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diff --git a/trunk/lib/rubygems/gem_path_searcher.rb b/trunk/lib/rubygems/gem_path_searcher.rb
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+++ b/trunk/lib/rubygems/gem_path_searcher.rb
@@ -0,0 +1,84 @@
+#--
+# Copyright 2006 by Chad Fowler, Rich Kilmer, Jim Weirich and others.
+# All rights reserved.
+# See LICENSE.txt for permissions.
+#++
+
+require 'rubygems'
+
+#
+# GemPathSearcher has the capability to find loadable files inside
+# gems.  It generates data up front to speed up searches later.
+#
+class Gem::GemPathSearcher
+
+  #
+  # Initialise the data we need to make searches later.
+  #
+  def initialize
+    # We want a record of all the installed gemspecs, in the order
+    # we wish to examine them.
+    @gemspecs = init_gemspecs
+    # Map gem spec to glob of full require_path directories.
+    # Preparing this information may speed up searches later.
+    @lib_dirs = {}
+    @gemspecs.each do |spec|
+      @lib_dirs[spec.object_id] = lib_dirs_for(spec)
+    end
+  end
+
+  # 
+  # Look in all the installed gems until a matching _path_ is found.
+  # Return the _gemspec_ of the gem where it was found.  If no match
+  # is found, return nil.
+  #
+  # The gems are searched in alphabetical order, and in reverse
+  # version order.
+  #
+  # For example:
+  #
+  #   find('log4r')              # -> (log4r-1.1 spec)
+  #   find('log4r.rb')           # -> (log4r-1.1 spec)
+  #   find('rake/rdoctask')      # -> (rake-0.4.12 spec)
+  #   find('foobarbaz')          # -> nil
+  #
+  # Matching paths can have various suffixes ('.rb', '.so', and
+  # others), which may or may not already be attached to _file_.
+  # This method doesn't care about the full filename that matches;
+  # only that there is a match.
+  # 
+  def find(path)
+    @gemspecs.each do |spec|
+      return spec if matching_file(spec, path)
+    end
+    nil
+  end
+
+  private
+
+  # Attempts to find a matching path using the require_paths of the
+  # given _spec_.
+  #
+  # Some of the intermediate results are cached in @lib_dirs for
+  # speed.
+  def matching_file(spec, path)  # :doc:
+    glob = File.join @lib_dirs[spec.object_id], "#{path}#{Gem.suffix_pattern}"
+    return true unless Dir[glob].select { |f| File.file?(f.untaint) }.empty?
+  end
+
+  # Return a list of all installed gemspecs, sorted by alphabetical
+  # order and in reverse version order.
+  def init_gemspecs
+    Gem.source_index.map { |_, spec| spec }.sort { |a,b|
+      (a.name <=> b.name).nonzero? || (b.version <=> a.version)
+    }
+  end
+
+  # Returns library directories glob for a gemspec.  For example,
+  #   '/usr/local/lib/ruby/gems/1.8/gems/foobar-1.0/{lib,ext}'
+  def lib_dirs_for(spec)
+    "#{spec.full_gem_path}/{#{spec.require_paths.join(',')}}"
+  end
+
+end
+