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Closure Compiler is a JavaScript optimizing compiler. It parses your
JavaScript, analyzes it, removes dead code and rewrites and minimizes
what's left. It also checks syntax, variable references, and types, and
warns about common JavaScript pitfalls. It is used in many of Google's
JavaScript apps, including Gmail, Google Web Search, Google Maps, and
Google Docs.
/*
* Copyright 2018 The Closure Compiler Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.javascript.jscomp;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.annotations.VisibleForTesting;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.deps.ModuleLoader.ModulePath;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import javax.annotation.Nullable;
/**
* Rewrites an ES6 module to a CommonJS-like module for the sake of per-file transpilation +
* bunlding (e.g. Closure Bundler). Output is not meant to be type checked.
*/
public class Es6RewriteModulesToCommonJsModules implements CompilerPass {
private static final String JSCOMP_DEFAULT_EXPORT = "$$default";
private static final String MODULE = "$$module";
private static final String EXPORTS = "$$exports";
private static final String REQUIRE = "$$require";
private final AbstractCompiler compiler;
private final String pragma;
public Es6RewriteModulesToCommonJsModules(AbstractCompiler compiler) {
this(compiler, "use strict");
}
@VisibleForTesting
Es6RewriteModulesToCommonJsModules(AbstractCompiler compiler, String pragma) {
this.compiler = compiler;
this.pragma = pragma;
}
@Override
public void process(Node externs, Node root) {
for (Node script : root.children()) {
if (Es6RewriteModules.isEs6ModuleRoot(script)) {
NodeTraversal.traverseEs6(compiler, script, new Rewriter(compiler, script));
}
}
}
private static class LocalQName {
final String qName;
/**
* Node to use for source information. All exported properties are transpiled to ES5 getters so
* debuggers will automatically step into these, even with source maps. When stepping in this
* node will be displayed in the source map. In general it should either be the export itself
* (e.g. export function or class) or the specific name being exported (export specs, const,
* etc).
*/
final Node nodeForSourceInfo;
LocalQName(String qName, Node nodeForSourceInfo) {
this.qName = qName;
this.nodeForSourceInfo = nodeForSourceInfo;
}
}
/**
* Rewrites a single ES6 module into a CommonJS like module designed to be loaded in the
* compiler's module runtime.
*/
private class Rewriter extends AbstractPostOrderCallback {
private Node requireInsertSpot;
private final Node script;
private final Map exportedNameToLocalQName;
private final Set imports;
private final Set importRequests;
private final AbstractCompiler compiler;
private final ModulePath modulePath;
Rewriter(AbstractCompiler compiler, Node script) {
this.compiler = compiler;
this.script = script;
requireInsertSpot = null;
// TreeMap because ES6 orders the export key using natural ordering.
exportedNameToLocalQName = new TreeMap<>();
importRequests = new LinkedHashSet<>();
imports = new HashSet<>();
modulePath = compiler.getInput(script.getInputId()).getPath();
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
switch (n.getToken()) {
case IMPORT:
visitImport(n);
break;
case EXPORT:
visitExport(t, n, parent);
break;
case SCRIPT:
visitScript(t, n);
break;
case NAME:
maybeRenameImportedValue(t, n);
break;
default:
break;
}
}
/**
* Given an import node gets the name of the var to use for the imported module.
*
* Example:
* import {v} from './foo.js'; use(v);
* Can become:
* const module$foo = require('./foo.js'); use(module$foo.v);
* This method would return "module$foo".
*/
private String getVarNameOfImport(Node importDecl) {
checkState(importDecl.isImport());
return getVarNameOfImport(importDecl.getLastChild().getString());
}
private String getVarNameOfImport(String importRequest) {
return modulePath.resolveModuleAsPath(importRequest).toModuleName();
}
/**
* @return qualified name to use to reference an imported value.
* Examples:
*
* - If referencing an import spec like v in "import {v} from './foo.js'" then this
* would return "module$foo.v".
*
- If referencing an import star like m in "import * as m from './foo.js'" then this
* would return "module$foo".
*
- If referencing an import default like d in "import d from './foo.js'" then this
* would return "module$foo.default".
*
* Used to rename references to imported values within this module.
