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/*
* 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 static com.google.javascript.jscomp.AstFactory.type;
import com.google.javascript.jscomp.colors.Color;
import com.google.javascript.jscomp.colors.StandardColors;
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.StaticScope;
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 org.jspecify.nullness.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, CompilerPass {
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$";
private final StaticScope namespace;
/**
* 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.
private final AstFactory.@Nullable Type wrapperFunctionReturnType;
private SuperPropertyWrapperInfo(
Node firstSuperDotPropertyNode,
String wrapperFunctionName,
AstFactory.Type wrapperFunctionReturnType) {
this.firstInstanceOfSuperDotProperty = firstSuperDotPropertyNode;
this.wrapperFunctionName = wrapperFunctionName;
this.wrapperFunctionReturnType = wrapperFunctionReturnType;
}
private @Nullable Color getPropertyType() {
return firstInstanceOfSuperDotProperty.getColor();
}
private Node createWrapperFunctionNameNode() {
return astFactory.createName(wrapperFunctionName, type(StandardColors.TOP_OBJECT));
}
private Node createWrapperFunctionCallNode() {
return astFactory.createCall(createWrapperFunctionNameNode(), wrapperFunctionReturnType);
}
}
/**
* 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 Colors 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);
String propertyName = superDotPropertyNode.getString();
Color propertyType = superDotPropertyNode.getColor();
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.
Color existingColor = superPropertyWrapperInfo.getPropertyType();
checkState(
Objects.equals(existingColor, propertyType),
"Previous reference type: %s differs from current reference type: %s",
existingColor,
propertyType);
} else {
superPropertyWrapperInfo = createNewInfo(superDotPropertyNode);
propertyNameToTypeMap.put(propertyName, superPropertyWrapperInfo);
}
return superPropertyWrapperInfo;
}
private SuperPropertyWrapperInfo createNewInfo(Node firstSuperDotPropertyNode) {
checkArgument(firstSuperDotPropertyNode.isGetProp(), firstSuperDotPropertyNode);
String propertyName = firstSuperDotPropertyNode.getString();
final String wrapperFunctionName = ASYNC_SUPER_PROP_GETTER_PREFIX + propertyName;
return new SuperPropertyWrapperInfo(
firstSuperDotPropertyNode, wrapperFunctionName, type(firstSuperDotPropertyNode));
}
private Collection asCollection() {
return propertyNameToTypeMap.values();
}
}
/**
* Determines both what to do when visiting a node and how to determine the context for its
* descendents.
*/
private abstract static class LexicalContext {
final Node contextRootNode;
LexicalContext(Node contextRootNode) {
this.contextRootNode = checkNotNull(contextRootNode);
}
Node getContextRootNode() {
return contextRootNode;
}
/**
* Returns the LexicalContext to use for visiting a node.
*
* @param n This context's root node or one of its descendents.
* @return this context or a new one for a child context
*/
public abstract LexicalContext getContextForNode(Node n);
public abstract void visit(NodeTraversal t, Node n);
}
/** Defines behavior for nodes in the root scope, outside of any functions. */
private final class RootContext extends LexicalContext {
private RootContext(Node contextRootNode) {
super(contextRootNode);
}
@Override
public LexicalContext getContextForNode(Node n) {
if (n.isFunction()) {
return new FunctionContext(n);
} else {
return this;
}
}
@Override
public void visit(NodeTraversal t, Node n) {
// In root context we haven't entered an async function yet, so there's nothing to do.
}
}
/** Defines the behavior for function definition parameter lists and their contents. */
private final class ParameterListContext extends LexicalContext {
final FunctionContext functionContext;
public ParameterListContext(FunctionContext functionContext, Node contextRootNode) {
super(contextRootNode);
this.functionContext = checkNotNull(functionContext);
}
@Override
public LexicalContext getContextForNode(Node n) {
if (n.isFunction()) {
// Function defined within a parameter list.
// e.g. `() => something`
// function someFunc(callback = () => something) {}
return new FunctionContext(functionContext, n);
} else {
return this;
}
}
@Override
public void visit(NodeTraversal t, Node n) {
if (functionContext.asyncThisAndArgumentsContext != null
&& functionContext.asyncThisAndArgumentsContext != functionContext) {
// e.g.
