Update for oklab() tests

lib/src/functions/color.dart

@@ -476,11 +476,12 @@ final module = BuiltInModule("color", functions: <Callable>[
 
     var channelInfo = color.space.channels[channelIndex];
     var channelValue = color.channels[channelIndex];
+    var unit = channelInfo.associatedUnit;
+    if (unit == '%') {
+      channelValue = channelValue * 100 / (channelInfo as LinearChannel).max;
+    }
 
-    return channelInfo is LinearChannel
-        ? SassNumber(channelValue,
-            channelInfo.min == 0 && channelInfo.max == 100 ? '%' : null)
-        : SassNumber(channelValue, 'deg');
+    return SassNumber(channelValue, unit);
   }),
 
   _function("same", r"$color1, $color2", (arguments) {
@@ -1198,7 +1199,8 @@ Value _parseChannels(String functionName, Value input,
           var channelName =
               space?.channels[channels.indexOf(channel)].name ?? 'channel';
           throw SassScriptException(
-              'Expected $channelName $channel to be a number.', name);
+              'Expected $channelName channel to be a number, was $channel.',
+              name);
         }
       }
 
@@ -1346,14 +1348,15 @@ SassColor _colorFromChannels(ColorSpace space, SassNumber? channel0,
           alpha,
           fromRgbFunction ? ColorFormat.rgbFunction : null);
 
-    case ColorSpace.lab:
-    case ColorSpace.lch:
-    case ColorSpace.oklab:
-    case ColorSpace.oklch:
+    case ColorSpace.lab ||
+          ColorSpace.lch ||
+          ColorSpace.oklab ||
+          ColorSpace.oklch:
       return SassColor.forSpaceInternal(
           space,
-          _channelFromValue(space.channels[0], channel0)
-              .andThen((lightness) => fuzzyClamp(lightness, 0, 100)),
+          _channelFromValue(space.channels[0], channel0).andThen((lightness) =>
+              fuzzyClamp(
+                  lightness, 0, (space.channels[0] as LinearChannel).max)),
           _channelFromValue(space.channels[1], channel1),
           _channelFromValue(space.channels[2], channel2),
           alpha);

lib/src/value/color.dart

@@ -531,7 +531,8 @@ class SassColor extends Value {
       return SassColor.forSpaceInternal(
           space,
           clampChannel0
-              ? channels[0].andThen((value) => fuzzyClamp(value, 0, 100))
+              ? channels[0].andThen((value) => fuzzyClamp(
+                  value, 0, (space.channels[0] as LinearChannel).max))
               : channels[0],
           clampChannel12
               ? channels[1].andThen((value) => fuzzyClamp(value, 0, 100))

lib/src/value/color/channel.dart

@@ -21,9 +21,21 @@ class ColorChannel {
   /// This is true if and only if this is not a [LinearChannel].
   final bool isPolarAngle;
 
+  /// The unit that's associated with this channel.
+  ///
+  /// Some channels are typically written without units, while others have a
+  /// specific unit that is conventionally applied to their values. Although any
+  /// compatible unit or unitless value will work for input¹, this unit is used
+  /// when the value is serialized or returned from a Sass function.
+  ///
+  /// 1: Unless [LinearChannel.requiresPercent] is set, in which case unitless
+  /// values are not allowed.
+  final String? associatedUnit;
+
   /// @nodoc
   @internal
-  const ColorChannel(this.name, {required this.isPolarAngle});
+  const ColorChannel(this.name,
+      {required this.isPolarAngle, this.associatedUnit});
 
   /// Returns whether this channel is [analogous] to [other].
   ///
@@ -65,9 +77,19 @@ class LinearChannel extends ColorChannel {
   /// forbids unitless values.
   final bool requiresPercent;
 
