Fix handling of tab character when cursor is at end of line and wrapping is enabled

Fixes #7250

docs/changelog.rst

@@ -62,6 +62,8 @@ Detailed list of changes
 
 - macOS: Fix a regression in the previous release that broke rendering of some symbols on some systems (:iss:`7249`)
 
+- Fix handling of tab character when cursor is at end of line and wrapping is enabled (:iss:`7250`)
+
 0.33.1 [2024-03-21]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

kitty/screen.c

@@ -730,7 +730,18 @@ draw_text_loop(Screen *self, const uint32_t *chars, size_t num_chars, text_loop_
                 case BS:
                     screen_backspace(self); break;
                 case HT:
-                    screen_tab(self); break;
+                    if (UNLIKELY(self->cursor->x >= self->columns)) {
+                        if (self->modes.mDECAWM) {
+                            // xterm discards the TAB in this case so match its behavior
+                            continue_to_next_line(self);
+                            init_text_loop_line(self, s);
+                        } else if (self->columns > 0){
+                            self->cursor->x = self->columns - 1;
+                            if (cursor_on_wide_char_trailer(self, s)) move_cursor_off_wide_char_trailer(self, s);
+                            screen_tab(self);
+                        }
+                    } else screen_tab(self);
+                    break;
                 case SI:
                     screen_change_charset(self, 0); break;
                 case SO:

kitty_tests/screen.py

@@ -419,6 +419,9 @@ def test_tab_stops(self):
             s.draw('*')
         s.cursor_position(2, 2)
         self.ae(str(s.line(0)), '\t*'*13)
+        s = self.create_screen(cols=4, lines=2)
+        s.draw('aaaX\tbbbb')
+        self.ae(str(s.line(0)) + str(s.line(1)), 'aaaXbbbb')
 
     def test_margins(self):
         # Taken from vttest/main.c