*/
private String getNameOfImportedValue(Node nameNode) {
Node importDecl = nameNode;
while (!importDecl.isImport()) {
importDecl = importDecl.getParent();
}
String moduleName = getVarNameOfImport(importDecl);
if (nameNode.getParent().isImportSpec()) {
return moduleName + "." + nameNode.getParent().getFirstChild().getString();
} else if (nameNode.isImportStar()) {
return moduleName;
} else {
checkState(nameNode.getParent().isImport());
return moduleName + ".default";
}
}
/**
* @param nameNode any variable name that is potentially from an import statement
* @return qualified name to use to reference an imported value if the given node is an imported
* name or null if the value is not imported or if it is in the import statement itself
*/
@Nullable
private String maybeGetNameOfImportedValue(Scope s, Node nameNode) {
checkState(nameNode.isName());
Var var = s.getVar(nameNode.getString());
if (var != null
// variables added implicitly to the scope, like arguments, have a null name node
&& var.getNameNode() != null
&& NodeUtil.isImportedName(var.getNameNode())
&& nameNode != var.getNameNode()) {
return getNameOfImportedValue(var.getNameNode());
}
return null;
}
/**
* Renames the given name node if it is an imported value.
*/
private void maybeRenameImportedValue(NodeTraversal t, Node n) {
checkState(n.isName());
Node parent = n.getParent();
if (parent.isExport()
|| parent.isExportSpec()
|| parent.isImport()
|| parent.isImportSpec()) {
return;
}
String qName = maybeGetNameOfImportedValue(t.getScope(), n);
if (qName != null) {
n.replaceWith(NodeUtil.newQName(compiler, qName));
t.reportCodeChange();
}
}
private void visitScript(NodeTraversal t, Node script) {
checkState(this.script == script);
Node moduleNode = script.getFirstChild();
checkState(moduleNode.isModuleBody());
moduleNode.detach();
script.addChildrenToFront(moduleNode.removeChildren());
// Order here is important. We want the end result to be:
// $jscomp.registerAndLoadModule(function($$require, $$exports, $$module) {
// // First to ensure circular deps can see exports of this module before we require them,
// // and also so that temporal deadzone is respected.
// //
// // Second so the module definition can reference imported modules, and so any require'd
// // modules are loaded.
// //
// // And finally last is the actual module definition.
// //
// }, /* */, [/* */]);
// As a result the calls below are in *inverse* order to what we want above so they can keep
// adding to the front of the script.
addRequireCalls();
addExportDef();
registerAndLoadModule(t);
}
/** Adds one call to require per imported module. */
private void addRequireCalls() {
if (!importRequests.isEmpty()) {
for (Node importDecl : imports) {
importDecl.detach();
}
Set importedNames = new HashSet<>();
for (String request : importRequests) {
String varName = getVarNameOfImport(request);
if (importedNames.add(varName)) {
Node requireCall = IR.call(IR.name(REQUIRE), IR.string(request));
requireCall.putBooleanProp(Node.FREE_CALL, true);
Node var = IR.var(IR.name(varName), requireCall);
var.useSourceInfoIfMissingFromForTree(script);
script.addChildAfter(var, requireInsertSpot);
requireInsertSpot = var;
}
}
}
}
/**
* Wraps the entire current module definition in a $jscomp.registerAndLoadModule function.
*/
private void registerAndLoadModule(NodeTraversal t) {
Node block = IR.block();
block.addChildrenToFront(script.removeChildren());
block.addChildToFront(IR.exprResult(IR.string(pragma)));
Node moduleFunction =
IR.function(
IR.name(""),
IR.paramList(IR.name(REQUIRE), IR.name(EXPORTS), IR.name(MODULE)),
block);
Node shallowDeps = new Node(Token.ARRAYLIT);
for (String request : importRequests) {
shallowDeps.addChildToBack(IR.string(request));
}
Node exprResult =
IR.exprResult(
IR.call(
IR.getprop(IR.name("$jscomp"), IR.string("registerAndLoadModule")),
moduleFunction,
// Specifically use the input's name rather than modulePath.toString(). The former
// is the raw path and the latter is encoded (special characters are replaced).
// This is designed to run in a web browser and we want to preserve the URL given
// to us. But the encodings will replace : with - due to windows.
