Add knife-rehash command for subcommand location hashing

`knife rehash` stores the paths to knife plugins in a specially
formatted plugin_manifest entry.  This lowers the overhead of
subsequent knife invocations.

6 files changed, 478 insertions, 145 deletions

diff --git a/lib/chef/knife/core/custom_manifest_loader.rb b/lib/chef/knife/core/custom_manifest_loader.rb
new file mode 100644
index 0000000000..ae8a8199b8
--- /dev/null
+++ b/lib/chef/knife/core/custom_manifest_loader.rb
@@ -0,0 +1,70 @@
+# Author:: Steven Danna (<steve@chef.io>)
+# Copyright:: Copyright (c) 2015 Chef Software, Inc
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'chef/version'
+class Chef
+  class Knife
+    class SubcommandLoader
+
+      #
+      # Load a subcommand from a user-supplied
+      # manifest file
+      #
+      class CustomManifestLoader < Chef::Knife::SubcommandLoader
+        attr_accessor :manifest
+        def initialize(chef_config_dir, plugin_manifest)
+          super(chef_config_dir)
+          @manifest = plugin_manifest
+        end
+
+        # If the user has created a ~/.chef/plugin_manifest.json file, we'll use
+        # that instead of inspecting the on-system gems to find the plugins. The
+        # file format is expected to look like:
+        #
+        #   { "plugins": {
+        #       "knife-ec2": {
+        #         "paths": [
+        #           "/home/alice/.rubymanagerthing/gems/knife-ec2-x.y.z/lib/chef/knife/ec2_server_create.rb",
+        #           "/home/alice/.rubymanagerthing/gems/knife-ec2-x.y.z/lib/chef/knife/ec2_server_delete.rb"
+        #         ]
+        #       }
+        #     }
+        #   }
+        #
+        # Extraneous content in this file is ignored. This intentional so that we
+        # can adapt the file format for potential behavior changes to knife in
+        # the future.
+        def find_subcommands_via_manifest
+          # Format of subcommand_files is "relative_path" (something you can
+          # Kernel.require()) => full_path. The relative path isn't used
+          # currently, so we just map full_path => full_path.
+          subcommand_files = {}
+          manifest["plugins"].each do |plugin_name, plugin_manifest|
+            plugin_manifest["paths"].each do |cmd_path|
+              subcommand_files[cmd_path] = cmd_path
+            end
+          end
+          subcommand_files.merge(find_subcommands_via_dirglob)
+        end
+
+        def subcommand_files
+          subcommand_files ||= (find_subcommands_via_manifest.values + site_subcommands).flatten.uniq
+        end
+      end
+    end
+  end
+end
diff --git a/lib/chef/knife/core/gem_glob_loader.rb b/lib/chef/knife/core/gem_glob_loader.rb
new file mode 100644
index 0000000000..fc21687c80
--- /dev/null
+++ b/lib/chef/knife/core/gem_glob_loader.rb
@@ -0,0 +1,138 @@
+# Author:: Christopher Brown (<cb@opscode.com>)
+# Author:: Daniel DeLeo (<dan@opscode.com>)
+# Copyright:: Copyright (c) 2009, 2011 Opscode, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'chef/version'
+require 'chef/util/path_helper'
+class Chef
+  class Knife
+    class SubcommandLoader
+      class GemGlobLoader < Chef::Knife::SubcommandLoader
+        MATCHES_CHEF_GEM = %r{/chef-[\d]+\.[\d]+\.[\d]+}.freeze
+        MATCHES_THIS_CHEF_GEM = %r{/chef-#{Chef::VERSION}(-\w+)?(-\w+)?/}.freeze
+
+        def subcommand_files
+          @subcommand_files ||= (gem_and_builtin_subcommands.values + site_subcommands).flatten.uniq
+        end
+
+        # Returns a Hash of paths to knife commands built-in to chef, or installed via gem.
+        # If rubygems is not installed, falls back to globbing the knife directory.
+        # The Hash is of the form {"relative/path" => "/absolute/path"}
+        #--
+        # Note: the "right" way to load the plugins is to require the relative path, i.e.,
+        #   require 'chef/knife/command'
+        # but we're getting frustrated by bugs at every turn, and it's slow besides. So
+        # subcommand loader has been modified to load the plugins by using Kernel.load
+        # with the absolute path.
+        def gem_and_builtin_subcommands
+          require 'rubygems'
+          find_subcommands_via_rubygems
+        rescue LoadError
+          find_subcommands_via_dirglob
+        end
+
+        def find_subcommands_via_dirglob
+          # The "require paths" of the core knife subcommands bundled with chef
+          files = Dir[File.join(Chef::Util::PathHelper.escape_glob(File.expand_path('../../../knife', __FILE__)), '*.rb')]
+          subcommand_files = {}
+          files.each do |knife_file|
+            rel_path = knife_file[/#{CHEF_ROOT}#{Regexp.escape(File::SEPARATOR)}(.*)\.rb/,1]
+            subcommand_files[rel_path] = knife_file
+          end
+          subcommand_files
+        end
+
+        def find_subcommands_via_rubygems
+          files = find_files_latest_gems 'chef/knife/*.rb'
+          subcommand_files = {}
+          files.each do |file|
