webpack/lib/optimize/SideEffectsFlagPlugin.js

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

const HarmonyExportImportedSpecifierDependency = require("../dependencies/HarmonyExportImportedSpecifierDependency");
const HarmonyImportSideEffectDependency = require("../dependencies/HarmonyImportSideEffectDependency");
const HarmonyImportSpecifierDependency = require("../dependencies/HarmonyImportSpecifierDependency");

class SideEffectsFlagPlugin {

	apply(compiler) {
		compiler.hooks.normalModuleFactory.tap("SideEffectsFlagPlugin", (nmf) => {
			nmf.plugin("module", (module, data) => {
				const resolveData = data.resourceResolveData;
				if(resolveData && resolveData.descriptionFileData && resolveData.relativePath) {
					const sideEffects = resolveData.descriptionFileData.sideEffects;
					const isSideEffectFree = sideEffects === false; // TODO allow more complex expressions
					if(isSideEffectFree) {
						module.sideEffectFree = true;
					}
				}

				return module;
			});
		});
		compiler.hooks.compilation.tap("SideEffectsFlagPlugin", (compilation) => {
			compilation.hooks.optimizeDependencies.tap("SideEffectsFlagPlugin", (modules) => {
				const reexportMaps = new Map();

				// Capture reexports of sideEffectFree modules
				for(const module of modules) {
					const removeDependencies = [];
					for(const dep of module.dependencies) {
						if(dep instanceof HarmonyImportSideEffectDependency) {
							if(dep.module && dep.module.sideEffectFree) {
								removeDependencies.push(dep);
							}
						} else if(dep instanceof HarmonyExportImportedSpecifierDependency) {
							if(module.sideEffectFree) {
								const mode = dep.getMode(true);
								if(mode.type === "safe-reexport") {
									let map = reexportMaps.get(module);
									if(!map) {
										reexportMaps.set(module, map = new Map());
									}
									for(const pair of mode.map) {
										map.set(pair[0], {
											module: mode.module,
											exportName: pair[1]
										});
									}
								}
							}
						}
					}
					for(const dep of removeDependencies) {
						module.removeDependency(dep);
						dep.module.reasons = dep.module.reasons.filter(r => r.dependency !== dep);
					}
				}

				// Flatten reexports
				for(const map of reexportMaps.values()) {
					for(const pair of map) {
						let mapping = pair[1];
						while(mapping) {
							const innerMap = reexportMaps.get(mapping.module);
							if(!innerMap) break;
							const newMapping = innerMap.get(mapping.exportName);
							if(newMapping) {
								map.set(pair[0], newMapping);
							}
							mapping = newMapping;
						}
					}
				}

				// Update imports along the reexports from sideEffectFree modules
				const updates = [];
				for(const pair of reexportMaps) {
					const module = pair[0];
					const map = pair[1];
					for(const reason of module.reasons) {
						const dep = reason.dependency;
						if(dep instanceof HarmonyImportSpecifierDependency) {
							const mapping = map.get(dep.id);
							if(mapping) {
								updates.push({
									dep,
									mapping,
									module,
									reason
								});
							}
						}
					}
				}

				// Execute updates
				for(const update of updates) {
					const dep = update.dep;
					const mapping = update.mapping;
					const module = update.module;
					const reason = update.reason;
					dep.module = mapping.module;
					dep.id = mapping.exportName;
					module.removeReason(reason.module, dep);
					mapping.module.addReason(reason.module, dep);
				}
			});
		});
	}
}
module.exports = SideEffectsFlagPlugin;