @@ class Gem::SystemExitException < SystemExit
 end
 
 ##
-# Raised by DependencyResolver when a dependency requests a gem for which
+# Raised by Resolver when a dependency requests a gem for which
 # there is no spec.
 
 class Gem::UnsatisfiableDependencyError < Gem::Exception
 
   ##
   # The unsatisfiable dependency.  This is a
-  # Gem::DependencyResolver::DependencyRequest, not a Gem::Dependency
+  # Gem::Resolver::DependencyRequest, not a Gem::Dependency
 
   attr_reader :dependency
 
   ##
   # Creates a new UnsatisfiableDepedencyError for the unsatisfiable
-  # Gem::DependencyResolver::DependencyRequest +dep+
+  # Gem::Resolver::DependencyRequest +dep+
 
   def initialize dep, platform_mismatch=nil
     if platform_mismatch and !platform_mismatch.empty?
diff --git a/lib/rubygems/ext/builder.rb b/lib/rubygems/ext/builder.rb
index 761505636c..e9244c760c 100644
--- a/lib/rubygems/ext/builder.rb
+++ b/lib/rubygems/ext/builder.rb
@@ -149,6 +149,7 @@ EOF
     extension ||= '' # I wish I knew why this line existed
     extension_dir =
       File.expand_path File.join @gem_dir, File.dirname(extension)
+    lib_dir = File.join @spec.full_gem_path, @spec.raw_require_paths.first
 
     builder = builder_for extension
 
@@ -158,7 +159,7 @@ EOF
       CHDIR_MUTEX.synchronize do
         Dir.chdir extension_dir do
           results = builder.build(extension, @gem_dir, dest_path,
-                                  results, @build_args)
+                                  results, @build_args, lib_dir)
 
           say results.join("\n") if Gem.configuration.really_verbose
         end
diff --git a/lib/rubygems/ext/cmake_builder.rb b/lib/rubygems/ext/cmake_builder.rb
index 17bd6c296e..24531bc75c 100644
--- a/lib/rubygems/ext/cmake_builder.rb
+++ b/lib/rubygems/ext/cmake_builder.rb
@@ -1,7 +1,7 @@
 require 'rubygems/command'
 
 class Gem::Ext::CmakeBuilder < Gem::Ext::Builder
-  def self.build(extension, directory, dest_path, results)
+  def self.build(extension, directory, dest_path, results, args=[], lib_dir=nil)
     unless File.exist?('Makefile') then
       cmd = "cmake . -DCMAKE_INSTALL_PREFIX=#{dest_path}"
       cmd << " #{Gem::Command.build_args.join ' '}" unless Gem::Command.build_args.empty?
diff --git a/lib/rubygems/ext/configure_builder.rb b/lib/rubygems/ext/configure_builder.rb
index 2a542e6bd0..f66e39387a 100644
--- a/lib/rubygems/ext/configure_builder.rb
+++ b/lib/rubygems/ext/configure_builder.rb
@@ -6,7 +6,7 @@
 
 class Gem::Ext::ConfigureBuilder < Gem::Ext::Builder
 
-  def self.build(extension, directory, dest_path, results, args=[])
+  def self.build(extension, directory, dest_path, results, args=[], lib_dir=nil)
     unless File.exist?('Makefile') then
       cmd = "sh ./configure --prefix=#{dest_path}"
       cmd << " #{args.join ' '}" unless args.empty?
diff --git a/lib/rubygems/ext/ext_conf_builder.rb b/lib/rubygems/ext/ext_conf_builder.rb
index 9a656a30a3..6e736d8062 100644
--- a/lib/rubygems/ext/ext_conf_builder.rb
+++ b/lib/rubygems/ext/ext_conf_builder.rb
@@ -10,7 +10,7 @@ require 'tempfile'
 class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
   FileEntry = FileUtils::Entry_ # :nodoc:
 
-  def self.build(extension, directory, dest_path, results, args=[])
+  def self.build(extension, directory, dest_path, results, args=[], lib_dir=nil)
     tmp_dest = Dir.mktmpdir(".gem.", ".")
 
     t = nil
@@ -44,6 +44,12 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
         if tmp_dest
           FileEntry.new(tmp_dest).traverse do |ent|
+            # TODO remove in RubyGems 3
+            if lib_dir then
+              libent = ent.class.new lib_dir, ent.rel
+              libent.exist? or ent.copy libent.path
+            end
+
             destent = ent.class.new(dest_path, ent.rel)
             destent.exist? or File.rename(ent.path, destent.path)
           end
diff --git a/lib/rubygems/ext/rake_builder.rb b/lib/rubygems/ext/rake_builder.rb
index 984c54bc1b..2093bcabdd 100644
--- a/lib/rubygems/ext/rake_builder.rb
+++ b/lib/rubygems/ext/rake_builder.rb
@@ -6,7 +6,7 @@
 
 class Gem::Ext::RakeBuilder < Gem::Ext::Builder
 
-  def self.build(extension, directory, dest_path, results, args=[])
+  def self.build(extension, directory, dest_path, results, args=[], lib_dir=nil)
     if File.basename(extension) =~ /mkrf_conf/i then
       cmd = "#{Gem.ruby} #{File.basename extension}"
       cmd << " #{args.join " "}" unless args.empty?
diff --git a/lib/rubygems/remote_fetcher.rb b/lib/rubygems/remote_fetcher.rb
index b96c77033a..c6816e8f0f 100644
--- a/lib/rubygems/remote_fetcher.rb
+++ b/lib/rubygems/remote_fetcher.rb
@@ -90,7 +90,7 @@ class Gem::RemoteFetcher
     rescue Resolv::ResolvError
       uri
     else
-      URI.parse "#{res.target}#{uri.path}"
+      URI.parse "#{uri.scheme}://#{res.target}#{uri.path}"
     end
   end
 
diff --git a/lib/rubygems/request_set.rb b/lib/rubygems/request_set.rb
index 3a997f32ee..42d457063f 100644
--- a/lib/rubygems/request_set.rb
+++ b/lib/rubygems/request_set.rb
@@ -1,6 +1,5 @@
 require 'rubygems'
 require 'rubygems/dependency'
-require 'rubygems/dependency_resolver'
 require 'rubygems/dependency_list'
 require 'rubygems/installer'
 require 'tsort'
@@ -32,6 +31,11 @@ class Gem::RequestSet
   attr_accessor :development
 
   ##
+  # The set of git gems imported via load_gemdeps.
+
+  attr_reader :git_set # :nodoc:
+
+  ##
   # Sets used for resolution
 
   attr_reader :sets # :nodoc:
@@ -61,6 +65,7 @@ class Gem::RequestSet
     @always_install   = []
     @dependency_names = {}
     @development      = false
+    @git_set          = nil
     @requests         = []
     @sets             = []
     @soft_missing     = false
@@ -184,7 +189,8 @@ class Gem::RequestSet
   # Load a dependency management file.
 
   def load_gemdeps path, without_groups = []
-    @vendor_set = Gem::DependencyResolver::VendorSet.new
+    @git_set    = Gem::Resolver::GitSet.new
+    @vendor_set = Gem::Resolver::VendorSet.new
 
     gf = Gem::RequestSet::GemDependencyAPI.new self, path
     gf.without_groups = without_groups if without_groups
@@ -195,13 +201,14 @@ class Gem::RequestSet
   # Resolve the requested dependencies and return an Array of Specification
   # objects to be activated.
 
