perf(theme): hex color parsing and formatting without substrings (#1541)

lib/core/theme/parser/color_parser.dart

@@ -1,34 +1,49 @@
 import 'dart:ui';
 
 /// Parses VS Code color strings into Flutter [Color].
+///
+/// Hex digits are read straight from the code units (no substring / `int.parse`
+/// per channel), so loading a theme with thousands of rules allocates nothing
+/// per color but the result.
 Color parseVsCodeColor(String input) {
-  var s = input.trim();
+  final s = input.trim();
   if (s.isEmpty) {
     throw const FormatException('Empty color string');
   }
-  if (s.startsWith('#')) {
-    s = s.substring(1);
-  }
-  if (s.length == 3) {
-    final r = s[0];
-    final g = s[1];
-    final b = s[2];
-    s = '$r$r$g$g$b$b';
-    return Color(int.parse('FF$s', radix: 16));
-  }
-  if (s.length == 4) {
-    final r = s[0];
-    final g = s[1];
-    final b = s[2];
-    final a = s[3];
-    s = '$r$r$g$g$b$b$a$a';
-    return _fromRgbaHex(s);
-  }
-  if (s.length == 6) {
-    return Color(int.parse('FF$s', radix: 16));
-  }
-  if (s.length == 8) {
-    return _fromRgbaHex(s);
+  final from = s.codeUnitAt(0) == 0x23 ? 1 : 0; // '#'
+  try {
+    switch (s.length - from) {
+      case 3: // RGB
+        return Color.fromARGB(
+          0xFF,
+          _nibble(s, from) * 17,
+          _nibble(s, from + 1) * 17,
+          _nibble(s, from + 2) * 17,
+        );
+      case 4: // RGBA
+        return Color.fromARGB(
+          _nibble(s, from + 3) * 17,
+          _nibble(s, from) * 17,
+          _nibble(s, from + 1) * 17,
+          _nibble(s, from + 2) * 17,
+        );
+      case 6: // RRGGBB
+        return Color.fromARGB(
+          0xFF,
+          _byte(s, from),
+          _byte(s, from + 2),
+          _byte(s, from + 4),
+        );
+      case 8: // RRGGBBAA
+        return Color.fromARGB(
+          _byte(s, from + 6),
+          _byte(s, from),
+          _byte(s, from + 2),
+          _byte(s, from + 4),
+        );
+    }
+  } on FormatException {
+    throw FormatException('Unsupported color format: $input');
   }
   throw FormatException('Unsupported color format: $input');
 }
@@ -51,11 +66,12 @@ Color parseQueryaThemeColor(String raw) {
 
   if (s.length == 8) {
     try {
-      final aa = int.parse(s.substring(0, 2), radix: 16);
-      final rr = int.parse(s.substring(2, 4), radix: 16);
-      final gg = int.parse(s.substring(4, 6), radix: 16);
-      final bb = int.parse(s.substring(6, 8), radix: 16);
-      return Color.fromARGB(aa, rr, gg, bb);
+      return Color.fromARGB(
+        _byte(s, 0),
+        _byte(s, 2),
+        _byte(s, 4),
+        _byte(s, 6),
+      );
     } on FormatException {
       throw FormatException('Invalid Querya theme color: $raw');
     }
@@ -70,30 +86,33 @@ Color parseQueryaThemeColor(String raw) {
 
