webpack/lib/dependencies/HarmonyDetectionParserPlugin.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const EnvironmentNotSupportAsyncWarning = require("../EnvironmentNotSupportAsyncWarning");
const { JAVASCRIPT_MODULE_TYPE_ESM } = require("../ModuleTypeConstants");
const DynamicExports = require("./DynamicExports");
const HarmonyCompatibilityDependency = require("./HarmonyCompatibilityDependency");
const HarmonyExports = require("./HarmonyExports");

/** @typedef {import("../Module").BuildMeta} BuildMeta */
/** @typedef {import("../javascript/JavascriptParser")} JavascriptParser */

const PLUGIN_NAME = "HarmonyDetectionParserPlugin";

module.exports = class HarmonyDetectionParserPlugin {
	/**
	 * Applies the plugin by registering its hooks on the compiler.
	 * @param {JavascriptParser} parser the parser
	 * @returns {void}
	 */
	apply(parser) {
		parser.hooks.program.tap(PLUGIN_NAME, (ast) => {
			const isStrictHarmony =
				parser.state.module.type === JAVASCRIPT_MODULE_TYPE_ESM;
			const isHarmony =
				isStrictHarmony ||
				ast.body.some(
					(statement) =>
						statement.type === "ImportDeclaration" ||
						statement.type === "ExportDefaultDeclaration" ||
						statement.type === "ExportNamedDeclaration" ||
						statement.type === "ExportAllDeclaration"
				);
			if (isHarmony) {
				const module = parser.state.module;
				const compatDep = new HarmonyCompatibilityDependency();
				compatDep.loc = {
					start: {
						line: -1,
						column: 0
					},
					end: {
						line: -1,
						column: 0
					},
					index: -3
				};
				module.addPresentationalDependency(compatDep);
				DynamicExports.bailout(parser.state);
				HarmonyExports.enable(parser.state, isStrictHarmony);
				parser.scope.isStrict = true;
			}
		});

		parser.hooks.topLevelAwait.tap(PLUGIN_NAME, () => {
			const module = parser.state.module;
			if (!HarmonyExports.isEnabled(parser.state)) {
				throw new Error(
					"Top-level-await is only supported in EcmaScript Modules"
				);
			}
			/** @type {BuildMeta} */
			(module.buildMeta).async = true;
			EnvironmentNotSupportAsyncWarning.check(
				module,
				parser.state.compilation.runtimeTemplate,
				"topLevelAwait"
			);
		});

		/**
		 * Returns true if in harmony.
		 * @returns {boolean | undefined} true if in harmony
		 */
		const skipInHarmony = () => {
			if (HarmonyExports.isEnabled(parser.state)) {
				return true;
			}
		};

		/**
		 * Returns null if in harmony.
		 * @returns {null | undefined} null if in harmony
		 */
		const nullInHarmony = () => {
			if (HarmonyExports.isEnabled(parser.state)) {
				return null;
			}
		};

		const nonHarmonyIdentifiers = ["define", "exports"];
		for (const identifier of nonHarmonyIdentifiers) {
			parser.hooks.evaluateTypeof
				.for(identifier)
				.tap(PLUGIN_NAME, nullInHarmony);
			parser.hooks.typeof.for(identifier).tap(PLUGIN_NAME, skipInHarmony);
			parser.hooks.evaluate.for(identifier).tap(PLUGIN_NAME, nullInHarmony);
			parser.hooks.expression.for(identifier).tap(PLUGIN_NAME, skipInHarmony);
			parser.hooks.call.for(identifier).tap(PLUGIN_NAME, skipInHarmony);
		}
	}
};