-  def resolve set = Gem::DependencyResolver::IndexSet.new
+  def resolve set = Gem::Resolver::IndexSet.new
     @sets << set
+    @sets << @git_set
     @sets << @vendor_set
 
-    set = Gem::DependencyResolver.compose_sets(*@sets)
+    set = Gem::Resolver.compose_sets(*@sets)
 
-    resolver = Gem::DependencyResolver.new @dependencies, set
+    resolver = Gem::Resolver.new @dependencies, set
     resolver.development  = @development
     resolver.soft_missing = @soft_missing
 
@@ -213,7 +220,7 @@ class Gem::RequestSet
   # and return an Array of Specification objects to be activated.
 
   def resolve_current
-    resolve Gem::DependencyResolver::CurrentSet.new
+    resolve Gem::Resolver::CurrentSet.new
   end
 
   def sorted_requests
diff --git a/lib/rubygems/request_set/gem_dependency_api.rb b/lib/rubygems/request_set/gem_dependency_api.rb
index e8f3138990..8e29eb87e5 100644
--- a/lib/rubygems/request_set/gem_dependency_api.rb
+++ b/lib/rubygems/request_set/gem_dependency_api.rb
@@ -108,6 +108,11 @@ class Gem::RequestSet::GemDependencyAPI
   }
 
   ##
+  # A set of gems that are loaded via the +:git+ option to #gem
+
+  attr_reader :git_set # :nodoc:
+
+  ##
   # A Hash containing gem names and files to require from those gems.
 
   attr_reader :requires
@@ -130,13 +135,55 @@ class Gem::RequestSet::GemDependencyAPI
     @set = set
     @path = path
 
-    @current_groups   = nil
-    @current_platform = nil
-    @default_sources  = true
-    @requires         = Hash.new { |h, name| h[name] = [] }
-    @vendor_set       = @set.vendor_set
-    @gem_sources      = {}
-    @without_groups   = []
+    @current_groups     = nil
+    @current_platform   = nil
+    @current_repository = nil
+    @default_sources    = true
+    @git_set            = @set.git_set
+    @requires           = Hash.new { |h, name| h[name] = [] }
+    @vendor_set         = @set.vendor_set
+    @gem_sources        = {}
+    @without_groups     = []
+  end
+
+  ##
+  # Adds +dependencies+ to the request set if any of the +groups+ are allowed.
+  # This is used for gemspec dependencies.
+
+  def add_dependencies groups, dependencies # :nodoc:
+    return unless (groups & @without_groups).empty?
+
+    dependencies.each do |dep|
+      @set.gem dep.name, *dep.requirement
+    end
+  end
+
+  private :add_dependencies
+
+  ##
+  # Finds a gemspec with the given +name+ that lives at +path+.
+
+  def find_gemspec name, path # :nodoc:
+    glob = File.join path, "#{name}.gemspec"
+
+    spec_files = Dir[glob]
+
+    case spec_files.length
+    when 1 then
+      spec_file = spec_files.first
+
+      spec = Gem::Specification.load spec_file
+
+      return spec if spec
+
+      raise ArgumentError, "invalid gemspec #{spec_file}"
+    when 0 then
+      raise ArgumentError, "no gemspecs found at #{Dir.pwd}"
+    else
+      raise ArgumentError,
+        "found multiple gemspecs at #{Dir.pwd}, " +
+        "use the name: option to specify the one you want"
+    end
   end
 
   ##
@@ -160,7 +207,13 @@ class Gem::RequestSet::GemDependencyAPI
     options = requirements.pop if requirements.last.kind_of?(Hash)
     options ||= {}
 
-    source_set = gem_path name, options
+    options[:git] = @current_repository if @current_repository
+
+    source_set = false
+
+    source_set ||= gem_path   name, options
+    source_set ||= gem_git    name, options
+    source_set ||= gem_github name, options
 
     return unless gem_platforms options
 
@@ -182,6 +235,54 @@ class Gem::RequestSet::GemDependencyAPI
   end
 
   ##
+  # Handles the git: option from +options+ for gem +name+.
+  #
+  # Returns +true+ if the path option was handled.
+
+  def gem_git name, options # :nodoc:
+    if gist = options.delete(:gist) then
+      options[:git] = "https://gist.github.com/#{gist}.git"
+    end
+
+    return unless repository = options.delete(:git)
+
+    raise ArgumentError,
+      "duplicate source git: #{repository} for gem #{name}" if
+        @gem_sources.include? name
+
+    reference = nil
+    reference ||= options.delete :ref
+    reference ||= options.delete :branch
+    reference ||= options.delete :tag
+    reference ||= 'master'
+
+    submodules = options.delete :submodules
+
+    @git_set.add_git_gem name, repository, reference, submodules
+
+    @gem_sources[name] = repository
+
+    true
+  end
+
+  private :gem_git
+
+  ##
+  # Handles the github: option from +options+ for gem +name+.
+  #
+  # Returns +true+ if the path option was handled.
+
+  def gem_github name, options # :nodoc:
+    return unless path = options.delete(:github)
+
+    options[:git] = "git://github.com/#{path}.git"
+
+    gem_git name, options
+
+    true
+  end
+
+  ##
   # Handles the :group and :groups +options+ for the gem with the given
   # +name+.
 
@@ -269,6 +370,15 @@ class Gem::RequestSet::GemDependencyAPI
 
   private :gem_requires
 
+  def git repository
+    @current_repository = repository
+
+    yield
+
+  ensure
+    @current_repository = nil
+  end
+
   ##
   # Returns the basename of the file the dependencies were loaded from
 
@@ -278,6 +388,29 @@ class Gem::RequestSet::GemDependencyAPI
 
   ##
   # :category: Gem Dependencies DSL
+  #
+  # Loads dependencies from a gemspec file.
+
+  def gemspec options = {}
+    name              = options.delete(:name) || '{,*}'
+    path              = options.delete(:path) || '.'
+    development_group = options.delete(:development_group) || :development
+
+    spec = find_gemspec name, path
+
+    groups = gem_group spec.name, {}
+
+    add_dependencies groups, spec.runtime_dependencies
+
+    groups << development_group
+
+    add_dependencies groups, spec.development_dependencies
+
+    gem_requires spec.name, options
+  end
+
+  ##
+  # :category: Gem Dependencies DSL
   # Block form for placing a dependency in the given +groups+.
 
   def group *groups
diff --git a/lib/rubygems/request_set/lockfile.rb b/lib/rubygems/request_set/lockfile.rb
index a9c419549d..0073bfdcc5 100644
--- a/lib/rubygems/request_set/lockfile.rb
+++ b/lib/rubygems/request_set/lockfile.rb
@@ -1,5 +1,3 @@
-require 'pathname'
-
 class Gem::RequestSet::Lockfile
 
   ##
@@ -46,8 +44,8 @@ class Gem::RequestSet::Lockfile
 
   def initialize request_set, gem_deps_file
     @set           = request_set
-    @gem_deps_file = Pathname(gem_deps_file).expand_path
-    @gem_deps_dir  = @gem_deps_file.dirname
+    @gem_deps_file = File.expand_path(gem_deps_file)
+    @gem_deps_dir  = File.dirname(@gem_deps_file)
 
     @current_token  = nil
     @line           = 0
@@ -62,7 +60,7 @@ class Gem::RequestSet::Lockfile
     @set.dependencies.sort.map do |dependency|
       source = @requests.find do |req|
         req.name == dependency.name and
-          req.spec.class == Gem::DependencyResolver::VendorSpecification
+          req.spec.class == Gem::Resolver::VendorSpecification
       end
 
       source_dep = '!' if source
@@ -102,15 +100,26 @@ class Gem::RequestSet::Lockfile
     out << nil
   end
 
+  def relative_path_from(dest, base)
+    dest = File.expand_path(dest)
+    base = File.expand_path(base)
+
+    if dest.index(base) == 0
+      return dest[base.size+1..-1]
+    else
+      dest
+    end
+  end
+
   def add_PATH out # :nodoc:
     return unless path_requests =
-      @spec_groups.delete(Gem::DependencyResolver::VendorSpecification)
+      @spec_groups.delete(Gem::Resolver::VendorSpecification)
 
     out << "PATH"
     path_requests.each do |request|
-      directory = Pathname(request.spec.source.uri).expand_path
+      directory = File.expand_path(request.spec.source.uri)
 
-      out << "  remote: #{directory.relative_path_from @gem_deps_dir}"
+      out << "  remote: #{relative_path_from directory, @gem_deps_dir}"
       out << "  specs:"
       out << "    #{request.name} (#{request.version})"
     end
@@ -208,7 +217,7 @@ class Gem::RequestSet::Lockfile
 
     skip :newline
 
-    set = Gem::DependencyResolver::LockSet.new source
+    set = Gem::Resolver::LockSet.new source
 
     while not @tokens.empty? and :text == peek.first do
       _, name, = get :text
diff --git a/lib/rubygems/dependency_resolver.rb b/lib/rubygems/resolver.rb
index 35fbe925ad..2669cc4f24 100644
--- a/lib/rubygems/dependency_resolver.rb
+++ b/lib/rubygems/resolver.rb
@@ -12,7 +12,7 @@ require 'net/http'
 # objects which indicate all the specs that should be activated to meet the
 # all the requirements.
 
