106 lines
3.7 KiB
JavaScript
106 lines
3.7 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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function getValueFromAlias(alias, variables) {
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const derivedVariable = aliasMap.get(`--${alias}`);
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return variables[derivedVariable] ?? resolvedMap.get(`--${derivedVariable}`); // what if we haven't resolved this variable yet?
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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, {variables, 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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if (!variables[baseVariable]) {
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// hmm.. baseVariable should be in config..., maybe this is an alias?
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if (!aliasMap.get(`--${baseVariable}`)) {
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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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}
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const value = variables[baseVariable] ?? getValueFromAlias(baseVariable, variables);
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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 extractAlias(decl) {
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const wholeVariable = decl.value.match(/var\(--(.+)\)/)?.[1];
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if (decl.prop.startsWith("--") && wholeVariable) {
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aliasMap.set(decl.prop, wholeVariable);
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}
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}
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function addResolvedVariablesToRootSelector(root, variables, { Rule, Declaration }) {
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const newRule = new Rule({ selector: ":root", source: root.source });
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// Add base css variables to :root
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for (const [key, value] of Object.entries(variables)) {
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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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// 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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* @type {import('postcss').PluginCreator}
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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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const {variables} = opts;
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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.
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We use the extracted alias when resolving derived variables
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later.
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*/
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root.walkDecls(decl => extractAlias(decl));
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root.walkDecls(decl => resolveDerivedVariable(decl, opts));
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addResolvedVariablesToRootSelector(root, variables, { 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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