+  /// Creates a linear color channel.
+  ///
+  /// By default, [ColorChannel.associatedUnit] is set to `%` if and only if
+  /// [min] is 0 and [max] is 100. However, if [conventionallyPercent] is
+  /// true, it's set to `%`, and if it's false, it's set to null.
+  ///
   /// @nodoc
   @internal
   const LinearChannel(String name, this.min, this.max,
-      {this.requiresPercent = false})
-      : super(name, isPolarAngle: false);
+      {this.requiresPercent = false, bool? conventionallyPercent})
+      : super(name,
+            isPolarAngle: false,
+            associatedUnit: (conventionallyPercent ?? (min == 0 && max == 100))
+                ? '%'
+                : null);
 }

lib/src/value/color/space/oklab.dart

@@ -23,7 +23,7 @@ class OklabColorSpace extends ColorSpace {
 
   const OklabColorSpace()
       : super('oklab', const [
-          LinearChannel('lightness', 0, 1),
+          LinearChannel('lightness', 0, 1, conventionallyPercent: true),
           LinearChannel('a', -0.4, 0.4),
           LinearChannel('b', -0.4, 0.4)
         ]);

lib/src/value/color/space/oklch.dart

@@ -23,7 +23,7 @@ class OklchColorSpace extends ColorSpace {
 
   const OklchColorSpace()
       : super('oklch', const [
-          LinearChannel('lightness', 0, 1),
+          LinearChannel('lightness', 0, 1, conventionallyPercent: true),
           LinearChannel('chroma', 0, 0.4),
           hueChannel
         ]);

lib/src/value/color/space/utils.dart

@@ -14,7 +14,8 @@ const labKappa = 24389 / 27; // 29^3/3^3;
 const labEpsilon = 216 / 24389; // 6^3/29^3;
 
 /// The hue channel shared across all polar color spaces.
-const hueChannel = ColorChannel('hue', isPolarAngle: true);
+const hueChannel =
+    ColorChannel('hue', isPolarAngle: true, associatedUnit: 'deg');
 
 /// The color channels shared across all RGB color spaces (except the legacy RGB space).
 const rgbChannels = [

lib/src/visitor/serialize.dart

@@ -560,38 +560,29 @@ final class _SerializeVisitor
       case ColorSpace.rgb || ColorSpace.hsl || ColorSpace.hwb:
         _writeLegacyColor(value);
 
-      case ColorSpace.lab || ColorSpace.oklab:
+      case ColorSpace.lab ||
+            ColorSpace.oklab ||
+            ColorSpace.lch ||
+            ColorSpace.oklch:
         _buffer
           ..write(value.space)
           ..writeCharCode($lparen);
-        _writeChannel(value.channel0OrNull);
-        if (!_isCompressed &&
-            value.space == ColorSpace.lab &&
-            !value.isChannel0Missing) {
+        if (!_isCompressed && !value.isChannel0Missing) {
+          var max = (value.space.channels[0] as LinearChannel).max;
+          _writeNumber(value.channel0 * 100 / max);
           _buffer.writeCharCode($percent);
+        } else {
+          _writeChannel(value.channel0OrNull);
         }
         _buffer.writeCharCode($space);
         _writeChannel(value.channel1OrNull);
         _buffer.writeCharCode($space);
         _writeChannel(value.channel2OrNull);
-        _maybeWriteSlashAlpha(value);
-        _buffer.writeCharCode($rparen);
-
-      case ColorSpace.lch || ColorSpace.oklch:
-        _buffer
-          ..write(value.space)
-          ..writeCharCode($lparen);
-        _writeChannel(value.channel0OrNull);
         if (!_isCompressed &&
-            value.space == ColorSpace.lch &&
-            !value.isChannel0Missing) {
-          _buffer.writeCharCode($percent);
+            !value.isChannel2Missing &&
+            value.space.channels[2].isPolarAngle) {
+          _buffer.write('deg');
         }
-        _buffer.writeCharCode($space);
-        _writeChannel(value.channel1OrNull);
-        _buffer.writeCharCode($space);
-        _writeChannel(value.channel2OrNull);
-        if (!_isCompressed && !value.isChannel2Missing) _buffer.write('deg');
         _maybeWriteSlashAlpha(value);
         _buffer.writeCharCode($rparen);