-class Gem::DependencyResolver
+class Gem::Resolver
 
   ##
   # Contains all the conflicts encountered while doing resolution
@@ -38,20 +38,20 @@ class Gem::DependencyResolver
     when 1 then
       sets.first
     else
-      Gem::DependencyResolver::ComposedSet.new(*sets)
+      Gem::Resolver::ComposedSet.new(*sets)
     end
   end
 
   ##
-  # Provide a DependencyResolver that queries only against the already
+  # Provide a Resolver that queries only against the already
   # installed gems.
 
   def self.for_current_gems needed
-    new needed, Gem::DependencyResolver::CurrentSet.new
+    new needed, Gem::Resolver::CurrentSet.new
   end
 
   ##
-  # Create DependencyResolver object which will resolve the tree starting
+  # Create Resolver object which will resolve the tree starting
   # with +needed+ Dependency objects.
   #
   # +set+ is an object that provides where to look for specifications to
@@ -59,7 +59,7 @@ class Gem::DependencyResolver
   # rubygems.org.
 
   def initialize needed, set = nil
-    @set = set || Gem::DependencyResolver::IndexSet.new
+    @set = set || Gem::Resolver::IndexSet.new
     @needed = needed
 
     @conflicts    = []
@@ -68,6 +68,15 @@ class Gem::DependencyResolver
     @soft_missing = false
   end
 
+  DEBUG_RESOLVER = !ENV['DEBUG_RESOLVER'].nil?
+
+  def explain(stage, *data)
+    if DEBUG_RESOLVER
+      d = data.map { |x| x.inspect }.join(", ")
+      STDOUT.printf "%20s %s\n", stage.to_s.upcase, d
+    end
+  end
+
   ##
   # Creates an ActivationRequest for the given +dep+ and the last +possible+
   # specification.
@@ -77,8 +86,10 @@ class Gem::DependencyResolver
   def activation_request dep, possible # :nodoc:
     spec = possible.pop
 
+    explain :activate, [spec.full_name, possible.size]
+
     activation_request =
-      Gem::DependencyResolver::ActivationRequest.new spec, dep, possible
+      Gem::Resolver::ActivationRequest.new spec, dep, possible
 
     return spec, activation_request
   end
@@ -86,7 +97,7 @@ class Gem::DependencyResolver
   def requests s, act, reqs=nil
     s.dependencies.reverse_each do |d|
       next if d.type == :development and not @development
-      reqs = Gem::List.new Gem::DependencyResolver::DependencyRequest.new(d, act), reqs
+      reqs.add Gem::Resolver::DependencyRequest.new(d, act)
     end
 
     @set.prefetch reqs
@@ -100,18 +111,18 @@ class Gem::DependencyResolver
   def resolve
     @conflicts = []
 
-    needed = nil
+    needed = RequirementList.new
 
     @needed.reverse_each do |n|
-      request = Gem::DependencyResolver::DependencyRequest.new n, nil
+      request = Gem::Resolver::DependencyRequest.new n, nil
 
-      needed = Gem::List.new request, needed
+      needed.add request
     end
 
     res = resolve_for needed, nil
 
     raise Gem::DependencyResolutionError, res if
-      res.kind_of? Gem::DependencyResolver::DependencyConflict
+      res.kind_of? Gem::Resolver::Conflict
 
     res.to_a
   end
@@ -128,6 +139,8 @@ class Gem::DependencyResolver
     until states.empty? do
       state = states.pop
 
+      explain :consider, state.dep, conflict.failed_dep
+
       if conflict.for_spec? state.spec
         state.conflicts << [state.spec, conflict]
         return state
@@ -162,11 +175,11 @@ class Gem::DependencyResolver
     # Otherwise, issue it on the requester's request itself.
     if existing.others_possible? or existing.request.requester.nil? then
       conflict =
-        Gem::DependencyResolver::DependencyConflict.new dep, existing
+        Gem::Resolver::Conflict.new dep, existing
     else
-      depreq = existing.request.requester.request
+      depreq = dep.requester.request
       conflict =
-        Gem::DependencyResolver::DependencyConflict.new depreq, existing, dep
+        Gem::Resolver::Conflict.new depreq, existing, dep
     end
 
     @conflicts << conflict unless @conflicts.include? conflict
@@ -182,7 +195,7 @@ class Gem::DependencyResolver
   # +spec+ is the Specification for this state.
   # +possible+ is List of DependencyRequest objects that can be tried to
   # find a  complete set.
-  # +conflicts+ is a [DependencyRequest, DependencyConflict] hit tried to
+  # +conflicts+ is a [DependencyRequest, Conflict] hit tried to
   # activate the state.
   #
   State = Struct.new(:needed, :specs, :dep, :spec, :possibles, :conflicts) do
@@ -218,9 +231,9 @@ class Gem::DependencyResolver
     # The State objects that are used to attempt the activation tree.
     states = []
 
-    while needed
-      dep = needed.value
-      needed = needed.tail
+    while !needed.empty?
+      dep = needed.remove
+      explain :try, [dep, dep.requester ? dep.requester.request : :toplevel]
 
       # If there is already a spec activated for the requested name...
       if specs && existing = specs.find { |s| dep.name == s.name }
@@ -228,6 +241,7 @@ class Gem::DependencyResolver
         next if dep.matches_spec? existing
 
         conflict = handle_conflict dep, existing
+        explain :conflict, conflict.explain
 
         state = find_conflict_state conflict, states
 
@@ -292,7 +306,9 @@ class Gem::DependencyResolver
     # We may need to try all of +possible+, so we setup state to unwind back
     # to current +needed+ and +specs+ so we can try another. This is code is
     # what makes conflict resolution possible.
-    states << State.new(needed, specs, dep, spec, possible, [])
+    states << State.new(needed.dup, specs, dep, spec, possible, [])
+
+    explain :states, states.map { |s| s.dep }
 
     needed = requests spec, act, needed
     specs = Gem::List.prepend specs, act
@@ -341,24 +357,32 @@ class Gem::DependencyResolver
 
 end
 
-require 'rubygems/dependency_resolver/activation_request'
-require 'rubygems/dependency_resolver/dependency_conflict'
-require 'rubygems/dependency_resolver/dependency_request'
-
-require 'rubygems/dependency_resolver/set'
-require 'rubygems/dependency_resolver/api_set'
-require 'rubygems/dependency_resolver/composed_set'
-require 'rubygems/dependency_resolver/best_set'
-require 'rubygems/dependency_resolver/current_set'
-require 'rubygems/dependency_resolver/index_set'
-require 'rubygems/dependency_resolver/installer_set'
-require 'rubygems/dependency_resolver/lock_set'
-require 'rubygems/dependency_resolver/vendor_set'
-
-require 'rubygems/dependency_resolver/specification'
-require 'rubygems/dependency_resolver/spec_specification'
-require 'rubygems/dependency_resolver/api_specification'
-require 'rubygems/dependency_resolver/index_specification'
-require 'rubygems/dependency_resolver/installed_specification'
-require 'rubygems/dependency_resolver/vendor_specification'
+##
+# TODO remove in RubyGems 3
+
+Gem::DependencyResolver = Gem::Resolver # :nodoc:
+
+require 'rubygems/resolver/activation_request'
+require 'rubygems/resolver/conflict'
+require 'rubygems/resolver/dependency_request'
+require 'rubygems/resolver/requirement_list'
+
+require 'rubygems/resolver/set'
+require 'rubygems/resolver/api_set'
+require 'rubygems/resolver/composed_set'
+require 'rubygems/resolver/best_set'
+require 'rubygems/resolver/current_set'
+require 'rubygems/resolver/git_set'
+require 'rubygems/resolver/index_set'
+require 'rubygems/resolver/installer_set'
+require 'rubygems/resolver/lock_set'
+require 'rubygems/resolver/vendor_set'
+
+require 'rubygems/resolver/specification'
+require 'rubygems/resolver/spec_specification'
+require 'rubygems/resolver/api_specification'
+require 'rubygems/resolver/git_specification'
+require 'rubygems/resolver/index_specification'
+require 'rubygems/resolver/installed_specification'
+require 'rubygems/resolver/vendor_specification'
 
diff --git a/lib/rubygems/dependency_resolver/activation_request.rb b/lib/rubygems/resolver/activation_request.rb
index c5d1e24d85..ca82ac408a 100644
--- a/lib/rubygems/dependency_resolver/activation_request.rb
+++ b/lib/rubygems/resolver/activation_request.rb
@@ -3,7 +3,7 @@
 # Also contains a dependency that was used to introduce this
 # activation.
 
