Use cursor-x-coordinate instead of byte_pointer in em_exchange_mark (#868)

Marked byte_position could be an invalid byte position when the marked line is edited.
Use cursor position and move to the nearest valid position instead.

Author: tompng

lib/reline/line_editor.rb

@@ -224,7 +224,7 @@ def eof?
 
   def reset_variables(prompt = '')
     @prompt = prompt.gsub("\n", "\\n")
-    @mark_pointer = nil
+    @mark_position = nil
     @is_multiline = false
     @finished = false
     @history_pointer = nil
@@ -2318,15 +2318,22 @@ def finish
   end
 
   private def em_set_mark(key)
-    @mark_pointer = [@byte_pointer, @line_index]
+    cursor_column = Reline::Unicode.calculate_width(current_line.byteslice(0, @byte_pointer))
+    @mark_position = [@line_index, cursor_column]
   end
   alias_method :set_mark, :em_set_mark
 
   private def em_exchange_mark(key)
-    return unless @mark_pointer
-    new_pointer = [@byte_pointer, @line_index]
-    @byte_pointer, @line_index = @mark_pointer
-    @mark_pointer = new_pointer
+    return unless @mark_position
+    line_index, cursor_column = @mark_position
+    em_set_mark(key)
+    if @buffer_of_lines.size <= line_index
+      @line_index = @buffer_of_lines.size - 1
+      @byte_pointer = current_line.bytesize
+    else
+      @line_index = line_index
+      calculate_nearest_cursor(cursor_column)
+    end
   end
   alias_method :exchange_point_and_mark, :em_exchange_mark
 

test/reline/test_key_actor_emacs.rb

@@ -1245,27 +1245,50 @@ def test_em_set_mark_and_em_exchange_mark
     assert_line_around_cursor('aaa bbb ccc ddd', '')
     input_keys("\C-a\eF\eF")
     assert_line_around_cursor('aaa bbb', ' ccc ddd')
-    assert_equal(nil, @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal(nil, @line_editor.instance_variable_get(:@mark_position))
     input_keys("\x00") # C-Space
     assert_line_around_cursor('aaa bbb', ' ccc ddd')
-    assert_equal([7, 0], @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal([0, 7], @line_editor.instance_variable_get(:@mark_position))
     input_keys("\C-a")
     assert_line_around_cursor('', 'aaa bbb ccc ddd')
-    assert_equal([7, 0], @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal([0, 7], @line_editor.instance_variable_get(:@mark_position))
     input_key_by_symbol(:em_exchange_mark)
     assert_line_around_cursor('aaa bbb', ' ccc ddd')
-    assert_equal([0, 0], @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal([0, 0], @line_editor.instance_variable_get(:@mark_position))
   end
 
   def test_em_exchange_mark_without_mark
     input_keys('aaa bbb ccc ddd')
     assert_line_around_cursor('aaa bbb ccc ddd', '')
     input_keys("\C-a\ef")
     assert_line_around_cursor('aaa', ' bbb ccc ddd')
-    assert_equal(nil, @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal(nil, @line_editor.instance_variable_get(:@mark_position))
     input_key_by_symbol(:em_exchange_mark)
     assert_line_around_cursor('aaa', ' bbb ccc ddd')
-    assert_equal(nil, @line_editor.instance_variable_get(:@mark_pointer))
+    assert_equal(nil, @line_editor.instance_variable_get(:@mark_position))
+  end
+
+  def test_em_exchange_mark_multibyte
+    input_keys("aaaaaaaaaaあああああ")
+    input_keys("\C-b\C-b")
+    assert_line_around_cursor('aaaaaaaaaaあああ', 'ああ')
+    input_keys("\x00") # C-Space
+    input_keys("\C-e\C-w")
+    input_keys("ああbbbbbああああああ")
+    input_key_by_symbol(:em_exchange_mark)
+    assert_line_around_cursor('ああbbbbbあああ', 'あああ')
+  end
+
+  def test_em_exchange_mark_line_disappear
+    input_key_by_symbol(:insert_multiline_text, char: "aaa\nbbb\nccc")
+    input_keys("\C-b\C-b")
+    input_keys("\x00") # C-Space
+    assert_line_around_cursor('c', 'cc')
+    input_keys("\C-a\C-h\C-p\C-a")
+    assert_line_around_cursor('', 'aaa')
+    input_key_by_symbol(:em_exchange_mark)
+    # If mark line does not exist, moves to the end of the input
+    assert_line_around_cursor('bbbccc', '')
   end
 
   def test_modify_lines_with_wrong_rs