From 14b46188b539adc78bb29f6a9f07f53b32e8a40e Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Wed, 8 May 2024 21:09:30 +0900
Subject: [PATCH 1/7] Refactor send

---
 lib/reline/line_editor.rb | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 4c76932c10..79a250024c 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -948,7 +948,8 @@ def dialog_proc_scope_completion_journey_data
         unless @waiting_proc
           byte_pointer_diff = @byte_pointer - old_byte_pointer
           @byte_pointer = old_byte_pointer
-          send(@vi_waiting_operator, byte_pointer_diff)
+          method_obj = method(@vi_waiting_operator)
+          wrap_method_call(@vi_waiting_operator, method_obj, byte_pointer_diff)
           cleanup_waiting
         end
       else
@@ -1009,7 +1010,8 @@ def wrap_method_call(method_symbol, method_obj, key, with_operator = false)
       if @vi_waiting_operator
         byte_pointer_diff = @byte_pointer - old_byte_pointer
         @byte_pointer = old_byte_pointer
-        send(@vi_waiting_operator, byte_pointer_diff)
+        method_obj = method(@vi_waiting_operator)
+        wrap_method_call(@vi_waiting_operator, method_obj, byte_pointer_diff)
         cleanup_waiting
       end
       @kill_ring.process

From 9f09d8fb547a70b2d53e792b630d9c89fa9587d7 Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Fri, 10 May 2024 04:43:01 +0900
Subject: [PATCH 2/7] Implement the undo command

---
 lib/reline.rb                               |  2 +
 lib/reline/key_actor/emacs.rb               |  2 +-
 lib/reline/line_editor.rb                   | 82 ++++++++++++++++++++-
 test/reline/test_key_actor_emacs.rb         | 57 ++++++++++++++
 test/reline/yamatanooroti/test_rendering.rb | 12 +++
 5 files changed, 151 insertions(+), 4 deletions(-)

diff --git a/lib/reline.rb b/lib/reline.rb
index fb00b96531..61b819fa40 100644
--- a/lib/reline.rb
+++ b/lib/reline.rb
@@ -353,9 +353,11 @@ def readline(prompt = '', add_hist = false)
             line_editor.set_pasting_state(io_gate.in_pasting?)
             inputs.each do |key|
               if key.char == :bracketed_paste_start
+                line_editor.save_old_buffer
                 text = io_gate.read_bracketed_paste
                 line_editor.insert_pasted_text(text)
                 line_editor.scroll_into_view
+                line_editor.save_past_lines
               else
                 line_editor.update(key)
               end
diff --git a/lib/reline/key_actor/emacs.rb b/lib/reline/key_actor/emacs.rb
index 9c797ba43e..edd88289a3 100644
--- a/lib/reline/key_actor/emacs.rb
+++ b/lib/reline/key_actor/emacs.rb
@@ -63,7 +63,7 @@ class Reline::KeyActor::Emacs < Reline::KeyActor::Base
     #  30 ^^
     :ed_unassigned,
     #  31 ^_
-    :ed_unassigned,
+    :undo,
     #  32 SPACE
     :ed_insert,
     #  33 !
diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 79a250024c..3b4d377ee7 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -4,7 +4,6 @@
 require 'tempfile'
 
 class Reline::LineEditor
-  # TODO: undo
   # TODO: Use "private alias_method" idiom after drop Ruby 2.5.
   attr_reader :byte_pointer
   attr_accessor :confirm_multiline_termination_proc
@@ -35,6 +34,31 @@ class Reline::LineEditor
     vi_end_big_word
   }
 
+  DELETE_COMMANDS = %i{
+    backward_delete_char
+    backward_kill_word
+    delete_char
+    ed_delete_next_char
+    ed_delete_prev_char
+    ed_delete_prev_word
+    ed_kill_line
+    em_delete
+    em_delete_next_word
+    em_delete_prev_char
+    em_kill_line
+    em_kill_region
+    kill_line
+    kill_whole_line
+    kill_word
+    unix_line_discard
+    unix_word_rubout
+    vi_change_to_eol
+    vi_delete_meta
+    vi_delete_meta_confirm
+    vi_delete_prev_char
+    vi_kill_line_prev
+  }
+
   module CompletionState
     NORMAL = :normal
     COMPLETION = :completion
@@ -251,6 +275,8 @@ def reset_variables(prompt = '', encoding:)
     @resized = false
     @cache = {}
     @rendered_screen = RenderedScreen.new(base_y: 0, lines: [], cursor_y: 0)
+    @past_lines = [["", 0, 0]]
+    @using_delete_command = false
     reset_line
   end
 