-class Gem::DependencyResolver::ActivationRequest
+class Gem::Resolver::ActivationRequest
 
   attr_reader :request
 
@@ -19,7 +19,7 @@ class Gem::DependencyResolver::ActivationRequest
     case other
     when Gem::Specification
       @spec == other
-    when Gem::DependencyResolver::ActivationRequest
+    when Gem::Resolver::ActivationRequest
       @spec == other.spec && @request == other.request
     else
       false
@@ -70,7 +70,7 @@ class Gem::DependencyResolver::ActivationRequest
 
   def installed?
     case @spec
-    when Gem::DependencyResolver::VendorSpecification then
+    when Gem::Resolver::VendorSpecification then
       true
     else
       this_spec = full_spec
diff --git a/lib/rubygems/dependency_resolver/api_set.rb b/lib/rubygems/resolver/api_set.rb
index 9dd34562b1..60bf911063 100644
--- a/lib/rubygems/dependency_resolver/api_set.rb
+++ b/lib/rubygems/resolver/api_set.rb
@@ -2,7 +2,7 @@
 # The global rubygems pool, available via the rubygems.org API.
 # Returns instances of APISpecification.
 
-class Gem::DependencyResolver::APISet < Gem::DependencyResolver::Set
+class Gem::Resolver::APISet < Gem::Resolver::Set
 
   ##
   # The URI for the dependency API this APISet uses.
@@ -28,7 +28,7 @@ class Gem::DependencyResolver::APISet < Gem::DependencyResolver::Set
 
     versions(req.name).each do |ver|
       if req.dependency.match? req.name, ver[:number]
-        res << Gem::DependencyResolver::APISpecification.new(self, ver)
+        res << Gem::Resolver::APISpecification.new(self, ver)
       end
     end
 
diff --git a/lib/rubygems/dependency_resolver/api_specification.rb b/lib/rubygems/resolver/api_specification.rb
index 5178d7c28e..19611e17d8 100644
--- a/lib/rubygems/dependency_resolver/api_specification.rb
+++ b/lib/rubygems/resolver/api_specification.rb
@@ -4,7 +4,7 @@
 # This is used to avoid loading the full Specification object when all we need
 # is the name, version, and dependencies.
 
-class Gem::DependencyResolver::APISpecification < Gem::DependencyResolver::Specification
+class Gem::Resolver::APISpecification < Gem::Resolver::Specification
 
   ##
   # Creates an APISpecification for the given +set+ from the rubygems.org
diff --git a/lib/rubygems/dependency_resolver/best_set.rb b/lib/rubygems/resolver/best_set.rb
index 987eea552e..533a0db58f 100644
--- a/lib/rubygems/dependency_resolver/best_set.rb
+++ b/lib/rubygems/resolver/best_set.rb
@@ -3,7 +3,7 @@
 #
 # It combines IndexSet and APISet
 
-class Gem::DependencyResolver::BestSet < Gem::DependencyResolver::ComposedSet
+class Gem::Resolver::BestSet < Gem::Resolver::ComposedSet
 
   ##
   # Creates a BestSet for the given +sources+ or Gem::sources if none are
diff --git a/lib/rubygems/dependency_resolver/composed_set.rb b/lib/rubygems/resolver/composed_set.rb
index aeecf047b8..e4aa15e4d0 100644
--- a/lib/rubygems/dependency_resolver/composed_set.rb
+++ b/lib/rubygems/resolver/composed_set.rb
@@ -1,4 +1,4 @@
-class Gem::DependencyResolver::ComposedSet < Gem::DependencyResolver::Set
+class Gem::Resolver::ComposedSet < Gem::Resolver::Set
 
   attr_reader :sets # :nodoc:
 
diff --git a/lib/rubygems/dependency_resolver/dependency_conflict.rb b/lib/rubygems/resolver/conflict.rb
index 092f000cdb..b081972658 100644
--- a/lib/rubygems/dependency_resolver/dependency_conflict.rb
+++ b/lib/rubygems/resolver/conflict.rb
@@ -2,7 +2,7 @@
 # Used internally to indicate that a dependency conflicted
 # with a spec that would be activated.
 
-class Gem::DependencyResolver::DependencyConflict
+class Gem::Resolver::Conflict
 
   attr_reader :activated
 
@@ -23,6 +23,10 @@ class Gem::DependencyResolver::DependencyConflict
       @failed_dep == other.failed_dep
   end
 
+  def explain
+    "<Conflict wanted: #{@failed_dep}, had: #{activated.spec.full_name}>"
+  end
+
   ##
   # Return the 2 dependency objects that conflicted
 
@@ -94,3 +98,5 @@ class Gem::DependencyResolver::DependencyConflict
 
 end
 
+Gem::Resolver::DependencyConflict = Gem::Resolver::Conflict
+
diff --git a/lib/rubygems/dependency_resolver/current_set.rb b/lib/rubygems/resolver/current_set.rb
index ef15c9d7f3..4e8d34026b 100644
--- a/lib/rubygems/dependency_resolver/current_set.rb
+++ b/lib/rubygems/resolver/current_set.rb
@@ -3,7 +3,7 @@
 # all the normal settings that control where to look
 # for installed gems.
 
-class Gem::DependencyResolver::CurrentSet < Gem::DependencyResolver::Set
+class Gem::Resolver::CurrentSet < Gem::Resolver::Set
 
   def find_all req
     req.dependency.matching_specs
diff --git a/lib/rubygems/dependency_resolver/dependency_request.rb b/lib/rubygems/resolver/dependency_request.rb
index 36b77ab558..e63b443c62 100644
--- a/lib/rubygems/dependency_resolver/dependency_request.rb
+++ b/lib/rubygems/resolver/dependency_request.rb
@@ -2,7 +2,7 @@
 # Used Internally. Wraps a Dependency object to also track which spec
 # contained the Dependency.
 
-class Gem::DependencyResolver::DependencyRequest
+class Gem::Resolver::DependencyRequest
 
   attr_reader :dependency
 
@@ -17,7 +17,7 @@ class Gem::DependencyResolver::DependencyRequest
     case other
     when Gem::Dependency
       @dependency == other
-    when Gem::DependencyResolver::DependencyRequest
+    when Gem::Resolver::DependencyRequest
       @dependency == other.dependency && @requester == other.requester
     else
       false
diff --git a/lib/rubygems/resolver/git_set.rb b/lib/rubygems/resolver/git_set.rb
new file mode 100644
index 0000000000..3c38d3dca0
--- /dev/null
+++ b/lib/rubygems/resolver/git_set.rb
@@ -0,0 +1,81 @@
+##
+# A GitSet represents gems that are sourced from git repositories.
+#
+# This is used for gem dependency file support.
+#
+# Example:
+#
+#   set = Gem::Resolver::GitSet.new
+#   set.add_git_gem 'rake', 'git://example/rake.git', tag: 'rake-10.1.0'
+
+class Gem::Resolver::GitSet < Gem::Resolver::Set
+
+  ##
+  # Contains repositories needing submodules
+
+  attr_reader :need_submodules # :nodoc:
+
+  ##
+  # A Hash containing git gem names for keys and a Hash of repository and
+  # git commit reference as values.
+
+  attr_reader :repositories # :nodoc:
+
+  ##
+  # A hash of gem names to Gem::Resolver::GitSpecifications
+
+  attr_reader :specs # :nodoc:
+
+  def initialize # :nodoc:
+    @git             = ENV['git'] || 'git'
+    @need_submodules = {}
+    @repositories    = {}
+    @specs           = {}
+  end
+
+  def add_git_gem name, repository, reference, submodules # :nodoc:
+    @repositories[name] = [repository, reference]
+    @need_submodules[repository] = submodules
+  end
+
+  ##
+  # Finds all git gems matching +req+
+
+  def find_all req
+    @repositories.keys.select do |name|
+      name == req.name
+    end.map do |name|
+      @specs[name] || load_spec(name)
+    end.select do |spec|
+      req.matches_spec? spec
+    end
+  end
+
+  def load_spec name
+    repository, reference = @repositories[name]
+
+    source = Gem::Source::Git.new name, repository, reference
+
+    spec = source.load_spec name
+
+    git_spec =
+      Gem::Resolver::GitSpecification.new self, spec, source
+
+    @specs[name] = git_spec
+  end
+
+  ##
+  # Prefetches specifications from the git repositories in this set.
+
+  def prefetch reqs
+    names = reqs.map { |req| req.name }
+
+    @repositories.each_key do |name|
+      next unless names.include? name
+
+      load_spec name
+    end
+  end
+
+end
+
diff --git a/lib/rubygems/resolver/git_specification.rb b/lib/rubygems/resolver/git_specification.rb
new file mode 100644
index 0000000000..ac8d4e9aeb
--- /dev/null
+++ b/lib/rubygems/resolver/git_specification.rb
@@ -0,0 +1,16 @@
+##
+# A GitSpecification represents a gem that is sourced from a git repository
+# and is being loaded through a gem dependencies file through the +git:+
+# option.
+
+class Gem::Resolver::GitSpecification < Gem::Resolver::SpecSpecification
+
+  def == other # :nodoc:
+    self.class === other and
+      @set  == other.set and
+      @spec == other.spec and
+      @source == other.source
+  end
+
+end
+
diff --git a/lib/rubygems/dependency_resolver/index_set.rb b/lib/rubygems/resolver/index_set.rb
index 04d6ec816f..0ba3c78a44 100644
--- a/lib/rubygems/dependency_resolver/index_set.rb
+++ b/lib/rubygems/resolver/index_set.rb
@@ -2,7 +2,7 @@
 # The global rubygems pool represented via the traditional
 # source index.
 
