From 1a32fb81914e954e06ebfa66ba4c00bbcc550e75 Mon Sep 17 00:00:00 2001
From: Harry Terkelsen <hterkelsen@users.noreply.github.com>
Date: Wed, 28 Sep 2022 16:35:56 -0700
Subject: [PATCH] Fix bug in binary search for font.contains
 (flutter/engine#36426)

---
 .../lib/src/engine/canvaskit/noto_font.dart   | 29 ++++---------------
 .../canvaskit/fallback_fonts_golden_test.dart | 29 +++++++++++++++++--
 2 files changed, 32 insertions(+), 26 deletions(-)

diff --git a/engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/noto_font.dart b/engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/noto_font.dart
index 83964c6f42..ad5b43e92a 100644
--- a/engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/noto_font.dart
+++ b/engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/noto_font.dart
@@ -37,33 +37,16 @@ class NotoFont {
     // is a range that contains the codeunit.
     int min = 0;
     int max = _rangeStarts.length - 1;
-    // Search for the first rangeStart that is greater than codeunit.
-    while (min < max) {
+    while (min <= max) {
       final int mid = (min + max) ~/ 2;
       if (_rangeStarts[mid] > codeUnit) {
-        if (mid == 0) {
-          final int rangeStart = _rangeStarts[mid];
-          final int rangeEnd = _rangeEnds[mid];
-          return rangeStart <= codeUnit && codeUnit <= rangeEnd;
-        }
-        final int rangeStart = _rangeStarts[mid - 1];
-        if (rangeStart <= codeUnit) {
-          final int rangeEnd = _rangeEnds[mid - 1];
-          return rangeStart <= codeUnit && codeUnit <= rangeEnd;
-        } else {
-          max = mid - 1;
-        }
-      } else if (_rangeStarts[mid] < codeUnit) {
-        // If this is the last index, check if the codeunit is contained within it.
-        if (mid == _rangeStarts.length) {
-          final int rangeStart = _rangeStarts[mid];
-          final int rangeEnd = _rangeEnds[mid];
-          return rangeStart <= codeUnit && codeUnit <= rangeEnd;
+        max = mid - 1;
+      } else {
+        // _rangeStarts[mid] <= codeUnit
+        if (_rangeEnds[mid] >= codeUnit) {
+          return true;
         }
         min = mid + 1;
-      } else {
-        // _rangeStarts[mid] == codeUnit
-        return true;
       }
     }
     return false;
diff --git a/engine/src/flutter/lib/web_ui/test/canvaskit/fallback_fonts_golden_test.dart b/engine/src/flutter/lib/web_ui/test/canvaskit/fallback_fonts_golden_test.dart
index 66ba97d7eb..84c05602b8 100644
--- a/engine/src/flutter/lib/web_ui/test/canvaskit/fallback_fonts_golden_test.dart
+++ b/engine/src/flutter/lib/web_ui/test/canvaskit/fallback_fonts_golden_test.dart
@@ -199,6 +199,31 @@ void testMain() {
       expect(loggingDownloader.log, isEmpty);
     });
 
+    test('can find glyph for 2/3 symbol', () async {
+      final Rasterizer rasterizer = CanvasKitRenderer.instance.rasterizer;
+      final LoggingDownloader loggingDownloader =
+          LoggingDownloader(NotoDownloader());
+      notoDownloadQueue.downloader = loggingDownloader;
+      // Try rendering text that requires fallback fonts, initially before the fonts are loaded.
+
+      CkParagraphBuilder(CkParagraphStyle()).addText('⅔');
+      rasterizer.debugRunPostFrameCallbacks();
+      await notoDownloadQueue.debugWhenIdle();
+      expect(
+        loggingDownloader.log,
+        <String>[
+          'Noto Sans',
+        ],
+      );
+
+      // Do the same thing but this time with loaded fonts.
+      loggingDownloader.log.clear();
+      CkParagraphBuilder(CkParagraphStyle()).addText('⅔');
+      rasterizer.debugRunPostFrameCallbacks();
+      await notoDownloadQueue.debugWhenIdle();
+      expect(loggingDownloader.log, isEmpty);
+    });
+
     test('findMinimumFontsForCodeunits for all supported code units', () async {
       final LoggingDownloader loggingDownloader =
           LoggingDownloader(NotoDownloader());
@@ -213,9 +238,7 @@ void testMain() {
       for (final NotoFont font in notoTree.root.enumerateAllElements()) {
         testedFonts.add(font.name);
         for (final CodeunitRange range in font.computeUnicodeRanges()) {
-          for (int codeUnit = range.start;
-              codeUnit < range.end;
-              codeUnit += 1) {
+          for (int codeUnit = range.start; codeUnit < range.end; codeUnit++) {
             supportedUniqueCodeUnits.add(codeUnit);
           }
         }