com.google.javascript.jscomp.RewriteAsyncFunctions Maven / Gradle / Ivy
/*
* Copyright 2016 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.jstype.FunctionType;
import com.google.javascript.rhino.jstype.JSType;
import com.google.javascript.rhino.jstype.JSTypeRegistry;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;
import javax.annotation.Nullable;
/**
* Converts async functions to valid ES6 generator functions code.
*
* This pass must run before the passes that transpile let declarations, arrow functions, and
* generators.
*
*
An async function, foo(a, b), will be rewritten as:
*
*
{@code
* function foo(a, b) {
* let $jscomp$async$this = this;
* let $jscomp$async$arguments = arguments;
* let $jscomp$async$super$get$x = () => super.x;
* return $jscomp.asyncExecutePromiseGeneratorFunction(
* function* () {
* // original body of foo() with:
* // - await (x) replaced with yield (x)
* // - arguments replaced with $jscomp$async$arguments
* // - this replaced with $jscomp$async$this
* // - super.x replaced with $jscomp$async$super$get$x()
* // - super.x(5) replaced with $jscomp$async$super$get$x().call($jscomp$async$this, 5)
* });
* }}
*/
public final class RewriteAsyncFunctions implements NodeTraversal.Callback, HotSwapCompilerPass {
private static final String ASYNC_ARGUMENTS = "$jscomp$async$arguments";
private static final String ASYNC_THIS = "$jscomp$async$this";
private static final String ASYNC_SUPER_PROP_GETTER_PREFIX = "$jscomp$async$super$get$";
/**
* Information needed to replace a reference to `super.propertyName` with a call to a wrapper
* function.
*/
private final class SuperPropertyWrapperInfo {
// The first `super.property` Node we come across during traversal.
// Information from this node will be used when creating the wrapper function.
private final Node firstInstanceOfSuperDotProperty;
private final String wrapperFunctionName;
// The type to use for the wrapper function.
// Will be null if type checking has not run.
@Nullable private final JSType wrapperFunctionType;
private SuperPropertyWrapperInfo(
Node firstSuperDotPropertyNode, String wrapperFunctionName, JSType wrapperFunctionType) {
this.firstInstanceOfSuperDotProperty = firstSuperDotPropertyNode;
this.wrapperFunctionName = wrapperFunctionName;
this.wrapperFunctionType = wrapperFunctionType;
}
@Nullable
private JSType getPropertyType() {
return firstInstanceOfSuperDotProperty.getJSType();
}
private Node createWrapperFunctionNameNode() {
return astFactory.createName(wrapperFunctionName, wrapperFunctionType);
}
private Node createWrapperFunctionCallNode() {
return astFactory.createCall(createWrapperFunctionNameNode());
}
}
/**
* Used to collect information about properties referenced via `super.propertyName` within an
* async function.
*
* We'll have to replace these references with calls to a wrapper function.
*/
private final class SuperPropertyWrappers {
// Use LinkedHashMap in order to ensure the ordering is the same on every compile of the same
// source code.
// Note that the JSTypes will be null if type checking hasn't run.
private final Map propertyNameToTypeMap =
new LinkedHashMap<>();
private SuperPropertyWrapperInfo getOrCreateSuperPropertyWrapperInfo(
Node superDotPropertyNode) {
checkArgument(superDotPropertyNode.isGetProp(), superDotPropertyNode);
Node superNode = superDotPropertyNode.getFirstChild();
checkArgument(superNode.isSuper(), superNode);
Node propertyNameNode = superDotPropertyNode.getLastChild();
checkArgument(propertyNameNode.isString(), propertyNameNode);
String propertyName = propertyNameNode.getString();
JSType propertyType = superDotPropertyNode.getJSType();
final SuperPropertyWrapperInfo superPropertyWrapperInfo;
if (propertyNameToTypeMap.containsKey(propertyName)) {
superPropertyWrapperInfo = propertyNameToTypeMap.get(propertyName);
// Every reference to `super.propertyName` within a single lexical context should
// have the same type. Make sure this is true.