-class Gem::DependencyResolver::IndexSet < Gem::DependencyResolver::Set
+class Gem::Resolver::IndexSet < Gem::Resolver::Set
 
   def initialize source = nil # :nodoc:
     @f =
@@ -38,7 +38,7 @@ class Gem::DependencyResolver::IndexSet < Gem::DependencyResolver::Set
 
     @all[name].each do |uri, n|
       if req.dependency.match? n then
-        res << Gem::DependencyResolver::IndexSpecification.new(
+        res << Gem::Resolver::IndexSpecification.new(
           self, n.name, n.version, uri, n.platform)
       end
     end
diff --git a/lib/rubygems/dependency_resolver/index_specification.rb b/lib/rubygems/resolver/index_specification.rb
index 9b4057f0c8..56fecb5753 100644
--- a/lib/rubygems/dependency_resolver/index_specification.rb
+++ b/lib/rubygems/resolver/index_specification.rb
@@ -3,7 +3,7 @@
 # delay needed to download full Specification objects when only the +name+
 # and +version+ are needed.
 
-class Gem::DependencyResolver::IndexSpecification < Gem::DependencyResolver::Specification
+class Gem::Resolver::IndexSpecification < Gem::Resolver::Specification
 
   ##
   # An IndexSpecification is created from the index format described in `gem
diff --git a/lib/rubygems/dependency_resolver/installed_specification.rb b/lib/rubygems/resolver/installed_specification.rb
index 4b591661a8..647ff7499a 100644
--- a/lib/rubygems/dependency_resolver/installed_specification.rb
+++ b/lib/rubygems/resolver/installed_specification.rb
@@ -2,7 +2,7 @@
 # An InstalledSpecification represents a gem that is already installed
 # locally.
 
-class Gem::DependencyResolver::InstalledSpecification < Gem::DependencyResolver::SpecSpecification
+class Gem::Resolver::InstalledSpecification < Gem::Resolver::SpecSpecification
 
   def == other # :nodoc:
     self.class === other and
diff --git a/lib/rubygems/dependency_resolver/installer_set.rb b/lib/rubygems/resolver/installer_set.rb
index 801b60a8bb..73d9e39651 100644
--- a/lib/rubygems/dependency_resolver/installer_set.rb
+++ b/lib/rubygems/resolver/installer_set.rb
@@ -2,7 +2,7 @@
 # A set of gems for installation sourced from remote sources and local .gem
 # files
 
-class Gem::DependencyResolver::InstallerSet < Gem::DependencyResolver::Set
+class Gem::Resolver::InstallerSet < Gem::Resolver::Set
 
   ##
   # List of Gem::Specification objects that must always be installed.
@@ -64,14 +64,14 @@ class Gem::DependencyResolver::InstallerSet < Gem::DependencyResolver::Set
     dep.matching_specs.each do |gemspec|
       next if @always_install.include? gemspec
 
-      res << Gem::DependencyResolver::InstalledSpecification.new(self, gemspec)
+      res << Gem::Resolver::InstalledSpecification.new(self, gemspec)
     end unless @ignore_installed
 
     if consider_local? then
       local_source = Gem::Source::Local.new
 
       if spec = local_source.find_gem(name, dep.requirement) then
-        res << Gem::DependencyResolver::IndexSpecification.new(
+        res << Gem::Resolver::IndexSpecification.new(
           self, spec.name, spec.version, local_source, spec.platform)
       end
     end
@@ -81,7 +81,7 @@ class Gem::DependencyResolver::InstallerSet < Gem::DependencyResolver::Set
 
       @all[name].each do |remote_source, n|
         if dep.match? n then
-          res << Gem::DependencyResolver::IndexSpecification.new(
+          res << Gem::Resolver::IndexSpecification.new(
             self, n.name, n.version, remote_source, n.platform)
         end
       end
diff --git a/lib/rubygems/dependency_resolver/lock_set.rb b/lib/rubygems/resolver/lock_set.rb
index f95c7f0fd6..6885e70945 100644
--- a/lib/rubygems/dependency_resolver/lock_set.rb
+++ b/lib/rubygems/resolver/lock_set.rb
@@ -1,7 +1,7 @@
 ##
 # A set of gems from a gem dependencies lockfile.
 
-class Gem::DependencyResolver::LockSet < Gem::DependencyResolver::Set
+class Gem::Resolver::LockSet < Gem::Resolver::Set
 
   attr_reader :specs # :nodoc:
 
@@ -24,8 +24,8 @@ class Gem::DependencyResolver::LockSet < Gem::DependencyResolver::Set
     version = Gem::Version.new version
 
     spec =
-      Gem::DependencyResolver::IndexSpecification.new self, name, version,
-                                                      @source, platform
+      Gem::Resolver::IndexSpecification.new self, name, version, @source,
+                                            platform
 
     @specs << spec
   end
diff --git a/lib/rubygems/resolver/requirement_list.rb b/lib/rubygems/resolver/requirement_list.rb
new file mode 100644
index 0000000000..8123e84fc7
--- /dev/null
+++ b/lib/rubygems/resolver/requirement_list.rb
@@ -0,0 +1,40 @@
+##
+# Used internally to hold the requirements being considered
+# while attempting to find a proper activation set.
+
+class Gem::Resolver::RequirementList
+
+  include Enumerable
+
+  def initialize
+    @list = []
+  end
+
+  def initialize_copy(other)
+    @list = @list.dup
+  end
+
+  def add(req)
+    @list.push req
+    req
+  end
+
+  ##
+  # Enumerates requirements in the list
+
+  def each # :nodoc:
+    return enum_for __method__ unless block_given?
+
+    @list.each do |requirement|
+      yield requirement
+    end
+  end
+
+  def empty?
+    @list.empty?
+  end
+
+  def remove
+    @list.shift
+  end
+end
diff --git a/lib/rubygems/dependency_resolver/set.rb b/lib/rubygems/resolver/set.rb
index 65801871ac..32c137ef6b 100644
--- a/lib/rubygems/dependency_resolver/set.rb
+++ b/lib/rubygems/resolver/set.rb
@@ -1,13 +1,12 @@
 ##
-# DependencyResolver sets are used to look up specifications (and their
+# Resolver sets are used to look up specifications (and their
 # dependencies) used in resolution.  This set is abstract.
 
-class Gem::DependencyResolver::Set
+class Gem::Resolver::Set
 
   ##
-  # The find_all method must be implemented.  It returns all
-  # DependencyResolver Specification objects matching the given
-  # DependencyRequest +req+.
+  # The find_all method must be implemented.  It returns all Resolver
+  # Specification objects matching the given DependencyRequest +req+.
 
   def find_all req
     raise NotImplementedError
diff --git a/lib/rubygems/dependency_resolver/spec_specification.rb b/lib/rubygems/resolver/spec_specification.rb
index cca1d58b9f..0c411bdf5f 100644
--- a/lib/rubygems/dependency_resolver/spec_specification.rb
+++ b/lib/rubygems/resolver/spec_specification.rb
@@ -1,8 +1,8 @@
 ##
-# The DependencyResolver::SpecSpecification contains common functionality for
-# DependencyResolver specifications that are backed by a Gem::Specification.
+# The Resolver::SpecSpecification contains common functionality for
+# Resolver specifications that are backed by a Gem::Specification.
 
