Add support for <contrast-color()>

It should serialize as defined in w3c/csswg-drafts#10328, ie. with preserved channel values.

Author: cdoublev

__tests__/value.js

@@ -3285,6 +3285,11 @@ describe('<color>', () => {
         ]
         valid.forEach(([input, expected = input]) => expect(parse('<color>', input)).toBe(expected))
     })
+    test('valid <contrast-color()>', () => {
+        // Preserve channel values except <hue> and <alpha-value>
+        expect(parse('<color>', 'contrast-color(rgba(-100% 200% 0 / 101%))')).toBe('contrast-color(rgb(-255 510 0))')
+        expect(parse('<color>', 'contrast-color(hsla(540deg -1% 0 / 50%))')).toBe('contrast-color(hsl(180 -1 0 / 0.5))')
+    })
 })
 describe('<combinator>', () => {
     test('invalid', () => {

lib/serialize.js

@@ -287,11 +287,11 @@ function serializeCalculationFunction({ range = {}, round, value }, forComputedO
 
 /**
  * @param {object} color
- * @param {boolean} mixed
+ * @param {boolean} specified
  * @returns {string}
  * @see {@link https://drafts.csswg.org/css-color-4/#serializing-color-values}
  */
-function serializeColor({ name, types, value }, mixed = false) {
+function serializeColor({ name, types, value }, specified = false) {
     if (types.includes('<keyword>')) {
         return value
     }
@@ -337,6 +337,15 @@ function serializeColor({ name, types, value }, mixed = false) {
     if (types.includes('<legacy-device-cmyk-syntax>')) {
         return `device-cmyk(${serializeCSSComponentValueList(value, ' ')})`
     }
+    if (types.includes('<contrast-color()>')) {
+        const [color, max] = value
+        let string = `contrast-color(${serializeColor(color, true)}`
+        if (!isOmitted(max)) {
+            string += ' max'
+        }
+        string += ')'
+        return string
+    }
     let alpha
     if (types.includes('<hex-color>')) {
         const [n1, n2, n3, n4, n5, n6, n7, n8] = value
@@ -451,7 +460,7 @@ function serializeColor({ name, types, value }, mixed = false) {
                     break
             }
         }
-        if (source || mixed) {
+        if (source || specified) {
             channels.push(value)
             return channels
         }
@@ -491,7 +500,7 @@ function serializeColor({ name, types, value }, mixed = false) {
         return channels
     }, [])
 
-    if (!resolved || source || mixed) {
+    if (!resolved || source || specified) {
         if (name === 'rgba' || name === 'hsla') {
             name = name.slice(0, -1)
         }