Implement cd - command

The `cd -` command allows a user to toggle between last two scopes.

Example:

  [1] pry(main)> cd :foo
  [2] pry(:foo):1> cd :bar
  [3] pry(:bar):2> cd -
           ^ save :bar and toggle
  [4] pry(:foo):1> cd 44
           ^ we are back at foo
  [5] pry(44):2> cd ..
  [6] pry(:foo):1> cd ..
  [7] pry(main)> cd -
           ^ save main and toggle
  [8] pry(:foo):1>
           ^ we are back at foo

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>
Signed-off-by: Yorick Peterse <yorickpeterse@gmail.com>

lib/pry.rb

@@ -110,8 +110,9 @@ class Pry
       _pry_.binding_stack.clear
       throw(:breakout)
     else
-      # otherwise just pops a binding
-      _pry_.binding_stack.pop
+      # otherwise just pops a binding and stores it as old binding
+      _pry_.command_state["cd"].old_binding = _pry_.binding_stack.pop
+      _pry_.command_state["cd"].append = true
     end
   end
 

lib/pry/default_commands/cd.rb

@@ -9,41 +9,64 @@ class Pry
           Usage: cd [OPTIONS] [--help]
 
           Move into new context (object or scope). As in unix shells use
-          `cd ..` to go back and `cd /` to return to Pry top-level).
-          Complex syntax (e.g cd ../@x/y) also supported.
+          `cd ..` to go back, `cd /` to return to Pry top-level and `cd -`
+          to toggle between last two scopes).
+          Complex syntax (e.g `cd ../@x/y`) also supported.
 
           e.g: `cd @x`
-          e.g: `cd ..
+          e.g: `cd ..`
           e.g: `cd /`
+          e.g: `cd -`
 
           https://github.com/pry/pry/wiki/State-navigation#wiki-Changing_scope
         BANNER
 
         def process
-          path   = arg_string.split(/\//)
+          # Extract command arguments. Delete blank arguments like " ", but
+          # don't delete empty strings like "".
+          path  = arg_string.split(/\//).delete_if { |a| a =~ /\A\s+\z/ }
           stack = _pry_.binding_stack.dup
 
-          # special case when we only get a single "/", return to root
-          stack  = [stack.first] if path.empty?
+          # Save current state values for the sake of restoring them them later
+          # (for example, when an exception raised).
+          old_binding = state.old_binding
+          append      = state.append
+
+          # Special case when we only get a single "/", return to root.
+          if path.empty?
+            set_old_binding(stack.last, true) if old_binding
+            stack = [stack.first]
+          end
 
           path.each do |context|
             begin
               case context.chomp
               when ""
+                set_old_binding(stack.last, true)
                 stack = [stack.first]
               when "::"
+                set_old_binding(stack.last, false)
                 stack.push(TOPLEVEL_BINDING)
               when "."
                 next
               when ".."
                 unless stack.size == 1
-                  stack.pop
+                  set_old_binding(stack.pop, true)
+                end
+              when "-"
+                if state.old_binding
+                  toggle_old_binding(stack, old_binding, append)
                 end
               else
+                unless path.length > 1
+                  set_old_binding(stack.last, false)
+                end
                 stack.push(Pry.binding_for(stack.last.eval(context)))
               end
 
             rescue RescuableException => e
+              set_old_binding(old_binding, append) # Restore previous values.
+
               output.puts "Bad object path: #{arg_string.chomp}. Failed trying to resolve: #{context}"
               output.puts e.inspect
               return
@@ -52,6 +75,43 @@ class Pry
 
           _pry_.binding_stack = stack
         end
+
+        private
+
+        # Toggle old binding value by either appending it to the current stack
+        # (when `append` is `true`) or setting the new one (when `append` is
+        # `false`).
+        #
+        # @param [Array<Binding>] stack The current stack of bindings.
+        # @param [Binding] old_binding The old binding.
+        # @param [Boolean] append The adjunction flag.
+        #
+        # @return [Binding] The new old binding.
+        def toggle_old_binding(stack, old_binding, append)
+          if append
+            stack.push(old_binding)
+            old_binding = stack[-2]
+          else
+            old_binding = stack.pop
+          end
+          append = !append
+
+          set_old_binding(old_binding, append)
+
+          old_binding
+        end
+
+        # Set new old binding and adjunction flag.
+        #
+        # @param [Binding] binding The old binding.
+        # @param [Boolean] append The adjunction flag.
+        #
+        # @return [void]
+        def set_old_binding(binding, append)
+          state.old_binding = binding
+          state.append = append
+        end
+
       end
     end
   end