-class Gem::DependencyResolver::SpecSpecification < Gem::DependencyResolver::Specification
+class Gem::Resolver::SpecSpecification < Gem::Resolver::Specification
 
   attr_reader :spec # :nodoc:
 
diff --git a/lib/rubygems/dependency_resolver/specification.rb b/lib/rubygems/resolver/specification.rb
index 6fbd241316..7dd4c2e829 100644
--- a/lib/rubygems/dependency_resolver/specification.rb
+++ b/lib/rubygems/resolver/specification.rb
@@ -1,9 +1,9 @@
 ##
-# A DependencyResolver::Specification contains a subset of the information
+# A Resolver::Specification contains a subset of the information
 # contained in a Gem::Specification.  Only the information necessary for
 # dependency resolution in the resolver is included.
 
-class Gem::DependencyResolver::Specification
+class Gem::Resolver::Specification
 
   ##
   # The dependencies of the gem for this specification
diff --git a/lib/rubygems/dependency_resolver/vendor_set.rb b/lib/rubygems/resolver/vendor_set.rb
index 87eb6fd818..e9cbcd8303 100644
--- a/lib/rubygems/dependency_resolver/vendor_set.rb
+++ b/lib/rubygems/resolver/vendor_set.rb
@@ -6,14 +6,14 @@
 #
 # Example:
 #
-#   set = Gem::DependencyResolver::VendorSet.new
+#   set = Gem::Resolver::VendorSet.new
 #
 #   set.add_vendor_gem 'rake', 'vendor/rake'
 #
 # The directory vendor/rake must contain an unpacked rake gem along with a
 # rake.gemspec (watching the given name).
 
-class Gem::DependencyResolver::VendorSet < Gem::DependencyResolver::Set
+class Gem::Resolver::VendorSet < Gem::Resolver::Set
 
   def initialize # :nodoc:
     @directories = {}
@@ -47,7 +47,7 @@ class Gem::DependencyResolver::VendorSet < Gem::DependencyResolver::Set
       req.matches_spec? spec
     end.map do |spec|
       source = Gem::Source::Vendor.new @directories[spec]
-      Gem::DependencyResolver::VendorSpecification.new self, spec, source
+      Gem::Resolver::VendorSpecification.new self, spec, source
     end
   end
 
diff --git a/lib/rubygems/dependency_resolver/vendor_specification.rb b/lib/rubygems/resolver/vendor_specification.rb
index 27b2fd6df2..24e033d084 100644
--- a/lib/rubygems/dependency_resolver/vendor_specification.rb
+++ b/lib/rubygems/resolver/vendor_specification.rb
@@ -3,7 +3,7 @@
 # and is being loaded through a gem dependencies file through the +path:+
 # option.
 
-class Gem::DependencyResolver::VendorSpecification < Gem::DependencyResolver::SpecSpecification
+class Gem::Resolver::VendorSpecification < Gem::Resolver::SpecSpecification
 
   def == other # :nodoc:
     self.class === other and
diff --git a/lib/rubygems/source.rb b/lib/rubygems/source.rb
index b39b3ae69d..a40a27594b 100644
--- a/lib/rubygems/source.rb
+++ b/lib/rubygems/source.rb
@@ -28,7 +28,9 @@ class Gem::Source
     case other
     when Gem::Source::Installed,
          Gem::Source::Local,
-         Gem::Source::SpecificFile then
+         Gem::Source::SpecificFile,
+         Gem::Source::Git,
+         Gem::Source::Vendor then
       -1
     when Gem::Source then
       if !@uri
@@ -62,9 +64,9 @@ class Gem::Source
       fetcher = Gem::RemoteFetcher.fetcher
       fetcher.fetch_path bundler_api_uri, nil, true
     rescue Gem::RemoteFetcher::FetchError
-      Gem::DependencyResolver::IndexSet.new self
+      Gem::Resolver::IndexSet.new self
     else
-      Gem::DependencyResolver::APISet.new bundler_api_uri
+      Gem::Resolver::APISet.new bundler_api_uri
     end
   end
 
@@ -90,12 +92,15 @@ class Gem::Source
       end
   end
 
-  def fetch_spec(name)
+  ##
+  # Fetches a specification for the given +name_tuple+.
+
+  def fetch_spec name_tuple
     fetcher = Gem::RemoteFetcher.fetcher
 
-    spec_file_name = name.spec_name
+    spec_file_name = name_tuple.spec_name
 
-    uri = @uri + "#{Gem::MARSHAL_SPEC_DIR}#{spec_file_name}"
+    uri = api_uri + "#{Gem::MARSHAL_SPEC_DIR}#{spec_file_name}"
 
     cache_dir = cache_dir uri
 
@@ -139,7 +144,7 @@ class Gem::Source
     file       = FILES[type]
     fetcher    = Gem::RemoteFetcher.fetcher
     file_name  = "#{file}.#{Gem.marshal_version}"
-    spec_path  = @uri + "#{file_name}.gz"
+    spec_path  = api_uri + "#{file_name}.gz"
     cache_dir  = cache_dir spec_path
     local_file = File.join(cache_dir, file_name)
     retried    = false
@@ -163,18 +168,22 @@ class Gem::Source
 
   def download(spec, dir=Dir.pwd)
     fetcher = Gem::RemoteFetcher.fetcher
-    fetcher.download spec, @uri.to_s, dir
+    fetcher.download spec, api_uri.to_s, dir
   end
 
   def pretty_print q # :nodoc:
     q.group 2, '[Remote:', ']' do
       q.breakable
       q.text @uri.to_s
+      if api = api_uri
+        g.text api
+      end
     end
   end
 
 end
 
+require 'rubygems/source/git'
 require 'rubygems/source/installed'
 require 'rubygems/source/specific_file'
 require 'rubygems/source/local'
diff --git a/lib/rubygems/source/git.rb b/lib/rubygems/source/git.rb
new file mode 100644
index 0000000000..8453aa5fd7
--- /dev/null
+++ b/lib/rubygems/source/git.rb
@@ -0,0 +1,189 @@
+require 'digest'
+require 'rubygems/util'
+
+##
+# A git gem for use in a gem dependencies file.
+#
+# Example:
+#
+#   source =
+#     Gem::Source::Git.new 'rake', 'git@example:rake.git', 'rake-10.1.0', false
+#
+#   spec = source.load_spec 'rake'
+#
+#   source.checkout
+
+class Gem::Source::Git < Gem::Source
+
+  ##
+  # The name of the gem created by this git gem.
+
+  attr_reader :name
+
+  ##
+  # The commit reference used for checking out this git gem.
+
+  attr_reader :reference
+
+  ##
+  # The git repository this gem is sourced from.
+
+  attr_reader :repository
+
+  ##
+  # Does this repository need submodules checked out too?
+
+  attr_reader :need_submodules
+
+  ##
+  # Creates a new git gem source for a gem with the given +name+ that will be
+  # loaded from +reference+ in +repository+.  If +submodules+ is true,
+  # submodules will be checked out when the gem is installed.
+
+  def initialize name, repository, reference, submodules = false
+    super(nil)
+
+    @name            = name
+    @repository      = repository
+    @reference       = reference
+    @need_submodules = submodules
+
+    @git = ENV['git'] || 'git'
+  end
+
+  def <=> other
+    case other
+    when Gem::Source::Git then
+      0
+    when Gem::Source::Installed then
+      -1
+    when Gem::Source then
+      1
+    else
+      nil
+    end
+  end
+
+  def == other # :nodoc:
+    super and
+      @name            == other.name and
+      @repository      == other.repository and
+      @reference       == other.reference and
+      @need_submodules == other.need_submodules
+  end
+
+  ##
+  # Checks out the files for the repository into the install_dir.
+
+  def checkout # :nodoc:
+    cache
+
+    unless File.exist? install_dir then
+      system @git, 'clone', '--quiet', '--no-checkout',
+             repo_cache_dir, install_dir
+    end
+
+    Dir.chdir install_dir do
+      system @git, 'fetch', '--quiet', '--force', '--tags', install_dir
+
+      success = system @git, 'reset', '--quiet', '--hard', @reference
+
+      success &&=
+        system @git, 'submodule', 'update',
+               '--quiet', '--init', '--recursive' if @need_submodules
+
+      success
+    end
+  end
+
+  ##
+  # Creates a local cache repository for the git gem.
+
+  def cache # :nodoc:
+    if File.exist? repo_cache_dir then
+      Dir.chdir repo_cache_dir do
+        system @git, 'fetch', '--quiet', '--force', '--tags',
+               @repository, 'refs/heads/*:refs/heads/*'
+      end
+    else
+      system @git, 'clone', '--quiet', '--bare', '--no-hardlinks',
+             @repository, repo_cache_dir
+    end
+  end
+
+  ##
+  # A short reference for use in git gem directories
+
+  def dir_shortref # :nodoc:
+    rev_parse[0..11]
+  end
+
+  ##
+  # The directory where the git gem will be installed.
+
+  def install_dir # :nodoc:
+    File.join Gem.dir, 'bundler', 'gems', "#{@name}-#{dir_shortref}"
+  end
+
+  ##
+  # Loads a Gem::Specification for +name+ from this git repository.
+
+  def load_spec name
+    cache
+
+    gemspec_reference = "#{@reference}:#{name}.gemspec"
+
+    Dir.chdir repo_cache_dir do
+      source = Gem::Util.popen @git, 'show', gemspec_reference
+
+      source.force_encoding Encoding::UTF_8 if Object.const_defined? :Encoding
+      source.untaint
+
+      begin
+        spec = eval source, binding, gemspec_reference
+
+        return spec if Gem::Specification === spec
+
+        warn "git gem specification for #{@repository} #{gemspec_reference} is not a Gem::Specification (#{spec.class} instead)."
+      rescue SignalException, SystemExit
+        raise
+      rescue SyntaxError, Exception
+        warn "invalid git gem specification for #{@repository} #{gemspec_reference}"
+      end
+    end
+  end
+
+  ##
+  # The directory where the git gem's repository will be cached.
+
+  def repo_cache_dir # :nodoc:
+    File.join Gem.dir, 'cache', 'bundler', 'git', "#{@name}-#{uri_hash}"
+  end
+
+  ##
+  # Converts the git reference for the repository into a commit hash.
+
+  def rev_parse # :nodoc:
+    # HACK no safe equivalent of ` exists on 1.8.7
+    Dir.chdir repo_cache_dir do
+      Gem::Util.popen(@git, 'rev-parse', @reference).strip
+    end
+  end
+
+  ##
+  # A hash for the git gem based on the git repository URI.
+
+  def uri_hash # :nodoc:
+    normalized =
+      if @repository =~ %r%^\w+://(\w+@)?% then
+        uri = URI(@repository).normalize.to_s.sub %r%/$%,''
+        uri.sub(/\A(\w+)/) { $1.downcase }
+      else
+        @repository
+      end
+
+    Digest::SHA1.hexdigest normalized
+  end
+
+end
+
diff --git a/lib/rubygems/source/installed.rb b/lib/rubygems/source/installed.rb
index 8e3a3560bf..2661dd6844 100644
--- a/lib/rubygems/source/installed.rb
+++ b/lib/rubygems/source/installed.rb
@@ -1,6 +1,9 @@
+##
+# Represents an installed gem.  This is used for dependency resolution.
+
 class Gem::Source::Installed < Gem::Source
 