JSType existingJSType = superPropertyWrapperInfo.getPropertyType();
checkState(
Objects.equals(existingJSType, propertyType),
"Previous reference type: %s differs from current reference type: %s",
existingJSType,
propertyType);
} else {
superPropertyWrapperInfo = createNewInfo(superDotPropertyNode);
propertyNameToTypeMap.put(propertyName, superPropertyWrapperInfo);
}
return superPropertyWrapperInfo;
}
private SuperPropertyWrapperInfo createNewInfo(Node firstSuperDotPropertyNode) {
checkArgument(firstSuperDotPropertyNode.isGetProp(), firstSuperDotPropertyNode);
String propertyName = firstSuperDotPropertyNode.getLastChild().getString();
JSType propertyType = firstSuperDotPropertyNode.getJSType();
final String wrapperFunctionName = ASYNC_SUPER_PROP_GETTER_PREFIX + propertyName;
final JSType wrapperFunctionType;
if (propertyType == null) {
// type checking hasn't run, so we don't need type information.
wrapperFunctionType = null;
} else {
wrapperFunctionType = FunctionType.builder(registry).withReturnType(propertyType).build();
}
return new SuperPropertyWrapperInfo(
firstSuperDotPropertyNode, wrapperFunctionName, wrapperFunctionType);
}
private Collection asCollection() {
return propertyNameToTypeMap.values();
}
}
/**
* Keeps track of whether we're examining nodes within an async function & what changes are needed
* for the function currently in context.
*/
private final class LexicalContext {
@Nullable final Node function;
@Nullable final LexicalContext asyncThisAndArgumentsContext;
final SuperPropertyWrappers superPropertyWrappers = new SuperPropertyWrappers();
boolean mustAddAsyncThisVariable = false;
boolean mustAddAsyncArgumentsVariable = false;
LexicalContext() {
function = null;
asyncThisAndArgumentsContext = null;
}
LexicalContext(LexicalContext outer, Node function) {
this.function = checkNotNull(function);
if (function.isAsyncFunction()) {
if (function.isArrowFunction()) {
// An async arrow function context points to outer.asyncThisAndArgumentsContext
// if non-null, otherwise to itself.
asyncThisAndArgumentsContext = outer.asyncThisAndArgumentsContext == null
? this : outer.asyncThisAndArgumentsContext;
} else {
// An async non-arrow function context always points to itself
asyncThisAndArgumentsContext = this;
}
} else {
if (function.isArrowFunction()) {
// A non-async arrow function context always points to outer.asyncThisAndArgumentsContext
asyncThisAndArgumentsContext = outer.asyncThisAndArgumentsContext;
} else {
// A non-async, non-arrow function has no async context.
asyncThisAndArgumentsContext = null;
}
}
}
boolean isAsyncContext() {
return function.isAsyncFunction();
}
boolean mustReplaceThisAndArguments() {
return asyncThisAndArgumentsContext != null;
}
void recordAsyncThisReplacementWasDone() {
asyncThisAndArgumentsContext.mustAddAsyncThisVariable = true;
}
SuperPropertyWrapperInfo getOrCreateSuperPropertyWrapperInfo(Node superDotPropertyNode) {
return asyncThisAndArgumentsContext.superPropertyWrappers.getOrCreateSuperPropertyWrapperInfo(
superDotPropertyNode);
}
void recordAsyncArgumentsReplacementWasDone() {
asyncThisAndArgumentsContext.mustAddAsyncArgumentsVariable = true;
}
/**
* Creates a new reference to the variable used to hold the value of `this` for async functions.
*/
Node createThisVariableReference() {
recordAsyncThisReplacementWasDone();
return astFactory.createThisAliasReferenceForFunction(
ASYNC_THIS, asyncThisAndArgumentsContext.function);
}
/** Creates a correctly typed `this` node for this context. */
Node createThisReference() {
return astFactory.createThisForFunction(asyncThisAndArgumentsContext.function);
}
private Node createWrapperArrowFunction(SuperPropertyWrapperInfo wrapperInfo) {
// super.propertyName
final Node superDotProperty = wrapperInfo.firstInstanceOfSuperDotProperty.cloneTree();
if (rewriteSuperPropertyReferencesWithoutSuper) {
// Rewrite to avoid using `super` within an arrow function.
// See more information on definition of this option.
// TODO(bradfordcsmith): RewriteAsyncIteration and RewriteAsyncFunctions have the
// same logic for dealing with super references. Consider having them share
// it from a common place instead of duplicating.
final Node thisNode = createThisReference();
final Node prototypeOfThisNode = astFactory.createObjectGetPrototypeOfCall(thisNode);
final Node originalSuperNode = superDotProperty.getFirstChild();
// NOTE: must look at the enclosing MEMBER_FUNCTION_DEF to see if the method is static
if (asyncThisAndArgumentsContext.function.getParent().isStaticMember()) {
// For static methods `this` is the class and its direct prototype is the parent
// class and the super node we want
// super.propertyName -> Object.getPrototypeOf(this).propertyName
originalSuperNode.replaceWith(prototypeOfThisNode);
} else {
// For instance methods `this` is the instance, and its direct prototype is the
// ClassName.prototype object. We must go to the prototype of that to get the correct
// value for `super`.
