112 lines
3.8 KiB
JavaScript
112 lines
3.8 KiB
JavaScript
/*
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Copyright 2021 The Matrix.org Foundation C.I.C.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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const valueParser = require("postcss-value-parser");
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let aliasMap;
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let resolvedMap;
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let baseVariables;
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function getValueFromAlias(alias) {
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const derivedVariable = aliasMap.get(`--${alias}`);
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return baseVariables.get(derivedVariable) ?? resolvedMap.get(derivedVariable);
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}
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function parseDeclarationValue(value) {
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const parsed = valueParser(value);
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const variables = [];
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parsed.walk(node => {
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if (node.type !== "function" && node.value !== "var") {
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return;
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}
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const variable = node.nodes[0];
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variables.push(variable.value);
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});
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return variables;
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}
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function resolveDerivedVariable(decl, derive) {
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const RE_VARIABLE_VALUE = /--(.+)--(.+)-(.+)/;
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const variableCollection = parseDeclarationValue(decl.value);
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for (const variable of variableCollection) {
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const matches = variable.match(RE_VARIABLE_VALUE);
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if (matches) {
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const [wholeVariable, baseVariable, operation, argument] = matches;
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const value = baseVariables.get(`--${baseVariable}`) ?? getValueFromAlias(baseVariable);
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if (!value) {
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throw new Error(`Cannot derive from ${baseVariable} because it is neither defined in config nor is it an alias!`);
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}
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const derivedValue = derive(value, operation, argument);
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resolvedMap.set(wholeVariable, derivedValue);
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}
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}
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}
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function extract(decl) {
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if (decl.variable) {
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// see if right side is of form "var(--foo)"
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const wholeVariable = decl.value.match(/var\((--.+)\)/)?.[1];
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if (wholeVariable) {
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aliasMap.set(decl.prop, wholeVariable);
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// Since this is an alias, we shouldn't store it in baseVariables
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return;
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}
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baseVariables.set(decl.prop, decl.value);
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}
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}
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function addResolvedVariablesToRootSelector(root, {Rule, Declaration}) {
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const newRule = new Rule({ selector: ":root", source: root.source });
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// Add derived css variables to :root
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resolvedMap.forEach((value, key) => {
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const declaration = new Declaration({prop: key, value});
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newRule.append(declaration);
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});
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root.append(newRule);
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}
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/**
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* @callback derive
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* @param {string} value - The base value on which an operation is applied
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* @param {string} operation - The operation to be applied (eg: darker, lighter...)
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* @param {string} argument - The argument for this operation
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*/
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/**
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*
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* @param {Object} opts - Options for the plugin
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* @param {derive} opts.derive - The callback which contains the logic for resolving derived variables
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*/
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module.exports = (opts = {}) => {
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aliasMap = new Map();
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resolvedMap = new Map();
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baseVariables = new Map();
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return {
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postcssPlugin: "postcss-compile-variables",
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Once(root, {Rule, Declaration}) {
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/*
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Go through the CSS file once to extract all aliases and base variables.
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We use these when resolving derived variables later.
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*/
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root.walkDecls(decl => extract(decl));
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root.walkDecls(decl => resolveDerivedVariable(decl, opts.derive));
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addResolvedVariablesToRootSelector(root, {Rule, Declaration});
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},
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};
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};
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module.exports.postcss = true;
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