Implement 'cd -'

lib/irb/command/cd.rb

@@ -7,31 +7,39 @@ class CD < Base
       description "Move into the given object or leave the current context."
 
       help_message(<<~HELP)
-        Usage: cd ([target]|..)
+        Usage: cd ([target]|..|-)
 
-        When given an object, cd will move into that object, making it the current context.
-        When given "..", cd will leave the current context, moving back to the previous context.
-        When given no arguments, cd will move back to the top-level (main object) context.
+
+        When given:
+        - an object, cd will move into that object, making it the current context.
+        - "..", cd will leave the current context, moving back to the previous context.
+        - "-", cd will toggle between the last 2 contexts. This does not work with other workspace commands.
+        - no arguments, cd will move back to the top-level (main object) context.
 
         Examples:
 
           cd Foo
           cd Foo.new
           cd @ivar
           cd ..
+          cd -
           cd
       HELP
 
       def execute(arg)
-        case arg
+        previous_workspace = irb_context.workspace
+
+        case arg.strip
         when ".."
           irb_context.pop_workspace
+        when "-"
+          irb_context.replace_workspace(irb_context.previous_workspace)
         when ""
           # TODO: decide what workspace commands should be kept, and underlying APIs should look like,
           # and perhaps add a new API to clear the workspace stack.
-          prev_workspace = irb_context.pop_workspace
-          while prev_workspace
-            prev_workspace = irb_context.pop_workspace
+          popped_workspace = irb_context.pop_workspace
+          while popped_workspace
+            popped_workspace = irb_context.pop_workspace
           end
         else
           begin
@@ -41,6 +49,8 @@ def execute(arg)
             warn "Error: #{e}"
           end
         end
+
+        irb_context.previous_workspace = previous_workspace
       end
     end
   end

lib/irb/context.rb

@@ -28,6 +28,8 @@ def initialize(irb, workspace = nil, input_method = nil)
       else
         @workspace_stack << WorkSpace.new
       end
+      # for cd command's `-` argument
+      @previous_workspace = workspace
       @thread = Thread.current
 
       # copy of default configuration
@@ -241,6 +243,8 @@ def workspace
       @workspace_stack.last
     end
 
+    attr_accessor :previous_workspace
+
     # Replace the current workspace with the given +workspace+.
     def replace_workspace(workspace)
       @workspace_stack.pop

test/irb/command/test_cd.rb

@@ -40,6 +40,44 @@ def test_cd
       assert_match(/irb\(Foo\):006>/, out)
     end
 
+    def test_dash_switches_between_the_last_two_contexts
+      out = run_ruby_file do
+        type "cd Foo"
+        type "cd Bar"
+        type "cd -"
+        type "cd -"
+        type "cd"
+        type "cd -"
+        type "cd -"
+        type "exit"
+      end
+
+      assert_match(/irb\(Foo::Bar\):003>/, out)
+      assert_match(/irb\(Foo\):004>/, out)
+      assert_match(/irb\(Foo::Bar\):005>/, out)
+      assert_match(/irb\(main\):006>/, out)
+      assert_match(/irb\(Foo::Bar\):007>/, out)
+      assert_match(/irb\(main\):008>/, out)
+
+      out = run_ruby_file do
+        type "cd -"
+        type "cd Foo"
+        type "cd -"
+        type "cd -"
+        type "cd Bar"
+        type "cd .."
+        type "cd -"
+        type "exit"
+      end
+
+      assert_match(/irb\(Foo\):003>/, out)
+      assert_match(/irb\(main\):004>/, out)
+      assert_match(/irb\(Foo\):005>/, out)
+      assert_match(/irb\(Foo::Bar\):006>/, out)
+      assert_match(/irb\(Foo\):007>/, out)
+      assert_match(/irb\(Foo::Bar\):008>/, out)
+    end
+
     def test_cd_moves_top_level_with_no_args
       out = run_ruby_file do
         type "cd Foo"