@@ -974,6 +1000,9 @@ def dialog_proc_scope_completion_journey_data
   end
 
   def wrap_method_call(method_symbol, method_obj, key, with_operator = false)
+    if DELETE_COMMANDS.include?(method_symbol)
+      @using_delete_command = true
+    end
     if @config.editing_mode_is?(:emacs, :vi_insert) and @vi_waiting_operator.nil?
       not_insertion = method_symbol != :ed_insert
       process_insert(force: not_insertion)
@@ -1108,6 +1137,7 @@ def update(key)
   end
 
   def input_key(key)
+    save_old_buffer
     @config.reset_oneshot_key_bindings
     @dialogs.each do |dialog|
       if key.char.instance_of?(Symbol) and key.char == dialog.name
@@ -1122,7 +1152,6 @@ def input_key(key)
       finish
       return
     end
-    old_lines = @buffer_of_lines.dup
     @first_char = false
     @completion_occurs = false
 
@@ -1136,12 +1165,14 @@ def input_key(key)
       @completion_journey_state = nil
     end
 
+    save_past_lines
+
     if @in_pasting
       clear_dialogs
       return
     end
 
-    modified = old_lines != @buffer_of_lines
+    modified = @old_buffer_of_lines != @buffer_of_lines
     if !@completion_occurs && modified && !@config.disable_completion && @config.autocompletion
       # Auto complete starts only when edited
       process_insert(force: true)
@@ -1150,6 +1181,31 @@ def input_key(key)
     modified
   end
 
+  def save_old_buffer
+    @old_buffer_of_lines = @buffer_of_lines.dup
+    @old_byte_pointer = @byte_pointer.dup
+    @old_line_index = @line_index.dup
+  end
+
+  MAX_PAST_LINES = 100
+  def save_past_lines
+    if @old_buffer_of_lines != @buffer_of_lines
+      if !@using_delete_command && @buffer_of_lines == @past_lines.last.first
+        # When deleting, @buffer_of_lines and @past_lines.last.first become the same.
+        # If it is the same as the previous state, consider it undone and do not add to past_lines.
+        @past_lines.pop
+      else
+        # Save the state before the changes.
+        @past_lines.push([@old_buffer_of_lines, @old_byte_pointer, @old_line_index])
+      end
+    end
+    @using_delete_command = false
+
+    if @past_lines.size > MAX_PAST_LINES
+      @past_lines.shift
+    end
+  end
+
   def scroll_into_view
     _wrapped_cursor_x, wrapped_cursor_y = wrapped_cursor_position
     if wrapped_cursor_y < screen_scroll_top
@@ -1226,6 +1282,18 @@ def set_current_line(line, byte_pointer = nil)
     process_auto_indent
   end
 
+  def set_current_lines(lines, byte_pointer = nil, line_index = 0)
+    cursor = current_byte_pointer_cursor
+    @buffer_of_lines = lines
+    @line_index = line_index
+    if byte_pointer
+      @byte_pointer = byte_pointer
+    else
+      calculate_nearest_cursor(cursor)
+    end
+    process_auto_indent
+  end
+
   def retrieve_completion_block(set_completion_quote_character = false)
     if Reline.completer_word_break_characters.empty?
       word_break_regexp = nil
@@ -1915,6 +1983,7 @@ def finish
 
