[ruby/reline] Support ed_argument_digit by M+num

The vi mode can handle "argument number" before an operator or a motion,
such as, "3x" (equals "xxx"), and "3l" (equals "lll"). In the emacs
mode, GNU Readline can handle argument number with meta key, like
"Meta+3 x" (equals "xxx").

https://github.com/ruby/reline/commit/9183cc2e8b

lib/reline/line_editor.rb

@@ -2494,7 +2494,7 @@ class Reline::LineEditor
     end
   end
 
-  private def em_delete_prev_char(key)
+  private def em_delete_prev_char(key, arg: 1)
     if @is_multiline and @cursor == 0 and @line_index > 0
       @buffer_of_lines[@line_index] = @line
       @cursor = calculate_width(@buffer_of_lines[@line_index - 1])
@@ -2512,6 +2512,8 @@ class Reline::LineEditor
       @cursor -= width
       @cursor_max -= width
     end
+    arg -= 1
+    em_delete_prev_char(key, arg: arg) if arg > 0
   end
   alias_method :backward_delete_char, :em_delete_prev_char
 
@@ -3048,7 +3050,14 @@ class Reline::LineEditor
 
   private def ed_argument_digit(key)
     if @vi_arg.nil?
-      unless key.chr.to_i.zero?
+      if key.chr.to_i.zero?
+        if key.anybits?(0b10000000)
+          unescaped_key = key ^ 0b10000000
+          unless unescaped_key.chr.to_i.zero?
+            @vi_arg = unescaped_key.chr.to_i
+          end
+        end
+      else
         @vi_arg = key.chr.to_i
       end
     else

test/reline/test_key_actor_emacs.rb

@@ -2292,6 +2292,20 @@ class Reline::KeyActor::Emacs::Test < Reline::TestCase
     assert_cursor_max(2)
   end
 
+  def test_ed_argument_digit_by_meta_num
+    input_keys('abcdef')
+    assert_byte_pointer_size('abcdef')
+    assert_cursor(6)
+    assert_cursor_max(6)
+    assert_line('abcdef')
+    input_keys("\M-2", false)
+    input_keys("\C-h", false)
+    assert_byte_pointer_size('abcd')
+    assert_cursor(4)
+    assert_cursor_max(4)
+    assert_line('abcd')
+  end
+
   def test_input_unknown_char
     input_keys('͸') # U+0378 (unassigned)
     assert_line('͸')