// super.propertyName -> Object.getPrototypeOf(Object.getPrototypeOf(this)).propertyName
originalSuperNode.replaceWith(
astFactory.createObjectGetPrototypeOfCall(prototypeOfThisNode));
}
}
// () => super.propertyName
// OR avoid super for static method (class object -> superclass object)
// () => Object.getPrototypeOf(this).x
// OR avoid super for instance method (instance -> prototype -> super prototype)
// () => Object.getPrototypeOf(Object.getPrototypeOf(this)).x
return astFactory.createZeroArgArrowFunctionForExpression(superDotProperty);
}
}
private static final FeatureSet transpiledFeatures =
FeatureSet.BARE_MINIMUM.with(Feature.ASYNC_FUNCTIONS);
private final Deque contextStack;
private final AbstractCompiler compiler;
/**
* If this option is set to true, then this pass will rewrite references to properties using super
* (e.g. `super.method()`) to avoid using `super` within an arrow function.
*
* This option exists due to a bug in MS Edge 17 which causes it to fail to access super
* properties correctly from within arrow functions.
*
*
See https://github.com/Microsoft/ChakraCore/issues/5784
*
*
If the final compiler output will not include ES6 classes, this option should not be set. It
* isn't needed since the `super` references will be transpiled away anyway. Also, when this
* option is set it uses `Object.getPrototypeOf()` to rewrite `super`, which may not exist in
* pre-ES6 JS environments.
*/
private final boolean rewriteSuperPropertyReferencesWithoutSuper;
private final JSTypeRegistry registry;
private final AstFactory astFactory;
private RewriteAsyncFunctions(Builder builder) {
checkNotNull(builder);
this.compiler = builder.compiler;
this.contextStack = new ArrayDeque<>();
this.contextStack.addFirst(new LexicalContext());
this.rewriteSuperPropertyReferencesWithoutSuper =
builder.rewriteSuperPropertyReferencesWithoutSuper;
this.registry = checkNotNull(builder.registry);
this.astFactory = checkNotNull(builder.astFactory);
}
static class Builder {
private final AbstractCompiler compiler;
private boolean rewriteSuperPropertyReferencesWithoutSuper = false;
private JSTypeRegistry registry;
private AstFactory astFactory;
Builder(AbstractCompiler compiler) {
checkNotNull(compiler);
this.compiler = compiler;
}
Builder rewriteSuperPropertyReferencesWithoutSuper(boolean value) {
rewriteSuperPropertyReferencesWithoutSuper = value;
return this;
}
RewriteAsyncFunctions build() {
astFactory = compiler.createAstFactory();
registry = compiler.getTypeRegistry();
return new RewriteAsyncFunctions(this);
}
}
@Override
public void process(Node externs, Node root) {
TranspilationPasses.processTranspile(compiler, externs, transpiledFeatures, this);
TranspilationPasses.processTranspile(compiler, root, transpiledFeatures, this);
TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
}
@Override
public void hotSwapScript(Node scriptRoot, Node originalRoot) {
TranspilationPasses.hotSwapTranspile(compiler, scriptRoot, transpiledFeatures, this);
TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
}
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
if (n.isFunction()) {
contextStack.addFirst(new LexicalContext(contextStack.getFirst(), n));
}
return true;
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
LexicalContext context = contextStack.getFirst();
switch (n.getToken()) {
case FUNCTION:
checkState(
context.function == n,
"unexpected function context:\nexpected: %s\nactual: %s",
n,
context.function);
checkState(contextStack.removeFirst() == context);
if (context.isAsyncContext()) {
convertAsyncFunction(t, context);
}
break;
case NAME:
if (context.mustReplaceThisAndArguments() && n.matchesQualifiedName("arguments")) {
n.setString(ASYNC_ARGUMENTS);
context.recordAsyncArgumentsReplacementWasDone();
compiler.reportChangeToChangeScope(context.function);
}
break;
case THIS:
if (context.mustReplaceThisAndArguments()) {
parent.replaceChild(n, context.createThisVariableReference());
compiler.reportChangeToChangeScope(context.function);
}
break;
case SUPER:
if (context.mustReplaceThisAndArguments()) {
if (!parent.isGetProp()) {
compiler.report(
JSError.make(parent, Es6ToEs3Util.CANNOT_CONVERT_YET, "super expression"));
}
// different name for parent for better readability
Node superDotProperty = parent;
SuperPropertyWrapperInfo superPropertyWrapperInfo =
context.getOrCreateSuperPropertyWrapperInfo(superDotProperty);
// super.x => $jscomp$super$get$x()
Node getPropReplacement = superPropertyWrapperInfo.createWrapperFunctionCallNode();
Node grandparent = superDotProperty.getParent();
if (grandparent.isCall() && grandparent.getFirstChild() == superDotProperty) {
// $jscomp$super$get$x(...) => $jscomp$super$get$x().call($jscomp$async$this, ...)