IR.string(t.getInput().getName()),
shallowDeps));
script.addChildToBack(exprResult.useSourceInfoIfMissingFromForTree(script));
compiler.reportChangeToChangeScope(script);
compiler.reportChangeToChangeScope(moduleFunction);
t.reportCodeChange();
}
/** Adds exports to the exports object using Object.defineProperties. */
private void addExportDef() {
if (!exportedNameToLocalQName.isEmpty()) {
Node definePropertiesLit = IR.objectlit();
for (Map.Entry entry : exportedNameToLocalQName.entrySet()) {
addExport(definePropertiesLit, entry.getKey(), entry.getValue());
}
script.addChildToFront(
IR.exprResult(
IR.call(
NodeUtil.newQName(compiler, "Object.defineProperties"),
IR.name(EXPORTS),
definePropertiesLit))
.useSourceInfoIfMissingFromForTree(script));
}
}
/** Adds an ES5 getter to the given object literal to use an an export. */
private void addExport(Node definePropertiesLit, String exportedName, LocalQName localQName) {
Node exportedValue = NodeUtil.newQName(compiler, localQName.qName);
Node getterFunction =
IR.function(IR.name(""), IR.paramList(), IR.block(IR.returnNode(exportedValue)));
getterFunction.useSourceInfoFromForTree(localQName.nodeForSourceInfo);
Node objLit =
IR.objectlit(
IR.stringKey("enumerable", IR.trueNode()), IR.stringKey("get", getterFunction));
definePropertiesLit.addChildToBack(IR.stringKey(exportedName, objLit));
compiler.reportChangeToChangeScope(getterFunction);
}
private void visitImport(Node importDecl) {
importRequests.add(importDecl.getLastChild().getString());
imports.add(importDecl);
}
private void visitExportDefault(NodeTraversal t, Node export, Node parent) {
Node child = export.getFirstChild();
String name = null;
if (child.isFunction() || child.isClass()) {
name = NodeUtil.getName(child);
}
if (name != null) {
Node decl = child.detach();
parent.replaceChild(export, decl);
} else {
name = JSCOMP_DEFAULT_EXPORT;
// Default exports are constant in more ways than one. Not only can they not be
// overwritten but they also act like a const for temporal dead-zone purposes.
Node var = IR.constNode(IR.name(name), export.removeFirstChild());
parent.replaceChild(export, var.useSourceInfoIfMissingFromForTree(export));
}
exportedNameToLocalQName.put("default", new LocalQName(name, export));
t.reportCodeChange();
}
private void visitExportFrom(NodeTraversal t, Node export, Node parent) {
// export {x, y as z} from 'moduleIdentifier';
Node moduleIdentifier = export.getLastChild();
Node importNode = IR.importNode(IR.empty(), IR.empty(), moduleIdentifier.cloneNode());
importNode.useSourceInfoFrom(export);
parent.addChildBefore(importNode, export);
visit(t, importNode, parent);
String moduleName = getVarNameOfImport(moduleIdentifier.getString());
for (Node exportSpec : export.getFirstChild().children()) {
exportedNameToLocalQName.put(
exportSpec.getLastChild().getString(),
new LocalQName(moduleName + "." + exportSpec.getFirstChild().getString(), exportSpec));
}
parent.removeChild(export);
t.reportCodeChange();
}
private void visitExportSpecs(NodeTraversal t, Node export, Node parent) {
// export {Foo};
for (Node exportSpec : export.getFirstChild().children()) {
String localName = exportSpec.getFirstChild().getString();
Var var = t.getScope().getVar(localName);
if (var != null && NodeUtil.isImportedName(var.getNameNode())) {
localName = maybeGetNameOfImportedValue(t.getScope(), exportSpec.getFirstChild());
checkNotNull(localName);
}
exportedNameToLocalQName.put(
exportSpec.getLastChild().getString(), new LocalQName(localName, exportSpec));
}
parent.removeChild(export);
t.reportCodeChange();
}
private void visitExportNameDeclaration(Node declaration) {
// export var Foo;
// export let {a, b:[c,d]} = {};
List lhsNodes = NodeUtil.findLhsNodesInNode(declaration);
for (Node lhs : lhsNodes) {
checkState(lhs.isName());
String name = lhs.getString();
exportedNameToLocalQName.put(name, new LocalQName(name, lhs));
}
}
private void visitExportDeclaration(NodeTraversal t, Node export, Node parent) {
// export var Foo;
// export function Foo() {}
// etc.
Node declaration = export.getFirstChild();
if (NodeUtil.isNameDeclaration(declaration)) {
visitExportNameDeclaration(declaration);
} else {
checkState(declaration.isFunction() || declaration.isClass());
String name = declaration.getFirstChild().getString();
exportedNameToLocalQName.put(name, new LocalQName(name, export));
}
parent.replaceChild(export, declaration.detach());
t.reportCodeChange();
}
private void visitExport(NodeTraversal t, Node export, Node parent) {
if (export.getBooleanProp(Node.EXPORT_DEFAULT)) {
visitExportDefault(t, export, parent);
} else if (export.getBooleanProp(Node.EXPORT_ALL_FROM)) {
// TODO(johnplaisted)
compiler.report(JSError.make(export, Es6ToEs3Util.CANNOT_CONVERT_YET, "Wildcard export"));
} else if (export.hasTwoChildren()) {
visitExportFrom(t, export, parent);
} else {
if (export.getFirstChild().getToken() == Token.EXPORT_SPECS) {
visitExportSpecs(t, export, parent);
} else {
visitExportDeclaration(t, export, parent);
}
}
}
}
}