94 lines
2.9 KiB
Plaintext
94 lines
2.9 KiB
Plaintext
export default function collapseDuplicateDeclarations() {
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return (root) => {
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root.walkRules((node) => {
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let seen = new Map()
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let droppable = new Set([])
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let byProperty = new Map()
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node.walkDecls((decl) => {
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// This could happen if we have nested selectors. In that case the
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// parent will loop over all its declarations but also the declarations
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// of nested rules. With this we ensure that we are shallowly checking
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// declarations.
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if (decl.parent !== node) {
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return
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}
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if (seen.has(decl.prop)) {
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// Exact same value as what we have seen so far
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if (seen.get(decl.prop).value === decl.value) {
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// Keep the last one, drop the one we've seen so far
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droppable.add(seen.get(decl.prop))
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// Override the existing one with the new value. This is necessary
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// so that if we happen to have more than one declaration with the
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// same value, that we keep removing the previous one. Otherwise we
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// will only remove the *first* one.
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seen.set(decl.prop, decl)
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return
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}
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// Not the same value, so we need to check if we can merge it so
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// let's collect it first.
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if (!byProperty.has(decl.prop)) {
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byProperty.set(decl.prop, new Set())
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}
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byProperty.get(decl.prop).add(seen.get(decl.prop))
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byProperty.get(decl.prop).add(decl)
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}
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seen.set(decl.prop, decl)
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})
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// Drop all the duplicate declarations with the exact same value we've
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// already seen so far.
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for (let decl of droppable) {
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decl.remove()
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}
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// Analyze the declarations based on its unit, drop all the declarations
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// with the same unit but the last one in the list.
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for (let declarations of byProperty.values()) {
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let byUnit = new Map()
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for (let decl of declarations) {
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let unit = resolveUnit(decl.value)
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if (unit === null) {
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// We don't have a unit, so should never try and collapse this
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// value. This is because we can't know how to do it in a correct
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// way (e.g.: overrides for older browsers)
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continue
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}
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if (!byUnit.has(unit)) {
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byUnit.set(unit, new Set())
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}
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byUnit.get(unit).add(decl)
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}
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for (let declarations of byUnit.values()) {
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// Get all but the last one
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let removableDeclarations = Array.from(declarations).slice(0, -1)
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for (let decl of removableDeclarations) {
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decl.remove()
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}
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}
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}
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})
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}
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}
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let UNITLESS_NUMBER = Symbol('unitless-number')
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function resolveUnit(input) {
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let result = /^-?\d*.?\d+([\w%]+)?$/g.exec(input)
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if (result) {
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return result[1] ?? UNITLESS_NUMBER
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}
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return null
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}
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