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2 years ago
'use strict';
const OVERRIDABLE_RULES = new Set(['keyframes', 'counter-style']);
const SCOPE_RULES = new Set(['media', 'supports']);
/**
* @param {string} prop
* @return {string}
*/
function vendorUnprefixed(prop) {
return prop.replace(/^-\w+-/, '');
}
/**
* @param {string} name
* @return {boolean}
*/
function isOverridable(name) {
return OVERRIDABLE_RULES.has(vendorUnprefixed(name.toLowerCase()));
}
/**
* @param {string} name
* @return {boolean}
*/
function isScope(name) {
return SCOPE_RULES.has(vendorUnprefixed(name.toLowerCase()));
}
/**
* @param {import('postcss').AtRule} node
* @return {string}
*/
function getScope(node) {
/** @type {import('postcss').Container<import('postcss').ChildNode> | import('postcss').Document | undefined} */
let current = node.parent;
const chain = [node.name.toLowerCase(), node.params];
while (current) {
if (
current.type === 'atrule' &&
isScope(/** @type import('postcss').AtRule */ (current).name)
) {
chain.unshift(
/** @type import('postcss').AtRule */ (current).name +
' ' +
/** @type import('postcss').AtRule */ (current).params
);
}
current = current.parent;
}
return chain.join('|');
}
/**
* @type {import('postcss').PluginCreator<void>}
* @return {import('postcss').Plugin}
*/
function pluginCreator() {
return {
postcssPlugin: 'postcss-discard-overridden',
prepare() {
const cache = new Map();
/** @type {{node: import('postcss').AtRule, scope: string}[]} */
const rules = [];
return {
OnceExit(css) {
css.walkAtRules((node) => {
if (isOverridable(node.name)) {
const scope = getScope(node);
cache.set(scope, node);
rules.push({
node,
scope,
});
}
});
rules.forEach((rule) => {
if (cache.get(rule.scope) !== rule.node) {
rule.node.remove();
}
});
},
};
},
};
}
pluginCreator.postcss = true;
module.exports = pluginCreator;