+            rel_path = file[/(#{Regexp.escape File.join('chef', 'knife', '')}.*)\.rb/, 1]
+
+            # When not installed as a gem (ChefDK/appbundler in particular), AND
+            # a different version of Chef is installed via gems, `files` will
+            # include some files from the 'other' Chef install. If this contains
+            # a knife command that doesn't exist in this version of Chef, we will
+            # get a LoadError later when we try to require it.
+            next if from_different_chef_version?(file)
+
+            subcommand_files[rel_path] = file
+          end
+
+          subcommand_files.merge(find_subcommands_via_dirglob)
+        end
+
+        private
+
+        def find_files_latest_gems(glob, check_load_path=true)
+          files = []
+
+          if check_load_path
+            files = $LOAD_PATH.map { |load_path|
+              Dir["#{File.expand_path glob, Chef::Util::PathHelper.escape_glob(load_path)}#{Gem.suffix_pattern}"]
+            }.flatten.select { |file| File.file? file.untaint }
+          end
+
+          gem_files = latest_gem_specs.map do |spec|
+            # Gem::Specification#matches_for_glob wasn't added until RubyGems 1.8
+            if spec.respond_to? :matches_for_glob
+              spec.matches_for_glob("#{glob}#{Gem.suffix_pattern}")
+            else
+              check_spec_for_glob(spec, glob)
+            end
+          end.flatten
+
+          files.concat gem_files
+          files.uniq! if check_load_path
+
+          return files
+        end
+
+        def latest_gem_specs
+          @latest_gem_specs ||= if Gem::Specification.respond_to? :latest_specs
+                                  Gem::Specification.latest_specs(true)  # find prerelease gems
+                                else
+                                  Gem.source_index.latest_specs(true)
+                                end
+        end
+
+        def check_spec_for_glob(spec, glob)
+          dirs = if spec.require_paths.size > 1 then
+                   "{#{spec.require_paths.join(',')}}"
+                 else
+                   spec.require_paths.first
+                 end
+
+          glob = File.join(Chef::Util::PathHelper.escape_glob(spec.full_gem_path, dirs), glob)
+
+          Dir[glob].map { |f| f.untaint }
+        end
+
+        def from_different_chef_version?(path)
+          matches_any_chef_gem?(path) && !matches_this_chef_gem?(path)
+        end
+
+        def matches_any_chef_gem?(path)
+          path =~ MATCHES_CHEF_GEM
+        end
+
+        def matches_this_chef_gem?(path)
+          path =~ MATCHES_THIS_CHEF_GEM
+        end
+      end
+    end
+  end
+end
diff --git a/lib/chef/knife/core/hashed_command_loader.rb b/lib/chef/knife/core/hashed_command_loader.rb
new file mode 100644
index 0000000000..6729e59bb0
--- /dev/null
+++ b/lib/chef/knife/core/hashed_command_loader.rb
@@ -0,0 +1,75 @@
+# Author:: Steven Danna (<steve@chef.io>)
+# Copyright:: Copyright (c) 2015 Chef Software, Inc
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'chef/version'
+class Chef
+  class Knife
+    class SubcommandLoader
+      #
+      # Load a subcommand from a pre-computed path
+      # for the given command.
+      #
+      class HashedCommandLoader < Chef::Knife::SubcommandLoader
+        KEY = '_autogenerated_command_paths'
+
+        attr_accessor :manifest
+        def initialize(chef_config_dir, plugin_manifest)
+          super(chef_config_dir)
+          @manifest = plugin_manifest
+        end
+
+        def guess_category(args)
+          category_words = positional_arguments(args)
+          category_words.map! { |w| w.split('-') }.flatten!
+          find_longest_key(manifest[KEY]["plugins_by_category"], category_words, ' ')
+        end
+
+        def list_commands(pref_category=nil)
+          if pref_category || manifest[KEY]["plugins_by_category"].key?(pref_category)
+            { pref_category => manifest[KEY]["plugins_by_category"][pref_category] }
+          else
+            manifest[KEY]["plugins_by_category"]
+          end
+        end
+
+        def subcommand_files
+          manifest[KEY]["plugins_paths"].values.flatten
+        end
+
+        def load_command(args)
+          paths = manifest[KEY]["plugins_paths"][subcommand_for_args(args)]
+          if paths.nil? || paths.empty? || (! paths.is_a? Array)
+            false
+          else
+            paths.each do |sc|
+              Kernel.load sc
+            end
+            true
+          end
+        end
+
+        def subcommand_for_args(args)
+          if manifest[KEY]["plugins_paths"].key?(args)
+            args
+          else
+            find_longest_key(manifest[KEY]["plugins_paths"], args, "_")
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/chef/knife/core/subcommand_loader.rb b/lib/chef/knife/core/subcommand_loader.rb
index a8705c724f..8aa2205679 100644
--- a/lib/chef/knife/core/subcommand_loader.rb
+++ b/lib/chef/knife/core/subcommand_loader.rb
@@ -18,19 +18,66 @@
 