   private def em_delete_or_list(key)
     if current_line.empty? or @byte_pointer < current_line.bytesize
+      @using_delete_command = true
       em_delete(key)
     elsif !@config.autocompletion # show completed list
       result = call_completion_proc
@@ -2489,4 +2558,11 @@ def finish
   private def vi_editing_mode(key)
     @config.editing_mode = :vi_insert
   end
+
+  private def undo(_key)
+    return if @past_lines.empty?
+
+    target_lines, target_cursor_x, target_cursor_y = @past_lines.last
+    set_current_lines(target_lines, target_cursor_x, target_cursor_y)
+  end
 end
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index 409a7334cb..c2c79e068f 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -1437,4 +1437,61 @@ def test_vi_editing_mode
     @line_editor.__send__(:vi_editing_mode, nil)
     assert(@config.editing_mode_is?(:vi_insert))
   end
+
+  def test_undo
+    input_keys("aあb\C-h\C-h\C-h", false)
+    assert_line_around_cursor('', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('a', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('aあ', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('aあb', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('aあ', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('a', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('', '')
+  end
+
+  def test_undo_with_cursor_position
+    input_keys("abc\C-b\C-h", false)
+    assert_line_around_cursor('a', 'c')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('ab', 'c')
+    input_keys("あいう\C-b\C-h", false)
+    assert_line_around_cursor('abあ', 'うc')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('abあい', 'うc')
+  end
+
+  def test_undo_with_multiline
+    @line_editor.multiline_on
+    @line_editor.confirm_multiline_termination_proc = proc {}
+    input_keys("1\n2\n3", false)
+    assert_whole_lines(["1", "2", "3"])
+    assert_line_index(2)
+    assert_line_around_cursor('3', '')
+    input_keys("\C-p\C-h\C-h", false)
+    assert_whole_lines(["1", "3"])
+    assert_line_index(0)
+    assert_line_around_cursor('1', '')
+    input_keys("\C-_", false)
+    assert_whole_lines(["1", "", "3"])
+    assert_line_index(1)
+    assert_line_around_cursor('', '')
+    input_keys("\C-_", false)
+    assert_whole_lines(["1", "2", "3"])
+    assert_line_index(1)
+    assert_line_around_cursor('2', '')
+    input_keys("\C-_", false)
+    assert_whole_lines(["1", "2", ""])
+    assert_line_index(2)
+    assert_line_around_cursor('', '')
+    input_keys("\C-_", false)
+    assert_whole_lines(["1", "2"])
+    assert_line_index(1)
+    assert_line_around_cursor('2', '')
+  end
 end
diff --git a/test/reline/yamatanooroti/test_rendering.rb b/test/reline/yamatanooroti/test_rendering.rb
index 9e8d7da78f..b23701c6a5 100644
--- a/test/reline/yamatanooroti/test_rendering.rb
+++ b/test/reline/yamatanooroti/test_rendering.rb
@@ -556,6 +556,18 @@ def test_bracketed_paste
       EOC
     end
 
+    def test_bracketed_paste_with_undo
+      omit if Reline.core.io_gate.win?
+      start_terminal(5, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl}, startup_message: 'Multiline REPL.')
+      write("\e[200~def hoge\r\t3\rend\e[201~")
+      write("\C-_")
+      close
+      assert_screen(<<~EOC)
+        Multiline REPL.
+        prompt>
+      EOC
+    end
+
     def test_backspace_until_returns_to_initial
       start_terminal(5, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl}, startup_message: 'Multiline REPL.')
       write("ABC")

From 3f18434c74dbbc150caba3cdce587f881174e2f9 Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Sat, 11 May 2024 23:20:40 +0900
Subject: [PATCH 3/7] Fix @past_lines initialization

---
 lib/reline/line_editor.rb           | 4 ++--
 test/reline/test_key_actor_emacs.rb | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 3b4d377ee7..02e46c06be 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -275,7 +275,7 @@ def reset_variables(prompt = '', encoding:)
     @resized = false
     @cache = {}
     @rendered_screen = RenderedScreen.new(base_y: 0, lines: [], cursor_y: 0)
-    @past_lines = [["", 0, 0]]
+    @past_lines = []
     @using_delete_command = false
     reset_line
   end
@@ -1190,7 +1190,7 @@ def save_old_buffer
   MAX_PAST_LINES = 100
   def save_past_lines
     if @old_buffer_of_lines != @buffer_of_lines
-      if !@using_delete_command && @buffer_of_lines == @past_lines.last.first
+      if !@past_lines.empty? && !@using_delete_command && @buffer_of_lines == @past_lines.last.first
         # When deleting, @buffer_of_lines and @past_lines.last.first become the same.
         # If it is the same as the previous state, consider it undone and do not add to past_lines.
         @past_lines.pop
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index c2c79e068f..d79b0a60e8 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -1439,6 +1439,8 @@ def test_vi_editing_mode
   end
 
   def test_undo
+    input_keys("\C-_", false)
+    assert_line_around_cursor('', '')
     input_keys("aあb\C-h\C-h\C-h", false)
     assert_line_around_cursor('', '')
     input_keys("\C-_", false)

From f794c84339e89ca6e958961ffad3d7f8ab28d83b Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Sat, 11 May 2024 23:27:31 +0900
Subject: [PATCH 4/7] Improve assertion

