From e45697f78a97e700989d39fadc73129545f67597 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 31 Dec 2021 09:28:47 +0530
Subject: [PATCH] Fix a regression that broke rendering of unicode regional
 indicators

At some point, unicode regional indicators became combining chars in the
unicode standard, which broke the handling of them in draw_codepoint().
The fix has the added advantage of improving performance in the common
case by only checking for combining chars. The flag check happens only
if the first check matches.

Fixes #4407
---
 kitty/screen.c           | 13 +++++++------
 kitty_tests/datatypes.py |  4 +++-
 kitty_tests/screen.py    | 11 +++++++++++
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/kitty/screen.c b/kitty/screen.c
index 9295d4025..594b8028c 100644
--- a/kitty/screen.c
+++ b/kitty/screen.c
@@ -664,12 +664,13 @@ draw_codepoint(Screen *self, char_type och, bool from_input_stream) {
     uint32_t ch = och < 256 ? self->g_charset[och] : och;
     bool is_cc = is_combining_char(ch);
     if (UNLIKELY(is_cc)) {
-        draw_combining_char(self, ch);
-        return;
-    }
-    bool is_flag = is_flag_codepoint(ch);
-    if (UNLIKELY(is_flag)) {
-        if (draw_second_flag_codepoint(self, ch)) return;
+        bool is_flag = is_flag_codepoint(ch);
+        if (UNLIKELY(is_flag)) {
+            if (draw_second_flag_codepoint(self, ch)) return;
+        } else {
+            draw_combining_char(self, ch);
+            return;
+        }
     }
     int char_width = wcwidth_std(ch);
     if (UNLIKELY(char_width < 1)) {
diff --git a/kitty_tests/datatypes.py b/kitty_tests/datatypes.py
index 17e407b8c..d0128868f 100644
--- a/kitty_tests/datatypes.py
+++ b/kitty_tests/datatypes.py
@@ -383,8 +383,10 @@ def w(x):
         self.ae(wcswidth('\U0001F1E6\U0001F1E8\U0001F1E6'), 4)
         self.ae(wcswidth('a\u00adb'), 2)
         # Regional indicator symbols (unicode flags) are defined as having
-        # Emoji_Presentation so must have width 2
+        # Emoji_Presentation so must have width 2 but combined must have
+        # width 2 not 4
         self.ae(tuple(map(w, '\U0001f1ee\U0001f1f3')), (2, 2))
+        self.ae(wcswidth('\U0001f1ee\U0001f1f3'), 2)
         tpl = truncate_point_for_length
         self.ae(tpl('abc', 4), 3)
         self.ae(tpl('abc', 2), 2)
diff --git a/kitty_tests/screen.py b/kitty_tests/screen.py
index 3f874dc1b..5ed69d2c5 100644
--- a/kitty_tests/screen.py
+++ b/kitty_tests/screen.py
@@ -110,6 +110,17 @@ def test_emoji_skin_tone_modifiers(self):
         self.ae(str(s.line(0)), q)
         self.ae(s.cursor.x, 2)
 
+    def test_regional_indicators(self):
+        s = self.create_screen()
+        flag = '\U0001f1ee\U0001f1f3'
+        s.draw(flag)
+        self.ae(str(s.line(0)), flag)
+        self.ae(s.cursor.x, 2)
+        s = self.create_screen()
+        s.draw('a'), s.draw(flag[0]), s.draw('b')
+        self.ae(str(s.line(0)), 'a' + flag[0] + 'b')
+        self.ae(s.cursor.x, 4)
+
     def test_zwj(self):
         s = self.create_screen(cols=20)
         q = '\U0001f468\u200d\U0001f469\u200d\U0001f467\u200d\U0001f466'