Minor refactoring

The refactorized implementation was brittle because it depended on the relative
color syntax always being the top-level value definition of color functions,
which might not always be true.

The new implementation may slightly increase time complexity but significantly
decrease code complexity because it is the most idiomatic way to check that a
source color has been specified.

Author: cdoublev

lib/parse/replace.js

@@ -1,9 +1,9 @@
 
 const { colorFunctionKeywords, colorSpaces, colorSpaceKeywords } = require('../values/colors.js')
 const { getCalculationType, matchNumericType } = require('./types.js')
-const { isAmpersand, isOmitted } = require('../utils/value.js')
 const createError = require('../error.js')
 const { findSibling } = require('../utils/context.js')
+const { isAmpersand } = require('../utils/value.js')
 const { simplifyCalculation } = require('./simplify.js')
 const substitutions = require('../values/substitutions.js')
 
@@ -109,8 +109,7 @@ function resolveColorChannelDefinition(node) {
     const { context: { trees } } = node
     // Find the deepest tree whose context is a color function
     for (let index = trees.length; 0 < index; --index) {
-        const tree = trees[index - 1]
-        const { children, context: { replaced, function: fn } } = tree
+        const { [index - 1]: { context: { replaced, function: fn } }} = trees
         if (fn) {
             const { definition: { name } } = fn
             // Ignore trees of numeric substitution functions and their arguments
@@ -120,15 +119,13 @@ function resolveColorChannelDefinition(node) {
                 continue
             }
             // There must be a source color for color keywords to be valid
-            const source = children[0]
-            if (source?.definition.type !== 'optional' || isOmitted(source.value)) {
-                return null
-            }
-            if (name === 'color') {
-                const colorSpace = findSibling(node, node => colorSpaces.includes(node.definition.name))
-                return colorSpaceKeywords[colorSpace.definition.name]
+            if (findSibling(node, node => node.definition.name === '<color>')) {
+                if (name === 'color') {
+                    const colorSpace = findSibling(node, node => colorSpaces.includes(node.definition.name))
+                    return colorSpaceKeywords[colorSpace.definition.name]
+                }
+                return colorFunctionKeywords[name]
             }
-            return colorFunctionKeywords[name]
         }
         return null
     }