webpack/lib/dependencies/HarmonyExportInitFragment.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 InitFragment = require("../InitFragment");
const RuntimeGlobals = require("../RuntimeGlobals");
const { first } = require("../util/SetHelpers");
const { propertyName } = require("../util/property");

/** @typedef {import("webpack-sources").Source} Source */
/** @typedef {import("../Generator").GenerateContext} GenerateContext */
/** @typedef {import("../ExportsInfo").UsedName} UsedName */

/**
 * Join iterable with comma.
 * @param {Iterable<string>} iterable iterable strings
 * @returns {string} result
 */
const joinIterableWithComma = (iterable) => {
	// This is more performant than Array.from().join(", ")
	// as it doesn't create an array
	let str = "";
	let first = true;
	for (const item of iterable) {
		if (first) {
			first = false;
		} else {
			str += ", ";
		}
		str += item;
	}
	return str;
};

/** @typedef {Map<UsedName, string>} ExportMap */
/** @typedef {Set<string>} UnusedExports */

/** @type {ExportMap} */
const EMPTY_MAP = new Map();
/** @type {UnusedExports} */
const EMPTY_SET = new Set();

/**
 * Represents HarmonyExportInitFragment.
 * @extends {InitFragment<GenerateContext>} Context
 */
class HarmonyExportInitFragment extends InitFragment {
	/**
	 * Creates an instance of HarmonyExportInitFragment.
	 * @param {string} exportsArgument the exports identifier
	 * @param {ExportMap} exportMap mapping from used name to exposed variable name
	 * @param {UnusedExports} unusedExports list of unused export names
	 */
	constructor(
		exportsArgument,
		exportMap = EMPTY_MAP,
		unusedExports = EMPTY_SET
	) {
		super(undefined, InitFragment.STAGE_HARMONY_EXPORTS, 1, "harmony-exports");
		/** @type {string} */
		this.exportsArgument = exportsArgument;
		/** @type {ExportMap} */
		this.exportMap = exportMap;
		/** @type {UnusedExports} */
		this.unusedExports = unusedExports;
	}

	/**
	 * Merges the provided values into a single result.
	 * @param {HarmonyExportInitFragment[]} fragments all fragments to merge
	 * @returns {HarmonyExportInitFragment} merged fragment
	 */
	mergeAll(fragments) {
		/** @type {undefined | ExportMap} */
		let exportMap;
		let exportMapOwned = false;
		/** @type {undefined | UnusedExports} */
		let unusedExports;
		let unusedExportsOwned = false;

		for (const fragment of fragments) {
			if (fragment.exportMap.size !== 0) {
				if (exportMap === undefined) {
					exportMap = fragment.exportMap;
					exportMapOwned = false;
				} else {
					if (!exportMapOwned) {
						exportMap = new Map(exportMap);
						exportMapOwned = true;
					}
					for (const [key, value] of fragment.exportMap) {
						if (!exportMap.has(key)) exportMap.set(key, value);
					}
				}
			}
			if (fragment.unusedExports.size !== 0) {
				if (unusedExports === undefined) {
					unusedExports = fragment.unusedExports;
					unusedExportsOwned = false;
				} else {
					if (!unusedExportsOwned) {
						unusedExports = new Set(unusedExports);
						unusedExportsOwned = true;
					}
					for (const value of fragment.unusedExports) {
						unusedExports.add(value);
					}
				}
			}
		}
		return new HarmonyExportInitFragment(
			this.exportsArgument,
			exportMap,
			unusedExports
		);
	}

	/**
	 * Returns merged result.
	 * @param {HarmonyExportInitFragment} other other
	 * @returns {HarmonyExportInitFragment} merged result
	 */
	merge(other) {
		/** @type {ExportMap} */
		let exportMap;
		if (this.exportMap.size === 0) {
			exportMap = other.exportMap;
		} else if (other.exportMap.size === 0) {
			exportMap = this.exportMap;
		} else {
			exportMap = new Map(other.exportMap);
			for (const [key, value] of this.exportMap) {
				if (!exportMap.has(key)) exportMap.set(key, value);
			}
		}
		/** @type {UnusedExports} */
		let unusedExports;
		if (this.unusedExports.size === 0) {
			unusedExports = other.unusedExports;
		} else if (other.unusedExports.size === 0) {
			unusedExports = this.unusedExports;
		} else {
			unusedExports = new Set(other.unusedExports);
			for (const value of this.unusedExports) {
				unusedExports.add(value);
			}
		}
		return new HarmonyExportInitFragment(
			this.exportsArgument,
			exportMap,
			unusedExports
		);
	}

	/**
	 * Returns the source code that will be included as initialization code.
	 * @param {GenerateContext} context context
	 * @returns {string | Source | undefined} the source code that will be included as initialization code
	 */
	getContent({ runtimeTemplate, runtimeRequirements }) {
		runtimeRequirements.add(RuntimeGlobals.exports);
		runtimeRequirements.add(RuntimeGlobals.definePropertyGetters);

		const unusedPart =
			this.unusedExports.size > 1
				? `/* unused harmony exports ${joinIterableWithComma(
						this.unusedExports
					)} */\n`
				: this.unusedExports.size > 0
					? `/* unused harmony export ${first(this.unusedExports)} */\n`
					: "";
		/** @type {string[]} */
		const definitions = [];
		const orderedExportMap = [...this.exportMap].sort(([a], [b]) =>
			a < b ? -1 : 1
		);
		for (const [key, value] of orderedExportMap) {
			definitions.push(
				`\n/* harmony export */   ${propertyName(
					/** @type {string} */ (key)
				)}: ${runtimeTemplate.returningFunction(value)}`
			);
		}
		const definePart =
			this.exportMap.size > 0
				? `/* harmony export */ ${RuntimeGlobals.definePropertyGetters}(${
						this.exportsArgument
					}, {${definitions.join(",")}\n/* harmony export */ });\n`
				: "";
		return `${definePart}${unusedPart}`;
	}
}

module.exports = HarmonyExportInitFragment;