Add completion for gem-open and gem-cd

lib/pry/commands/gem_cd.rb

@@ -14,5 +14,9 @@ class Pry
       Dir.chdir(gem_spec(gem).full_gem_path)
       output.puts(Dir.pwd)
     end
+
+    def complete(str)
+      gem_complete(str)
+    end
   end
 end

lib/pry/commands/gem_list.rb

@@ -12,11 +12,7 @@ class Pry
 
     def process(pattern=nil)
       pattern = Regexp.compile(pattern || '')
-      gems    = if Gem::Specification.respond_to?(:each)
-                  Gem::Specification.select{|spec| spec.name =~ pattern }.group_by(&:name)
-                else
-                  Gem.source_index.gems.values.group_by(&:name).select { |gemname, specs| gemname =~ pattern }
-                end
+      gems    = gem_list(pattern).group_by(&:name)
 
       gems.each do |gem, specs|
         specs.sort! do |a,b|

lib/pry/commands/gem_open.rb

@@ -16,5 +16,9 @@ class Pry
         invoke_editor(".", 0, false)
       end
     end
+
+    def complete(str)
+      gem_complete(str)
+    end
   end
 end

lib/pry/helpers/command_helpers.rb

@@ -276,6 +276,28 @@ class Pry
 
         spec or raise CommandError, "Gem `#{gem}` not found"
       end
+
+      # List gems matching a pattern
+      # @param [Regexp] pattern
+      # @return [Array<Gem::Specification>]
+      def gem_list(pattern=/.*/)
+        if Gem::Specification.respond_to?(:each)
+          Gem::Specification.select{|spec| spec.name =~ pattern }
+        else
+          Gem.source_index.gems.values.select{|spec| spec.name =~ pattern }
+        end
+      end
+
+      # Completion function for gem-cd and gem-open
+      # @param [String] so_far what the user's typed so far
+      # @return [Array<String>] completions
+      def gem_complete(so_far)
+        if so_far =~ / ([^ ]*)\z/
+          gem_list(%r{\A#{$2}}).map(&:name)
+        else
+          gem_list.map(&:name)
+        end
+      end
     end
   end
 end