From e646596c5bacfe86d14f01ecadcf38378ff8a0c7 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 20 Mar 2024 20:01:17 +0530
Subject: [PATCH] macOS: When CoreText fails to find a fallback font for a
 character in the first Private Use Unicode Area, preferentially use the NERD
 font, if available, for it

Fixes #6043
---
 docs/changelog.rst |  3 +++
 kitty/core_text.m  | 46 +++++++++++++++++++++++++++-------------------
 2 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index dab909f38..da83cdf11 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -56,6 +56,9 @@ Detailed list of changes
 
 - macOS: Fix text rendered with fallback fonts not respecting bold/italic styling (:disc:`7241`)
 
+- macOS: When CoreText fails to find a fallback font for a character in the first Private Use Unicode Area, preferentially use the NERD font, if available, for it (:iss:`6043`)
+
+
 0.33.0 [2024-03-12]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/kitty/core_text.m b/kitty/core_text.m
index ff8af760e..e3ebd24cb 100644
--- a/kitty/core_text.m
+++ b/kitty/core_text.m
@@ -184,12 +184,17 @@ glyph_id_for_codepoint_ctfont(CTFontRef ct_font, char_type ch) {
     return glyphs[0];
 }
 
+static bool
+cf_string_equals(CFStringRef a, CFStringRef b) { return CFStringCompare(a, b, 0) == kCFCompareEqualTo; }
+
+#define LAST_RESORT_FONT_NAME "LastResort"
+
 static bool
 is_last_resort_font(CTFontRef new_font) {
     CFStringRef name = CTFontCopyPostScriptName(new_font);
-    CFComparisonResult cr = CFStringCompare(name, CFSTR("LastResort"), 0);
+    bool ans = cf_string_equals(name, CFSTR(LAST_RESORT_FONT_NAME));
     CFRelease(name);
-    return cr == kCFCompareEqualTo;
+    return ans;
 }
 
 static CTFontRef
@@ -197,26 +202,29 @@ manually_search_fallback_fonts(CTFontRef current_font, CPUCell *cell) {
     CFArrayRef fonts = CTFontCollectionCreateMatchingFontDescriptors(all_fonts_collection());
     CTFontRef ans = NULL;
     const CFIndex count = CFArrayGetCount(fonts);
+    char_type ch = cell->ch ? cell->ch : ' ';
+    bool in_first_pua = 0xe000 <= ch && ch <= 0xf8ff;
+    // preferentially load from NERD fonts
     for (CFIndex i = 0; i < count; i++) {
         CTFontDescriptorRef descriptor = (CTFontDescriptorRef)CFArrayGetValueAtIndex(fonts, i);
+        CFStringRef name = CTFontDescriptorCopyAttribute(descriptor, kCTFontNameAttribute);
+        bool is_last_resort_font = cf_string_equals(name, CFSTR(LAST_RESORT_FONT_NAME));
+        bool is_nerd_font = cf_string_equals(name, CFSTR("SymbolsNFM"));
+        CFRelease(name);
+        if (is_last_resort_font) continue;
         CTFontRef new_font = CTFontCreateWithFontDescriptor(descriptor, CTFontGetSize(current_font), NULL);
-        if (new_font) {
-            if (!is_last_resort_font(new_font)) {
-                char_type ch = cell->ch ? cell->ch : ' ';
-                bool found = true;
-                if (!glyph_id_for_codepoint_ctfont(new_font, ch)) found = false;
-                for (unsigned i = 0; i < arraysz(cell->cc_idx) && cell->cc_idx[i] && found; i++) {
-                    ch = codepoint_for_mark(cell->cc_idx[i]);
-                    if (!glyph_id_for_codepoint_ctfont(new_font, ch)) found = false;
-                }
-                if (found) {
-                    ans = new_font;
-                    if (global_state.debug_font_fallback) fprintf(stderr, "Manually found fallback font.\n");
-                    break;
-                }
-            }
-            CFRelease(new_font);
+        bool found = true;
+        if (!glyph_id_for_codepoint_ctfont(new_font, ch)) found = false;
+        for (unsigned i = 0; i < arraysz(cell->cc_idx) && cell->cc_idx[i] && found; i++) {
+            char_type cch = codepoint_for_mark(cell->cc_idx[i]);
+            if (!glyph_id_for_codepoint_ctfont(new_font, cch)) found = false;
         }
+        if (found) {
+            // preferentially use NERD font for glyphs in first PUA
+            if (!ans || is_nerd_font) { if (ans) CFRelease(ans); ans = new_font; CFRetain(ans); }
+            if (is_nerd_font || !in_first_pua) break;
+        }
+        CFRelease(new_font);
     }
     CFRelease(fonts);
     return ans;
@@ -241,7 +249,7 @@ find_substitute_face(CFStringRef str, CTFontRef old_font, CPUCell *cpu_cell) {
                 new_font = manually_search_fallback_fonts(old_font, cpu_cell);
                 if (new_font) return new_font;
             }
-            PyErr_Format(PyExc_ValueError, "Failed to find fallback CTFont other than the LastResort font for: %s", [(NSString *)str UTF8String]);
+            PyErr_Format(PyExc_ValueError, "Failed to find fallback CTFont other than the %s font for: %s", LAST_RESORT_FONT_NAME, [(NSString *)str UTF8String]);
             return NULL;
         }
         return new_font;