From 7f0674ac277c9e39977af1dd1887883c1ad78e24 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 7 Sep 2018 10:08:25 +0530
Subject: [PATCH] Fix backspacing of wide characters in wide-character unaware
 programs not working

Fixes #875
---
 docs/changelog.rst    |  2 ++
 kitty/screen.c        | 10 +++++++++-
 kitty_tests/screen.py |  9 +++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 3190ee57e..7b39358b8 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -13,6 +13,8 @@ Changelog
   font fallback for all subsequent characters that cannot be rendered in the
   main font to fail (:iss:`799`)
 
+- Fix backspacing of wide characters in wide-character unaware programs not working (:iss:`875`)
+
 - Linux: Fix number pad arrow keys not working when Numlock is off (:iss:`857`)
 
 - Wayland: Implement support for clipboard copy/paste (:iss:`855`)
diff --git a/kitty/screen.c b/kitty/screen.c
index 0000f5e36..872eed784 100644
--- a/kitty/screen.c
+++ b/kitty/screen.c
@@ -708,7 +708,15 @@ screen_is_cursor_visible(Screen *self) {
 
 void
 screen_backspace(Screen *self) {
-    screen_cursor_back(self, 1, -1);
+    unsigned int amount = 1;
+    if (self->cursor->x < self->columns && self->cursor->x > 1) {
+        // check if previous character is a wide character
+        linebuf_init_line(self->linebuf, self->cursor->y);
+        unsigned int xpos = self->cursor->x - 2;
+        GPUCell *gpu_cell = self->linebuf->line->gpu_cells + xpos;
+        if ((gpu_cell->attrs & WIDTH_MASK) == 2) amount = 2;
+    }
+    screen_cursor_back(self, amount, -1);
 }
 
 void
diff --git a/kitty_tests/screen.py b/kitty_tests/screen.py
index dc96c8068..ed35559be 100644
--- a/kitty_tests/screen.py
+++ b/kitty_tests/screen.py
@@ -222,6 +222,15 @@ class TestScreen(BaseTest):
         for i in range(1, 5):
             self.ae(str(s.line(i)), '12345')
 
+    def test_backspace_wide_characters(self):
+        s = self.create_screen()
+        s.draw('⛅')
+        self.ae(s.cursor.x, 2)
+        s.backspace()
+        s.draw(' ')
+        s.backspace()
+        self.ae(s.cursor.x, 0)
+
     def test_resize(self):
         s = self.create_screen(scrollback=6)
         s.draw(''.join([str(i) * s.columns for i in range(s.lines)]))