-  def initialize
+  def initialize # :nodoc:
     @uri = nil
   end
 
@@ -9,6 +12,8 @@ class Gem::Source::Installed < Gem::Source
 
   def <=> other
     case other
+    when Gem::Source::Vendor then
+      -1
     when Gem::Source::Installed then
       0
     when Gem::Source then
diff --git a/lib/rubygems/source/local.rb b/lib/rubygems/source/local.rb
index 16a028b2f3..3aae20c8ed 100644
--- a/lib/rubygems/source/local.rb
+++ b/lib/rubygems/source/local.rb
@@ -1,5 +1,10 @@
+##
+# The local source finds gems in the current directory for fulfilling
+# dependencies.
+
 class Gem::Source::Local < Gem::Source
-  def initialize
+
+  def initialize # :nodoc:
     @specs   = nil
     @api_uri = nil
     @uri     = nil
@@ -26,7 +31,7 @@ class Gem::Source::Local < Gem::Source
     "#<%s specs: %p>" % [self.class, keys]
   end
 
-  def load_specs(type)
+  def load_specs type # :nodoc:
     names = []
 
     @specs = {}
@@ -68,8 +73,8 @@ class Gem::Source::Local < Gem::Source
     names
   end
 
-  def find_gem(gem_name, version=Gem::Requirement.default,
-               prerelease=false)
+  def find_gem gem_name, version = Gem::Requirement.default, # :nodoc:
+               prerelease = false
     load_specs :complete
 
     found = []
@@ -91,7 +96,7 @@ class Gem::Source::Local < Gem::Source
     found.max_by { |s| s.version }
   end
 
-  def fetch_spec(name)
+  def fetch_spec name # :nodoc:
     load_specs :complete
 
     if data = @specs[name]
@@ -101,7 +106,7 @@ class Gem::Source::Local < Gem::Source
     end
   end
 
-  def download(spec, cache_dir=nil)
+  def download spec, cache_dir = nil # :nodoc:
     load_specs :complete
 
     @specs.each do |name, data|
diff --git a/lib/rubygems/source/specific_file.rb b/lib/rubygems/source/specific_file.rb
index 8d328b38c2..a7b6c53542 100644
--- a/lib/rubygems/source/specific_file.rb
+++ b/lib/rubygems/source/specific_file.rb
@@ -1,4 +1,12 @@
+##
+# A source representing a single .gem file.  This is used for installation of
+# local gems.
+
 class Gem::Source::SpecificFile < Gem::Source
+
+  ##
+  # Creates a new SpecificFile for the gem in +file+
+
   def initialize(file)
     @uri = nil
     @path = ::File.expand_path(file)
@@ -8,19 +16,22 @@ class Gem::Source::SpecificFile < Gem::Source
     @name = @spec.name_tuple
   end
 
+  ##
+  # The Gem::Specification extracted from this .gem.
+
   attr_reader :spec
 
-  def load_specs(*a)
+  def load_specs *a # :nodoc:
     [@name]
   end
 
-  def fetch_spec(name)
+  def fetch_spec name # :nodoc:
     return @spec if name == @name
     raise Gem::Exception, "Unable to find '#{name}'"
     @spec
   end
 
-  def download(spec, dir=nil)
+  def download spec, dir = nil # :nodoc:
     return @path if spec == @spec
     raise Gem::Exception, "Unable to download '#{spec.full_name}'"
   end
diff --git a/lib/rubygems/source/vendor.rb b/lib/rubygems/source/vendor.rb
index f2cf540c8d..244c4201d8 100644
--- a/lib/rubygems/source/vendor.rb
+++ b/lib/rubygems/source/vendor.rb
@@ -3,8 +3,22 @@
 
 class Gem::Source::Vendor < Gem::Source::Installed
 
-  def initialize uri
-    @uri = uri
+  ##
+  # Creates a new Vendor source for a gem that was unpacked at +path+.
+
+  def initialize path
+    @uri = path
+  end
+
+  def <=> other
+    case other
+    when Gem::Source::Vendor then
+      0
+    when Gem::Source then
+      1
+    else
+      nil
+    end
   end
 
 end
diff --git a/lib/rubygems/source_list.rb b/lib/rubygems/source_list.rb
index e6da50c2e5..e01f11cc1e 100644
--- a/lib/rubygems/source_list.rb
+++ b/lib/rubygems/source_list.rb
@@ -1,5 +1,18 @@
 require 'rubygems/source'
 
+##
+# The SourceList represents the sources rubygems has been configured to use.
+# A source may be created from an array of sources:
+#
+#   Gem::SourceList.from %w[https://rubygems.example https://internal.example]
+#
+# Or by adding them:
+#
+#   sources = Gem::SourceList.new
+#   sources.add 'https://rubygems.example'
+#
+# The most common way to get a SourceList is Gem.sources.
+
 class Gem::SourceList
 
   include Enumerable
@@ -91,7 +104,7 @@ class Gem::SourceList
     @sources.empty?
   end
 
-  def ==(other)
+  def == other # :nodoc:
     to_a == other
   end
 
diff --git a/lib/rubygems/spec_fetcher.rb b/lib/rubygems/spec_fetcher.rb
index 22fa68db69..12b8fb27d8 100644
--- a/lib/rubygems/spec_fetcher.rb
+++ b/lib/rubygems/spec_fetcher.rb
@@ -34,6 +34,10 @@ class Gem::SpecFetcher
 
   @fetcher = nil
 
+  ##
+  # Default fetcher instance.  Use this instead of ::new to reduce object
+  # allocation.
+
   def self.fetcher
     @fetcher ||= new
   end
@@ -43,8 +47,8 @@ class Gem::SpecFetcher
   end
 
