Add path completion to Readline.

Arguably the most common use for tab completion is paths, so let's support
it! Calls to #ask can now take `:path => true` which will enable tab
completion relative to the current working directory on systems that have
Readline support.

Author: georgebrock

lib/thor/line_editor/readline.rb

@@ -8,6 +8,7 @@ def self.available?
       end
 
       def readline
+        ::Readline.completion_append_character = nil
         ::Readline.completion_proc = completion_proc
         ::Readline.readline(prompt, add_to_history?)
       end
@@ -19,7 +20,9 @@ def add_to_history?
       end
 
       def completion_proc
-        if completion_options.any?
+        if use_path_completion?
+          Proc.new { |text| PathCompletion.new(text).matches }
+        elsif completion_options.any?
           Proc.new do |text|
             completion_options.select { |option| option.start_with?(text) }
           end
@@ -29,6 +32,46 @@ def completion_proc
       def completion_options
         options.fetch(:limited_to, [])
       end
+
+      def use_path_completion?
+        options.fetch(:path, false)
+      end
+
+      class PathCompletion
+        def initialize(text)
+          @text = text
+        end
+
+        def matches
+          relative_matches
+        end
+
+        private
+
+        attr_reader :text
+
+        def relative_matches
+          absolute_matches.map { |path| path.sub(base_path, '') }
+        end
+
+        def absolute_matches
+          Dir[glob_pattern].map do |path|
+            if File.directory?(path)
+              "#{path}/"
+            else
+              path
+            end
+          end
+        end
+
+        def glob_pattern
+          "#{base_path}#{text}*"
+        end
+
+        def base_path
+          "#{Dir.pwd}/"
+        end
+      end
     end
   end
 end

lib/thor/shell/basic.rb

@@ -43,13 +43,20 @@ def padding=(value)
       # If asking for sensitive information, the :echo option can be set
       # to false to mask user input from $stdin.
       #
+      # If the required input is a path, then set the path option to
+      # true. This will enable tab completion for file paths relative
+      # to the current working directory on systems that support
+      # Readline.
+      #
       # ==== Example
       # ask("What is your name?")
       #
       # ask("What is your favorite Neopolitan flavor?", :limited_to => ["strawberry", "chocolate", "vanilla"])
       #
       # ask("What is your password?", :echo => false)
       #
+      # ask("Where should the file be saved?", :path => true)
+      #
       def ask(statement, *args)
         options = args.last.is_a?(Hash) ? args.pop : {}
         color = args.first

spec/line_editor/readline_spec.rb

@@ -4,6 +4,7 @@
   before do
     unless defined? ::Readline
       ::Readline = double('Readline')
+      allow(::Readline).to receive(:completion_append_character=).with(nil)
     end
   end
 
@@ -45,5 +46,15 @@
       editor = Thor::LineEditor::Readline.new('Best food: ', :limited_to => ['Apples', 'Chicken', 'Chocolate'])
       editor.readline
     end
+
+    it 'provides path tab completion when given the path option' do
+      expect(::Readline).to receive(:readline)
+      expect(::Readline).to receive(:completion_proc=) do |proc|
+        expect(proc.call('../line_ed').sort).to eq ['../line_editor/', '../line_editor_spec.rb'].sort
+      end
+
+      editor = Thor::LineEditor::Readline.new('Path to file: ', :path => true)
+      Dir.chdir(File.dirname(__FILE__)) { editor.readline }
+    end
   end
 end