Don't restrict the DCH control code to only the current scroll region

Matches behavior of other terminal emulators.  Fixes #3090

docs/changelog.rst

@@ -44,6 +44,8 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Fix last character of URL not being detected if it is the only character on a
   new line (:iss:`3088`)
 
+- Don't restrict the DCH control code to only the current scroll region  (:iss:`3090`)
+
 
 0.19.1 [2020-10-06]
 -------------------

kitty/screen.c

@@ -1351,7 +1351,7 @@ screen_repeat_character(Screen *self, unsigned int count) {
 void
 screen_delete_characters(Screen *self, unsigned int count) {
     // Delete characters, later characters are moved left
-    unsigned int top = self->margin_top, bottom = self->margin_bottom;
+    const unsigned int top = 0, bottom = self->lines - 1;
     if (count == 0) count = 1;
     if (top <= self->cursor->y && self->cursor->y <= bottom) {
         unsigned int x = self->cursor->x;

kitty_tests/screen.py

@@ -142,6 +142,13 @@ class TestScreen(BaseTest):
         self.ae(str(s.line(0)), 'ade')
         self.assertTrue(s.line(0).cursor_from(4).bold)
         self.assertFalse(s.line(0).cursor_from(2).bold)
+        s = self.create_screen()
+        s.set_margins(1, 2)
+        s.cursor.y = 3
+        s.draw('abcde')
+        s.cursor.x = 0
+        s.delete_characters(2)
+        self.ae('cde', str(s.line(s.cursor.y)))
 
         init()
         s.erase_characters(2)