   ##
-  # Creates a new SpecFetcher.  Ordinarily you want to use
-  # Gem::SpecFetcher::fetcher which uses the Gem.sources.
+  # Creates a new SpecFetcher.  Ordinarily you want to use the default fetcher
+  # from Gem::SpecFetcher::fetcher which uses the Gem.sources.
   #
   # If you need to retrieve specifications from a different +source+, you can
   # send it as an argument.
@@ -84,7 +88,11 @@ class Gem::SpecFetcher
     rejected_specs = {}
 
     if dependency.prerelease?
-      type = :complete
+      if dependency.specific?
+        type = :complete
+      else
+        type = :abs_latest
+      end
     elsif dependency.latest_version?
       type = :latest
     else
@@ -224,6 +232,12 @@ class Gem::SpecFetcher
                     tuples_for(source, :released)
 
                   names.sort
+                when :abs_latest
+                  names =
+                    tuples_for(source, :prerelease, true) +
+                    tuples_for(source, :latest)
+
+                  names.sort
                 when :prerelease
                   tuples_for(source, :prerelease)
                 else
@@ -239,7 +253,11 @@ class Gem::SpecFetcher
     [list, errors]
   end
 
-  def tuples_for(source, type, gracefully_ignore=false)
+  ##
+  # Retrieves NameTuples from +source+ of the given +type+ (:prerelease,
+  # etc.).  If +gracefully_ignore+ is true, errors are ignored.
+
+  def tuples_for(source, type, gracefully_ignore=false) # :nodoc:
     cache = @caches[type]
 
     tuples =
diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index 308aa6f011..b95e2c0699 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -12,6 +12,7 @@ require 'rubygems/platform'
 require 'rubygems/deprecate'
 require 'rubygems/basic_specification'
 require 'rubygems/stub_specification'
+require 'rubygems/util/stringio'
 
 # :stopdoc:
 # date.rb can't be loaded for `make install` due to miniruby
@@ -2165,7 +2166,7 @@ class Gem::Specification < Gem::BasicSpecification
   end
 
   ##
-  # Used by Gem::DependencyResolver to order Gem::Specification objects
+  # Used by Gem::Resolver to order Gem::Specification objects
 
   def source # :nodoc:
     self
@@ -2363,7 +2364,7 @@ class Gem::Specification < Gem::BasicSpecification
       builder << self
       ast = builder.tree
 
-      io = StringIO.new
+      io = Gem::StringSink.new
       io.set_encoding Encoding::UTF_8 if Object.const_defined? :Encoding
 
       Psych::Visitors::Emitter.new(io).accept(ast)
diff --git a/lib/rubygems/test_case.rb b/lib/rubygems/test_case.rb
index b04cbfc1f3..d1b471f619 100644
--- a/lib/rubygems/test_case.rb
+++ b/lib/rubygems/test_case.rb
@@ -233,6 +233,8 @@ class Gem::TestCase < MiniTest::Unit::TestCase
                    ruby
                  end
 
+    @git = ENV['GIT'] || 'git'
+
     Gem.ensure_gem_subdirectories @gemhome
 
     @orig_LOAD_PATH = $LOAD_PATH.dup
@@ -373,6 +375,64 @@ class Gem::TestCase < MiniTest::Unit::TestCase
   end
 
   ##
+  # A git_gem is used with a gem dependencies file.  The gem created here
+  # has no files, just a gem specification for the given +name+ and +version+.
+  #
+  # Yields the +specification+ to the block, if given
+
+  def git_gem name = 'a', version = 1
+    have_git?
+
+    directory = File.join 'git', name
+    directory = File.expand_path directory
+
+    git_spec = Gem::Specification.new name, version do |specification|
+      yield specification if block_given?
+    end
+
+    FileUtils.mkdir_p directory
+
+    gemspec = "#{name}.gemspec"
+
+    open File.join(directory, gemspec), 'w' do |io|
+      io.write git_spec.to_ruby
+    end
+
+    head = nil
+
+    Dir.chdir directory do
+      unless File.exist? '.git' then
+        system @git, 'init', '--quiet'
+        system @git, 'config', 'user.name',  'RubyGems Tests'
+        system @git, 'config', 'user.email', 'rubygems@example'
+      end
+
+      system @git, 'add', gemspec
+      system @git, 'commit', '-a', '-m', 'a non-empty commit message', '--quiet'
+      head = Gem::Util.popen('git', 'rev-parse', 'master').strip
+    end
+
+    return name, git_spec.version, directory, head
+  end
+
+  ##
+  # Skips this test unless you have a git executable
+
+  def have_git?
+    return if in_path? @git
+
+    skip 'cannot find git executable, use GIT environment variable to set'
+  end
+
+  def in_path? executable # :nodoc:
+    return true if %r%\A([A-Z]:|/)% =~ executable and File.exist? executable
+
+    ENV['PATH'].split(File::PATH_SEPARATOR).any? do |directory|
+      File.exist? File.join directory, executable
+    end
+  end
+
+  ##
   # Builds and installs the Gem::Specification +spec+
 
   def install_gem spec, options = {}
@@ -1082,21 +1142,21 @@ Also, a list:
   end
 
   ##
-  # Constructs a Gem::DependencyResolver::DependencyRequest from a
+  # Constructs a Gem::Resolver::DependencyRequest from a
   # Gem::Dependency +dep+, a +from_name+ and +from_version+ requesting the
   # dependency and a +parent+ DependencyRequest
 
   def dependency_request dep, from_name, from_version, parent = nil
     remote = Gem::Source.new @uri
 
-    parent ||= Gem::DependencyResolver::DependencyRequest.new \
+    parent ||= Gem::Resolver::DependencyRequest.new \
       dep, nil
 
-    spec = Gem::DependencyResolver::IndexSpecification.new \
+    spec = Gem::Resolver::IndexSpecification.new \
       nil, from_name, from_version, remote, Gem::Platform::RUBY
-    activation = Gem::DependencyResolver::ActivationRequest.new spec, parent
+    activation = Gem::Resolver::ActivationRequest.new spec, parent
 
-    Gem::DependencyResolver::DependencyRequest.new dep, activation
+    Gem::Resolver::DependencyRequest.new dep, activation
   end
 
   ##
diff --git a/lib/rubygems/util.rb b/lib/rubygems/util.rb
new file mode 100644
index 0000000000..e862458d21
--- /dev/null
+++ b/lib/rubygems/util.rb
@@ -0,0 +1,65 @@
+module Gem::Util
+  ##
+  # Zlib::GzipReader wrapper that unzips +data+.
+
+  def self.gunzip(data)
+    require 'zlib'
+    require 'rubygems/util/stringio'
+    data = Gem::StringSource.new data
+
+    unzipped = Zlib::GzipReader.new(data).read
+    unzipped.force_encoding Encoding::BINARY if Object.const_defined? :Encoding
+    unzipped
+  end
+
+  ##
+  # Zlib::GzipWriter wrapper that zips +data+.
+
+  def self.gzip(data)
+    require 'zlib'
+    require 'rubygems/util/stringio'
+    zipped = Gem::StringSink.new
+    zipped.set_encoding Encoding::BINARY if Object.const_defined? :Encoding
+
+    Zlib::GzipWriter.wrap zipped do |io| io.write data end
+
+    zipped.string
+  end
+
+  ##
+  # A Zlib::Inflate#inflate wrapper
+
+  def self.inflate(data)
+    require 'zlib'
+    Zlib::Inflate.inflate data
+  end
+
+  ##
+  # This calls IO.popen where it accepts an array for a +command+ (Ruby 1.9+)
+  # and implements an IO.popen-like behavior where it does not accept an array
+  # for a command.
+
+  def self.popen *command
+    begin
+      r, = IO.popen command
+    rescue TypeError # ruby 1.8 only supports string command
+      r, w = IO.pipe
+
+      pid = fork do
+        STDIN.close
+        STDOUT.reopen w
+
+        exec(*command)
+      end
+
+      w.close
+
+      Process.wait pid
+
+      r
+    end
+
+    r.read
+  end
+
+end
diff --git a/lib/rubygems/util/stringio.rb b/lib/rubygems/util/stringio.rb
new file mode 100644
index 0000000000..2ea69617bc
--- /dev/null
+++ b/lib/rubygems/util/stringio.rb
@@ -0,0 +1,34 @@
+class Gem::StringSink
+  def initialize
+    @string = ""
+  end
+
+  attr_reader :string
+
+  def write(s)
+    @string += s
+    s.size
+  end
+
+  def set_encoding(enc)
+    @string.force_encoding enc
+  end
+end
+
+class Gem::StringSource
+  def initialize(str)
+    @string = str.dup
+  end
+
+  def read(count=nil)
+    if count
+      @string.slice!(0,count)
+    else
+      s = @string
+      @string = ""
+      s
+    end
+  end
+
+  alias_method :readpartial, :read
+end