 require 'chef/version'
 require 'chef/util/path_helper'
+require 'chef/knife/core/gem_glob_loader'
+require 'chef/knife/core/hashed_command_loader'
+require 'chef/knife/core/custom_manifest_loader'
+
 class Chef
   class Knife
+    #
+    # Public Methods of a Subcommand Loader
+    #
+    # load_commands            - loads all available subcommands
+    # load_command(args)       - loads subcommands for the given args
+    # list_commands(args)      - lists all available subcommands,
+    #                            optionally filtering by category
+    # subcommand_files         - returns an array of all subcommand files
+    #                            that could be loaded
+    # commnad_class_from(args) - returns the subcommand class for the
+    #                            user-requested command
+    #
     class SubcommandLoader
-
-      MATCHES_CHEF_GEM = %r{/chef-[\d]+\.[\d]+\.[\d]+}.freeze
-      MATCHES_THIS_CHEF_GEM = %r{/chef-#{Chef::VERSION}(-\w+)?(-\w+)?/}.freeze
-
       attr_reader :chef_config_dir
       attr_reader :env
 
-      def initialize(chef_config_dir, env=nil)
+      # A small factory method.  Eventually, this is the only place
+      # where SubcommandLoader should know about its subclasses, but
+      # to maintain backwards compatibility many of the instance
+      # methods in this base class contain default implementations
+      # of the functions sub classes should otherwise provide
+      # or directly instantiate the appropriate subclass
+      def self.for_config(chef_config_dir)
+        if autogenerated_manifest?
+          Knife::SubcommandLoader::HashedCommandLoader.new(chef_config_dir, plugin_manifest)
+        elsif custom_manifest?
+          Knife::SubcommandLoader::CustomManifestLoader.new(chef_config_dir, plugin_manifest)
+        else
+          Knife::SubcommandLoader::GemGlobLoader.new(chef_config_dir)
+        end
+      end
+
+      def self.plugin_manifest?
+        plugin_manifest_path && File.exist?(plugin_manifest_path)
+      end
+
+      def self.autogenerated_manifest?
+        plugin_manifest? && plugin_manifest.key?(HashedCommandLoader::KEY)
+      end
+
+      def self.custom_manifest?
+        plugin_manifest? && plugin_manifest.key?("plugins")
+      end
+
+      def self.plugin_manifest
+        Chef::JSONCompat.from_json(File.read(plugin_manifest_path))
+      end
+
+      def self.plugin_manifest_path
+        Chef::Util::PathHelper.home('.chef', 'plugin_manifest.json')
+      end
+
+      def initialize(chef_config_dir, env = nil)
         @chef_config_dir = chef_config_dir
-        @forced_activate = {}
 
