less/lib/less/transform-tree.js

Leaner CSS

import contexts from './contexts.js';
import visitor from './visitors/index.js';
import tree from './tree/index.js';

/**
 * @param {import('./tree/node.js').default} root
 * @param {{ variables?: Record<string, *>, compress?: boolean, pluginManager?: *, frames?: *[] }} options
 * @returns {import('./tree/node.js').default}
 */
export default function(root, options) {
    options = options || {};
    let evaldRoot;
    let variables = options.variables;
    const evalEnv = new contexts.Eval(options);

    //
    // Allows setting variables with a hash, so:
    //
    //   `{ color: new tree.Color('#f01') }` will become:
    //
    //   new tree.Declaration('@color',
    //     new tree.Value([
    //       new tree.Expression([
    //         new tree.Color('#f01')
    //       ])
    //     ])
    //   )
    //
    if (typeof variables === 'object' && !Array.isArray(variables)) {
        variables = Object.keys(variables).map(function (k) {
            let value = variables[k];

            if (!(value instanceof tree.Value)) {
                if (!(value instanceof tree.Expression)) {
                    value = new tree.Expression([value]);
                }
                value = new tree.Value([value]);
            }
            return new tree.Declaration(`@${k}`, value, false, null, 0);
        });
        evalEnv.frames = [new tree.Ruleset(null, variables)];
    }

    const visitors = [
        new visitor.JoinSelectorVisitor(),
        new visitor.MarkVisibleSelectorsVisitor(true),
        new visitor.ExtendVisitor(),
        new visitor.ToCSSVisitor({compress: Boolean(options.compress)})
    ];

    const preEvalVisitors = [];
    let v;
    let visitorIterator;

    /**
     * first() / get() allows visitors to be added while visiting
     * 
     * @todo Add scoping for visitors just like functions for @plugin; right now they're global
     */
    if (options.pluginManager) {
        visitorIterator = options.pluginManager.visitor();
        for (let i = 0; i < 2; i++) {
            visitorIterator.first();
            while ((v = visitorIterator.get())) {
                if (v.isPreEvalVisitor) {
                    if (i === 0 || preEvalVisitors.indexOf(v) === -1) {
                        preEvalVisitors.push(v);
                        v.run(root);
                    }
                }
                else {
                    if (i === 0 || visitors.indexOf(v) === -1) {
                        if (v.isPreVisitor) {
                            visitors.unshift(v);
                        }
                        else {
                            visitors.push(v);
                        }
                    }
                }
            }
        }
    }

    evaldRoot = root.eval(evalEnv);

    for (let i = 0; i < visitors.length; i++) {
        visitors[i].run(evaldRoot);
    }

    // Run any remaining visitors added after eval pass
    if (options.pluginManager) {
        visitorIterator.first();
        while ((v = visitorIterator.get())) {
            if (visitors.indexOf(v) === -1 && preEvalVisitors.indexOf(v) === -1) {
                v.run(evaldRoot);
            }
        }
    }

    return evaldRoot;
}