polymer-build/lib/babel-plugin-import-meta.js

A library of Gulp build tasks

"use strict";
/**
 * @license
 * Copyright (c) 2018 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at
 * http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at
 * http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at
 * http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at
 * http://polymer.github.io/PATENTS.txt
 */
Object.defineProperty(exports, "__esModule", { value: true });
const plugin_syntax_import_meta_1 = require("@babel/plugin-syntax-import-meta");
const template_1 = require("@babel/template");
const ast = template_1.default.ast;
/**
 * Rewrites `import.meta`[1] into an import for a module named "meta". It is
 * expected this plugin runs alongside @babel/plugin-transform-modules-amd which
 * will transform this import into an AMD dependency, and is loaded using
 * @polymer/esm-amd-loader which will provide an object with a `url`[2] property
 * for the "meta" dependency.
 *
 * [1]: https://github.com/tc39/proposal-import-meta
 * [2]: https://html.spec.whatwg.org/#hostgetimportmetaproperties
 */
exports.rewriteImportMeta = {
    inherits: plugin_syntax_import_meta_1.default,
    visitor: {
        Program(path) {
            const metas = [];
            const identifiers = new Set();
            path.traverse({
                MetaProperty(path) {
                    const node = path.node;
                    if (node.meta && node.meta.name === 'import' &&
                        node.property.name === 'meta') {
                        metas.push(path);
                        for (const name of Object.keys(path.scope.getAllBindings())) {
                            identifiers.add(name);
                        }
                    }
                }
            });
            if (metas.length === 0) {
                return;
            }
            let metaId = 'meta';
            while (identifiers.has(metaId)) {
                metaId = path.scope.generateUidIdentifier('meta').name;
            }
            path.node.body.unshift(ast `import * as ${metaId} from 'meta';`);
            for (const meta of metas) {
                meta.replaceWith(ast `${metaId}`);
            }
        },
    }
};
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