         # Deprecated and un-used instance variable.
         @env = env
@@ -41,82 +88,48 @@ class Chef
 
       # Load all the sub-commands
       def load_commands
+        return true if @loaded
         subcommand_files.each { |subcommand| Kernel.load subcommand }
-        true
+        @loaded = true
       end
 
-      # Returns an Array of paths to knife commands located in chef_config_dir/plugins/knife/
-      # and ~/.chef/plugins/knife/
-      def site_subcommands
-        user_specific_files = []
-
-        if chef_config_dir
-          user_specific_files.concat Dir.glob(File.expand_path("plugins/knife/*.rb", Chef::Util::PathHelper.escape_glob(chef_config_dir)))
-        end
-
-        # finally search ~/.chef/plugins/knife/*.rb
-        Chef::Util::PathHelper.home('.chef', 'plugins', 'knife') do |p|
-          user_specific_files.concat Dir.glob(File.join(Chef::Util::PathHelper.escape_glob(p), '*.rb'))
-        end
+      def force_load
+        @loaded=false
+        load_commands
+      end
 
-        user_specific_files
+      def load_command(_command_args)
+        load_commands
       end
 
-      # Returns a Hash of paths to knife commands built-in to chef, or installed via gem.
-      # If rubygems is not installed, falls back to globbing the knife directory.
-      # The Hash is of the form {"relative/path" => "/absolute/path"}
-      #--
-      # Note: the "right" way to load the plugins is to require the relative path, i.e.,
-      #   require 'chef/knife/command'
-      # but we're getting frustrated by bugs at every turn, and it's slow besides. So
-      # subcommand loader has been modified to load the plugins by using Kernel.load
-      # with the absolute path.
-      def gem_and_builtin_subcommands
-        if have_plugin_manifest?
-          find_subcommands_via_manifest
+      def list_commands(pref_cat = nil)
+        load_commands
+        if pref_cat && Chef::Knife.subcommands_by_category.key?(pref_cat)
+          { pref_cat => Chef::Knife.subcommands_by_category[pref_cat] }
         else
-          # search all gems for chef/knife/*.rb
-          require 'rubygems'
-          find_subcommands_via_rubygems
+          Chef::Knife.subcommands_by_category
         end
-      rescue LoadError
-        find_subcommands_via_dirglob
       end
 
-      def subcommand_files
-        @subcommand_files ||= (gem_and_builtin_subcommands.values + site_subcommands).flatten.uniq
+      def command_class_from(args)
+        cmd_words = positional_arguments(args)
+        load_command(cmd_words)
+        result = Chef::Knife.subcommands[find_longest_key(Chef::Knife.subcommands,
+                                                          cmd_words, '_')]
+        result || Chef::Knife.subcommands[args.first.gsub('-', '_')]
       end
 
-      # If the user has created a ~/.chef/plugin_manifest.json file, we'll use
-      # that instead of inspecting the on-system gems to find the plugins. The
-      # file format is expected to look like:
-      #
-      #   { "plugins": {
-      #       "knife-ec2": {
-      #         "paths": [
-      #           "/home/alice/.rubymanagerthing/gems/knife-ec2-x.y.z/lib/chef/knife/ec2_server_create.rb",
-      #           "/home/alice/.rubymanagerthing/gems/knife-ec2-x.y.z/lib/chef/knife/ec2_server_delete.rb"
-      #         ]
-      #       }
-      #     }
-      #   }
-      #
-      # Extraneous content in this file is ignored. This intentional so that we
-      # can adapt the file format for potential behavior changes to knife in
-      # the future.
-      def find_subcommands_via_manifest
-        # Format of subcommand_files is "relative_path" (something you can
-        # Kernel.require()) => full_path. The relative path isn't used
-        # currently, so we just map full_path => full_path.
-        subcommand_files = {}
-        plugin_manifest["plugins"].each do |plugin_name, plugin_manifest|
-          plugin_manifest["paths"].each do |cmd_path|
-            subcommand_files[cmd_path] = cmd_path
-          end
-        end
-        subcommand_files.merge(find_subcommands_via_dirglob)
+      def guess_category(args)
+        category_words = positional_arguments(args)
+        category_words.map! { |w| w.split('-') }.flatten!
+        find_longest_key(Chef::Knife.subcommands_by_category,
+                         category_words, ' ')
       end
 