---
 test/reline/yamatanooroti/test_rendering.rb | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/test/reline/yamatanooroti/test_rendering.rb b/test/reline/yamatanooroti/test_rendering.rb
index b23701c6a5..37a1c1a193 100644
--- a/test/reline/yamatanooroti/test_rendering.rb
+++ b/test/reline/yamatanooroti/test_rendering.rb
@@ -559,12 +559,13 @@ def test_bracketed_paste
     def test_bracketed_paste_with_undo
       omit if Reline.core.io_gate.win?
       start_terminal(5, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl}, startup_message: 'Multiline REPL.')
+      write("abc")
       write("\e[200~def hoge\r\t3\rend\e[201~")
       write("\C-_")
       close
       assert_screen(<<~EOC)
         Multiline REPL.
-        prompt>
+        prompt> abc
       EOC
     end
 

From 98907fc55636ffd4fc357d00408601be36322a52 Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Sun, 12 May 2024 00:51:20 +0900
Subject: [PATCH 5/7] Hide to save buffer in insert_pasted_text

---
 lib/reline.rb             | 2 --
 lib/reline/line_editor.rb | 2 ++
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/reline.rb b/lib/reline.rb
index 61b819fa40..fb00b96531 100644
--- a/lib/reline.rb
+++ b/lib/reline.rb
@@ -353,11 +353,9 @@ def readline(prompt = '', add_hist = false)
             line_editor.set_pasting_state(io_gate.in_pasting?)
             inputs.each do |key|
               if key.char == :bracketed_paste_start
-                line_editor.save_old_buffer
                 text = io_gate.read_bracketed_paste
                 line_editor.insert_pasted_text(text)
                 line_editor.scroll_into_view
-                line_editor.save_past_lines
               else
                 line_editor.update(key)
               end
diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 02e46c06be..1b054a91b4 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -1376,6 +1376,7 @@ def confirm_multiline_termination
   end
 
   def insert_pasted_text(text)
+    save_old_buffer
     pre = @buffer_of_lines[@line_index].byteslice(0, @byte_pointer)
     post = @buffer_of_lines[@line_index].byteslice(@byte_pointer..)
     lines = (pre + text.gsub(/\r\n?/, "\n") + post).split("\n", -1)
@@ -1383,6 +1384,7 @@ def insert_pasted_text(text)
     @buffer_of_lines[@line_index, 1] = lines
     @line_index += lines.size - 1
     @byte_pointer = @buffer_of_lines[@line_index].bytesize - post.bytesize
+    save_past_lines
   end
 
   def insert_text(text)

From 9a19266eb0dcab2319ddbc5fa4207a9cd2d4969f Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Mon, 13 May 2024 00:58:53 +0900
Subject: [PATCH 6/7] Replace @using_delete_command with @undoing

---
 lib/reline/line_editor.rb | 38 ++++----------------------------------
 1 file changed, 4 insertions(+), 34 deletions(-)

diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 1b054a91b4..7afe354e4d 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -34,31 +34,6 @@ class Reline::LineEditor
     vi_end_big_word
   }
 
-  DELETE_COMMANDS = %i{
-    backward_delete_char
-    backward_kill_word
-    delete_char
-    ed_delete_next_char
-    ed_delete_prev_char
-    ed_delete_prev_word
-    ed_kill_line
-    em_delete
-    em_delete_next_word
-    em_delete_prev_char
-    em_kill_line
-    em_kill_region
-    kill_line
-    kill_whole_line
-    kill_word
-    unix_line_discard
-    unix_word_rubout
-    vi_change_to_eol
-    vi_delete_meta
-    vi_delete_meta_confirm
-    vi_delete_prev_char
-    vi_kill_line_prev
-  }
-
   module CompletionState
     NORMAL = :normal
     COMPLETION = :completion
@@ -276,7 +251,7 @@ def reset_variables(prompt = '', encoding:)
     @cache = {}
     @rendered_screen = RenderedScreen.new(base_y: 0, lines: [], cursor_y: 0)
     @past_lines = []
-    @using_delete_command = false
+    @undoing = false
     reset_line
   end
 