 /// Encodes a [Color] as a VS Code hex string (`#RRGGBB` or `#RRGGBBAA`).
 String formatVsCodeColor(Color color) {
-  String channel(double component) => (component * 255.0)
-      .round()
-      .clamp(0, 255)
-      .toRadixString(16)
-      .padLeft(2, '0');
-  final rr = channel(color.r);
-  final gg = channel(color.g);
-  final bb = channel(color.b);
-  if (color.a < 1.0) {
-    final aa = channel(color.a);
-    return '#$rr$gg$bb$aa';
-  }
-  return '#$rr$gg$bb';
+  final withAlpha = color.a < 1.0;
+  final units = List<int>.filled(withAlpha ? 9 : 7, 0x23); // '#'
+  _writeHexByte(units, 1, _channel(color.r));
+  _writeHexByte(units, 3, _channel(color.g));
+  _writeHexByte(units, 5, _channel(color.b));
+  if (withAlpha) _writeHexByte(units, 7, _channel(color.a));
+  return String.fromCharCodes(units);
+}
+
+int _channel(double component) =>
+    (component * 255.0).round().clamp(0, 255);
+
+const String _hexChars = '0123456789abcdef';
+
+void _writeHexByte(List<int> out, int at, int value) {
+  out[at] = _hexChars.codeUnitAt(value >> 4);
+  out[at + 1] = _hexChars.codeUnitAt(value & 0xF);
 }
 
-Color _fromRgbaHex(String eight) {
-  final rr = eight.substring(0, 2);
-  final gg = eight.substring(2, 4);
-  final bb = eight.substring(4, 6);
-  final aa = eight.substring(6, 8);
-  return Color.fromARGB(
-    int.parse(aa, radix: 16),
-    int.parse(rr, radix: 16),
-    int.parse(gg, radix: 16),
-    int.parse(bb, radix: 16),
-  );
+/// The hex digit at [at] in [s], or a [FormatException].
+int _nibble(String s, int at) {
+  final c = s.codeUnitAt(at);
+  if (c >= 0x30 && c <= 0x39) return c - 0x30; // 0-9
+  if (c >= 0x61 && c <= 0x66) return c - 0x61 + 10; // a-f
+  if (c >= 0x41 && c <= 0x46) return c - 0x41 + 10; // A-F
+  throw FormatException('Invalid hex digit', s, at);
 }
+
+/// Two hex digits at [at] as one byte.
+int _byte(String s, int at) => (_nibble(s, at) << 4) | _nibble(s, at + 1);

test/core/theme/parser/color_parser_test.dart

@@ -100,4 +100,43 @@ void main() {
       );
     });
   });
+
+  group('hex scanner (#1541)', () {
+    test('4-digit shorthand is RGBA, each nibble doubled', () {
+      expect(parseVsCodeColor('#1234'), const Color(0x44112233));
+      expect(parseVsCodeColor('f08c'), const Color(0xCCFF0088));
+    });
+
+    test('8-digit VS Code value is RRGGBBAA, Querya value is AARRGGBB', () {
+      expect(parseVsCodeColor('#11223344'), const Color(0x44112233));
+      expect(parseQueryaThemeColor('#44112233'), const Color(0x44112233));
+    });
+
+    test('upper and lower case digits parse the same', () {
+      expect(parseVsCodeColor('#AbCdEf'), parseVsCodeColor('#abcdef'));
+      expect(parseVsCodeColor('#AbCdEf'), const Color(0xFFABCDEF));
+    });
+
+    test('signs, spaces and non-hex characters are rejected', () {
+      for (final bad in ['#+12345', '#-12345', '#12 456', '#12345g', '#zzz']) {
+        expect(() => parseVsCodeColor(bad), throwsFormatException,
+            reason: bad);
+      }
+      expect(() => parseQueryaThemeColor('+1234567'), throwsFormatException);
+    });
+
+    test('formatVsCodeColor writes lowercase hex and alpha only when needed',
+        () {
+      expect(formatVsCodeColor(const Color(0xFF000000)), '#000000');
+      expect(formatVsCodeColor(const Color(0xFF0A0B0C)), '#0a0b0c');
+      expect(formatVsCodeColor(const Color(0x80112233)), '#11223380');
+    });
+
+    test('every channel value round-trips through format and parse', () {
+      for (var v = 0; v < 256; v++) {
+        final c = Color.fromARGB(0xFF, v, 255 - v, v ^ 0x5A);
+        expect(parseVsCodeColor(formatVsCodeColor(c)), c, reason: 'v=$v');
+      }
+    });
+  });
 }