+
+      #
+      # This is shared between the custom_manifest_loader and the gem_glob_loader
+      #
       def find_subcommands_via_dirglob
         # The "require paths" of the core knife subcommands bundled with chef
         files = Dir[File.join(Chef::Util::PathHelper.escape_glob(File.expand_path('../../../knife', __FILE__)), '*.rb')]
@@ -128,95 +141,65 @@ class Chef
         subcommand_files
       end
 
-      def find_subcommands_via_rubygems
-        files = find_files_latest_gems 'chef/knife/*.rb'
-        subcommand_files = {}
-        files.each do |file|
-          rel_path = file[/(#{Regexp.escape File.join('chef', 'knife', '')}.*)\.rb/, 1]
-
-          # When not installed as a gem (ChefDK/appbundler in particular), AND
-          # a different version of Chef is installed via gems, `files` will
-          # include some files from the 'other' Chef install. If this contains
-          # a knife command that doesn't exist in this version of Chef, we will
-          # get a LoadError later when we try to require it.
-          next if from_different_chef_version?(file)
-
-          subcommand_files[rel_path] = file
-        end
-
-        subcommand_files.merge(find_subcommands_via_dirglob)
-      end
-
-      def have_plugin_manifest?
-        plugin_manifest_path && File.exist?(plugin_manifest_path)
-      end
-
-      def plugin_manifest
-        Chef::JSONCompat.from_json(File.read(plugin_manifest_path))
-      end
-
-      def plugin_manifest_path
-        Chef::Util::PathHelper.home('.chef', 'plugin_manifest.json')
+      #
+      # Subclassses should define this themselves.  Eventually, this will raise a
+      # NotImplemented error, but for now, we mimic the behavior the user was likely
+      # to get in the past.
+      #
+      def subcommand_files
+        Chef::Log.warn "DEPRECATED: Using Chef::Knife::SubcommandLoader directly is deprecated.
+Please use Chef::Knife::SubcommandLoader.for_config(chef_config_dir, env)"
+        @subcommand_files ||= if Chef::Knife::SubcommandLoader.plugin_manifest?
+                                Chef::Knife::SubcommandLoader::CustomManifestLoader.new(chef_config_dir, env).subcommand_files
+                              else
+                                Chef::Knife::SubcommandLoader::GemGlobLoader.new(chef_config_dir, env).subcommand_files
+                              end
       end
 
-      private
-
-      def find_files_latest_gems(glob, check_load_path=true)
-        files = []
-
-        if check_load_path
-          files = $LOAD_PATH.map { |load_path|
-            Dir["#{File.expand_path glob, Chef::Util::PathHelper.escape_glob(load_path)}#{Gem.suffix_pattern}"]
-          }.flatten.select { |file| File.file? file.untaint }
-        end
-
-        gem_files = latest_gem_specs.map do |spec|
-          # Gem::Specification#matches_for_glob wasn't added until RubyGems 1.8
-          if spec.respond_to? :matches_for_glob
-            spec.matches_for_glob("#{glob}#{Gem.suffix_pattern}")
+      #
+      # Utility function for finding an element in a hash given an array
+      # of words and a separator.  We find the the longest key in the
+      # hash composed of the given words joined by the separator.
+      #
+      def find_longest_key(hash, words, sep = '_')
+        match = nil
+        until match || words.empty?
+          candidate = words.join(sep)
+          if hash.key?(candidate)
+            match = candidate
           else
-            check_spec_for_glob(spec, glob)
+            words.pop
           end
-        end.flatten
-
-        files.concat gem_files
-        files.uniq! if check_load_path
-
-        return files
-      end
-
-      def latest_gem_specs
-        @latest_gem_specs ||= if Gem::Specification.respond_to? :latest_specs
-          Gem::Specification.latest_specs(true)  # find prerelease gems
-        else
-          Gem.source_index.latest_specs(true)
         end
+        match
       end
 