@@ -1000,9 +975,6 @@ def dialog_proc_scope_completion_journey_data
   end
 
   def wrap_method_call(method_symbol, method_obj, key, with_operator = false)
-    if DELETE_COMMANDS.include?(method_symbol)
-      @using_delete_command = true
-    end
     if @config.editing_mode_is?(:emacs, :vi_insert) and @vi_waiting_operator.nil?
       not_insertion = method_symbol != :ed_insert
       process_insert(force: not_insertion)
@@ -1190,16 +1162,14 @@ def save_old_buffer
   MAX_PAST_LINES = 100
   def save_past_lines
     if @old_buffer_of_lines != @buffer_of_lines
-      if !@past_lines.empty? && !@using_delete_command && @buffer_of_lines == @past_lines.last.first
-        # When deleting, @buffer_of_lines and @past_lines.last.first become the same.
-        # If it is the same as the previous state, consider it undone and do not add to past_lines.
+      if !@past_lines.empty? && @undoing
         @past_lines.pop
       else
         # Save the state before the changes.
         @past_lines.push([@old_buffer_of_lines, @old_byte_pointer, @old_line_index])
       end
     end
-    @using_delete_command = false
+    @undoing = false
 
     if @past_lines.size > MAX_PAST_LINES
       @past_lines.shift
@@ -1985,7 +1955,6 @@ def finish
 
   private def em_delete_or_list(key)
     if current_line.empty? or @byte_pointer < current_line.bytesize
-      @using_delete_command = true
       em_delete(key)
     elsif !@config.autocompletion # show completed list
       result = call_completion_proc
@@ -2564,6 +2533,7 @@ def finish
   private def undo(_key)
     return if @past_lines.empty?
 
+    @undoing = true
     target_lines, target_cursor_x, target_cursor_y = @past_lines.last
     set_current_lines(target_lines, target_cursor_x, target_cursor_y)
   end

From 7b648bf2766f8c3939f3754e92413bb4fe8f9315 Mon Sep 17 00:00:00 2001
From: Mari Imaizumi <mariimaizumi5@gmail.com>
Date: Tue, 14 May 2024 02:56:59 +0900
Subject: [PATCH 7/7] Refactor `@past_lines`

---
 lib/reline/line_editor.rb           | 23 ++++++++++++-----------
 test/reline/test_key_actor_emacs.rb |  9 +++++++++
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index 7afe354e4d..23ece60220 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -1137,7 +1137,8 @@ def input_key(key)
       @completion_journey_state = nil
     end
 
-    save_past_lines
+    push_past_lines unless @undoing
+    @undoing = false
 
     if @in_pasting
       clear_dialogs
@@ -1159,18 +1160,15 @@ def save_old_buffer
     @old_line_index = @line_index.dup
   end
 
-  MAX_PAST_LINES = 100
-  def save_past_lines
+  def push_past_lines
     if @old_buffer_of_lines != @buffer_of_lines
-      if !@past_lines.empty? && @undoing
-        @past_lines.pop
-      else
-        # Save the state before the changes.
-        @past_lines.push([@old_buffer_of_lines, @old_byte_pointer, @old_line_index])
-      end
+      @past_lines.push([@old_buffer_of_lines, @old_byte_pointer, @old_line_index])
     end
-    @undoing = false
+    trim_past_lines
+  end
 
+  MAX_PAST_LINES = 100
+  def trim_past_lines
     if @past_lines.size > MAX_PAST_LINES
       @past_lines.shift
     end
@@ -1354,7 +1352,7 @@ def insert_pasted_text(text)
     @buffer_of_lines[@line_index, 1] = lines
     @line_index += lines.size - 1
     @byte_pointer = @buffer_of_lines[@line_index].bytesize - post.bytesize
-    save_past_lines
+    push_past_lines
   end
 
   def insert_text(text)
@@ -2534,7 +2532,10 @@ def finish
     return if @past_lines.empty?
 
     @undoing = true
+
     target_lines, target_cursor_x, target_cursor_y = @past_lines.last
     set_current_lines(target_lines, target_cursor_x, target_cursor_y)
+
+    @past_lines.pop
   end
 end
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index d79b0a60e8..013ca2f7b3 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -1496,4 +1496,13 @@ def test_undo_with_multiline
     assert_line_index(1)
     assert_line_around_cursor('2', '')
   end
+
+  def test_undo_with_many_times
+    str = "a" + "b" * 100
+    input_keys(str, false)
+    100.times { input_keys("\C-_", false) }
+    assert_line_around_cursor('a', '')
+    input_keys("\C-_", false)
+    assert_line_around_cursor('a', '')
+  end
 end