test/test_default_commands/test_cd.rb

@@ -5,6 +5,333 @@ describe 'Pry::DefaultCommands::Cd' do
     $obj = nil
   end
 
+  describe 'state' do
+    it 'should not to be set up in fresh instance' do
+      instance = nil
+      redirect_pry_io(InputTester.new("cd", "exit-all")) do
+        instance = Pry.new
+        instance.repl
+      end
+
+      instance.command_state["cd"].old_binding.should == nil
+      instance.command_state["cd"].append.should == nil
+    end
+  end
+
+  describe 'old binding toggling with `cd -`' do
+    describe 'when an error was raised' do
+      it 'should ensure cd @ raises SyntaxError' do
+        mock_pry("cd @").should =~ /SyntaxError/
+      end
+
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd @", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.should == nil
+        instance.command_state["cd"].append.should == nil
+
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd @", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == false
+
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd @", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :mon_dogg
+        instance.command_state["cd"].append.should == true
+      end
+    end
+
+    describe 'when using simple cd syntax' do
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :mon_dogg
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with multple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == false
+      end
+    end
+
+    describe 'series of cd calls' do
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd 42", "cd :john_dogg", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 42
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd 42", "cd :john_dogg", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with multple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd 42", "cd :john_dogg", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 42
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with fuzzy `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :mon_dogg", "cd -", "cd 42", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 42
+        instance.command_state["cd"].append.should == true
+      end
+    end
+
+    describe 'when using cd ..' do
+      before do
+        $obj = Object.new
+        $obj.instance_variable_set(:@x, 66)
+        $obj.instance_variable_set(:@y, 79)
+      end
+
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ..", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == true
+
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd $obj/@x/../@y", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 66
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ..", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == false
+
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd $obj/@x/../@y", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 79
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with multiple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ..", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == true
+
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd $obj/@x/../@y", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == 66
+        instance.command_state["cd"].append.should == true
+      end
+    end
+
+    describe 'when using cd ::' do
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ::", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ::", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with multiple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd ::", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == false
+      end
+    end
+
+    describe 'when using cd /' do
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd /", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd /", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == TOPLEVEL_BINDING.eval("self")
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with multiple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd /", "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :john_dogg
+        instance.command_state["cd"].append.should == true
+      end
+    end
+
+    describe 'when using ^D (Control-D) key press' do
+      before do
+        @control_d = "Pry::DEFAULT_CONTROL_D_HANDLER.call('', _pry_)"
+      end
+
+      it 'should keep correct old binding' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd :mon_dogg",
+                                        "cd :kyr_dogg", @control_d, "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :kyr_dogg
+        instance.command_state["cd"].append.should == true
+      end
+
+      it 'should toggle with a single `cd -` call' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd :mon_dogg",
+                                        "cd :kyr_dogg", @control_d, "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :mon_dogg
+        instance.command_state["cd"].append.should == false
+      end
+
+      it 'should toggle with multiple `cd -` calls' do
+        instance = nil
+        redirect_pry_io(InputTester.new("cd :john_dogg", "cd :mon_dogg",
+                                        "cd :kyr_dogg", @control_d, "cd -", "cd -", "exit-all")) do
+          instance = Pry.new
+          instance.repl
+        end
+
+        instance.command_state["cd"].old_binding.eval("self").should == :kyr_dogg
+        instance.command_state["cd"].append.should == true
+      end
+    end
+
+    it 'should not toggle when there is no old binding' do
+      instance = nil
+      redirect_pry_io(InputTester.new("cd -", "exit-all")) do
+        instance = Pry.new
+        instance.repl
+      end
+
+      instance.command_state["cd"].old_binding.should == nil
+      instance.command_state["cd"].append.should == nil
+
+      redirect_pry_io(InputTester.new("cd -", "cd -", "exit-all")) do
+        instance = Pry.new
+        instance.repl
+      end
+
+      instance.command_state["cd"].old_binding.should == nil
+      instance.command_state["cd"].append.should == nil
+    end
+  end
+
   it 'should cd into simple input' do
     b = Pry.binding_for(Object.new)
     b.eval("x = :mon_ouie")