-      def check_spec_for_glob(spec, glob)
-        dirs = if spec.require_paths.size > 1 then
-          "{#{spec.require_paths.join(',')}}"
-        else
-          spec.require_paths.first
-        end
-
-        glob = File.join(Chef::Util::PathHelper.escape_glob(spec.full_gem_path, dirs), glob)
-
-        Dir[glob].map { |f| f.untaint }
+      #
+      # The positional arguments from the argument list provided by the
+      # users. Used to search for subcommands and categories.
+      #
+      # @return [Array<String>]
+      #
+      def positional_arguments(args)
+        args.select { |arg| arg =~ /^(([[:alnum:]])[[:alnum:]\_\-]+)$/ }
       end
 
-      def from_different_chef_version?(path)
-        matches_any_chef_gem?(path) && !matches_this_chef_gem?(path)
-      end
+      # Returns an Array of paths to knife commands located in
+      # chef_config_dir/plugins/knife/ and ~/.chef/plugins/knife/
+      def site_subcommands
+        user_specific_files = []
 
-      def matches_any_chef_gem?(path)
-        path =~ MATCHES_CHEF_GEM
-      end
+        if chef_config_dir
+          user_specific_files.concat Dir.glob(File.expand_path("plugins/knife/*.rb", Chef::Util::PathHelper.escape_glob(chef_config_dir)))
+        end
 
-      def matches_this_chef_gem?(path)
-        path =~ MATCHES_THIS_CHEF_GEM
-      end
+        # finally search ~/.chef/plugins/knife/*.rb
+        Chef::Util::PathHelper.home('.chef', 'plugins', 'knife') do |p|
+          user_specific_files.concat Dir.glob(File.join(Chef::Util::PathHelper.escape_glob(p), '*.rb'))
+        end
 
+        user_specific_files
+      end
     end
   end
 end
diff --git a/lib/chef/knife/null.rb b/lib/chef/knife/null.rb
new file mode 100644
index 0000000000..c8f04e5cd3
--- /dev/null
+++ b/lib/chef/knife/null.rb
@@ -0,0 +1,8 @@
+class Chef
+  class Knife
+    class Null < Chef::Knife
+      def run
+      end
+    end
+  end
+end
diff --git a/lib/chef/knife/rehash.rb b/lib/chef/knife/rehash.rb
new file mode 100644
index 0000000000..ef58a687b8
--- /dev/null
+++ b/lib/chef/knife/rehash.rb
@@ -0,0 +1,59 @@
+#
+# Author:: Steven Danna <steve@chef.io>
+# Copyright:: Copyright (c) 2015 Chef Software, Inc
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require 'chef/knife'
+require 'chef/knife/core/subcommand_loader'
+
+class Chef
+  class Knife
+    class Rehash <  Chef::Knife
+
+      def run
+        if ! Chef::Knife::SubcommandLoader.autogenerated_manifest?
+          ui.msg "Using knife-rehash will speed up knife's load time by caching the location of subcommands on disk"
+          ui.msg "However, you will need to update the cache by running `knife rehash` anytime you install a new knife plugin."
+          ui.confirm "Would you like to continue?"
+        else
+          reload_plugins
+        end
+        write_hash(generate_hash)
+      end
+
+      def reload_plugins
+        Chef::Knife::SubcommandLoader::GemGlobLoader.new(@@chef_config_dir).load_commands
+      end
+
+      def generate_hash
+        output = if Chef::Knife::SubcommandLoader.plugin_manifest?
+                   Chef::Knife::SubcommandLoader.plugin_manifest
+                 else
+                   { Chef::Knife::SubcommandLoader::HashedCommandLoader::KEY => {}}
+                 end
+        output[Chef::Knife::SubcommandLoader::HashedCommandLoader::KEY]['plugins_paths'] = Chef::Knife.subcommand_files
+        output[Chef::Knife::SubcommandLoader::HashedCommandLoader::KEY]['plugins_by_category'] = Chef::Knife.subcommands_by_category
+        output
+      end
+
+      def write_hash(data)
+        File.open(Chef::Knife::SubcommandLoader.plugin_manifest_path, 'w') do |f|
+          f.write(Chef::JSONCompat.to_json_pretty(data))
+        end
+      end
+    end
+  end
+end