getPropReplacement = astFactory.createGetProp(getPropReplacement, "call");
grandparent.addChildAfter(
astFactory
.createThisAliasReferenceForFunction(ASYNC_THIS, context.function)
.useSourceInfoFrom(superDotProperty),
superDotProperty);
context.recordAsyncThisReplacementWasDone();
}
getPropReplacement.useSourceInfoFromForTree(superDotProperty);
grandparent.replaceChild(superDotProperty, getPropReplacement);
compiler.reportChangeToChangeScope(context.function);
}
break;
case AWAIT:
checkState(context.isAsyncContext(), "await found within non-async function body");
checkState(n.hasOneChild(), "await should have 1 operand, but has %s", n.getChildCount());
// Awaits become yields in the converted async function's inner generator function.
parent.replaceChild(n, astFactory.createYield(n.getJSType(), n.removeFirstChild()));
break;
default:
break;
}
}
private void convertAsyncFunction(NodeTraversal t, LexicalContext functionContext) {
Node originalFunction = checkNotNull(functionContext.function);
originalFunction.setIsAsyncFunction(false);
Node originalBody = originalFunction.getLastChild();
if (originalFunction.isFromExterns()) {
// A function defined in externs will never be executed, so we don't need to transpile it.
// Make sure it has an empty body though so later passes won't trip over uses of `await` or
// anything like that.
if (!NodeUtil.isEmptyBlock(originalBody)) {
// TODO(b/119685646): Maybe we should warn for non-empty functions in externs?
originalBody.replaceWith(astFactory.createBlock());
NodeUtil.markFunctionsDeleted(originalBody, compiler);
}
return;
}
Node newBody = astFactory.createBlock();
originalFunction.replaceChild(originalBody, newBody);
if (functionContext.mustAddAsyncThisVariable) {
// const this$ = this;
newBody.addChildToBack(
astFactory.createThisAliasDeclarationForFunction(ASYNC_THIS, functionContext.function));
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.CONST_DECLARATIONS);
}
if (functionContext.mustAddAsyncArgumentsVariable) {
// const arguments$ = arguments;
newBody.addChildToBack(astFactory.createArgumentsAliasDeclaration(ASYNC_ARGUMENTS));
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.CONST_DECLARATIONS);
}
for (SuperPropertyWrapperInfo superPropertyWrapperInfo :
functionContext.superPropertyWrappers.asCollection()) {
Node arrowFunction = functionContext.createWrapperArrowFunction(superPropertyWrapperInfo);
// const super$get$x = () => super.x;
Node arrowFunctionDeclarationStatement =
astFactory.createSingleConstNameDeclaration(
superPropertyWrapperInfo.wrapperFunctionName, arrowFunction);
newBody.addChildToBack(arrowFunctionDeclarationStatement);
// Make sure the compiler knows about the new arrow function's scope
compiler.reportChangeToChangeScope(arrowFunction);
// Record that we've added arrow functions and const declarations to this script,
// so later transpilations of those features will run, if needed.
Node enclosingScript = t.getCurrentScript();
NodeUtil.addFeatureToScript(enclosingScript, Feature.ARROW_FUNCTIONS);
NodeUtil.addFeatureToScript(enclosingScript, Feature.CONST_DECLARATIONS);
}
// Normalize arrow function short body to block body
if (!originalBody.isBlock()) {
originalBody =
astFactory
.createBlock(astFactory.createReturn(originalBody))
.useSourceInfoIfMissingFromForTree(originalBody);
}
// NOTE: visit() will already have made appropriate replacements in originalBody so it may
// be used as the generator function body.
Node generatorFunction =
astFactory.createZeroArgGeneratorFunction("", originalBody, originalFunction.getJSType());
compiler.reportChangeToChangeScope(generatorFunction);
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.GENERATORS);
// return $jscomp.asyncExecutePromiseGeneratorFunction(function* () { ... });
newBody.addChildToBack(
astFactory.createReturn(
astFactory.createJscompAsyncExecutePromiseGeneratorFunctionCall(
t.getScope(), generatorFunction)));
newBody.useSourceInfoIfMissingFromForTree(originalBody);
compiler.reportChangeToEnclosingScope(newBody);
}
}