// async function outer(outerT = this) {
// // `this` in outer parameter list must remain unchanged
// // but inner parameter list must be aliased
// const inner = async (t = this) => t;
// }
functionContext.visit(t, n);
}
}
}
/**
* Defines behavior for replacing references to `this`, `arguments`, and `super` within async
* functions and rewriting the async functions themselves.
*/
private final class FunctionContext extends LexicalContext {
// If references to `this`, `arguments`, and `super` should be considered in the context of
// an async function, this will point to that function's FunctionContext.
// Otherwise, it will be `null`.
// TODO(bradfordcsmith): It would cost less memory if we defined a separate object to hold
// the data for async context accounting instead of having the booleans and super property
// wrapper fields on every FunctionContext.
final @Nullable FunctionContext asyncThisAndArgumentsContext;
final SuperPropertyWrappers superPropertyWrappers = new SuperPropertyWrappers();
boolean mustAddAsyncThisVariable = false;
// null if mustAddAsyncThisVariable is false
AstFactory.@Nullable Type typeOfThis;
boolean mustAddAsyncArgumentsVariable = false;
FunctionContext(Node contextRootNode) {
super(contextRootNode);
if (contextRootNode.isAsyncFunction()) {
asyncThisAndArgumentsContext = this;
} else {
asyncThisAndArgumentsContext = null;
}
}
FunctionContext(FunctionContext outer, Node contextRootNode) {
super(contextRootNode);
checkState(contextRootNode.isFunction(), contextRootNode);
if (contextRootNode.isAsyncFunction()) {
if (contextRootNode.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 (contextRootNode.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;
}
}
}
@Override
public LexicalContext getContextForNode(Node n) {
if (n == contextRootNode) {
return this;
} else if (n.isFunction()) {
return new FunctionContext(this, n);
} else if (n.isParamList()) {
return new ParameterListContext(this, n);
} else {
return this;
}
}
private void recordAsyncThisReplacementWasDone(AstFactory.Type typeOfThis) {
asyncThisAndArgumentsContext.mustAddAsyncThisVariable = true;
asyncThisAndArgumentsContext.typeOfThis = typeOfThis;
}
private SuperPropertyWrapperInfo getOrCreateSuperPropertyWrapperInfo(
Node superDotPropertyNode) {
return asyncThisAndArgumentsContext.superPropertyWrappers.getOrCreateSuperPropertyWrapperInfo(
superDotPropertyNode);
}
private void recordAsyncArgumentsReplacementWasDone() {
asyncThisAndArgumentsContext.mustAddAsyncArgumentsVariable = true;
}
/**
* Creates a new reference to the variable used to hold the value of `this` for async functions.
*/
private Node createThisVariableReference(AstFactory.Type typeOfThis) {
recordAsyncThisReplacementWasDone(typeOfThis);
return astFactory.createName(ASYNC_THIS, typeOfThis);
}
private Node createWrapperArrowFunction(SuperPropertyWrapperInfo wrapperInfo) {
// super.propertyName
final Node superDotProperty = wrapperInfo.firstInstanceOfSuperDotProperty.cloneTree();
// () => super.propertyName
return astFactory.createZeroArgArrowFunctionForExpression(superDotProperty);
}
@Override
public void visit(NodeTraversal t, Node n) {
if (contextRootNode == n && contextRootNode.isAsyncFunction()) {
// We're visiting an async function.
// All of its descendent nodes will have been updated as necessary, so now we just need to
// convert the function itself.
convertAsyncFunction(t, this);
} else if (asyncThisAndArgumentsContext != null) {
// We're in the context of an async function's body, so we need to do some replacements.
switch (n.getToken()) {
case NAME:
if (n.matchesName("arguments")) {
n.setString(ASYNC_ARGUMENTS);
asyncThisAndArgumentsContext.recordAsyncArgumentsReplacementWasDone();
compiler.reportChangeToChangeScope(contextRootNode);
}
break;
case THIS:
n.replaceWith(asyncThisAndArgumentsContext.createThisVariableReference(type(n)));
compiler.reportChangeToChangeScope(contextRootNode);
break;
case SUPER:
{
Node parent = n.getParent();
if (!parent.isGetProp()) {
compiler.report(
JSError.make(parent, TranspilationUtil.CANNOT_CONVERT_YET, "super expression"));
}
// different name for parent for better readability
Node superDotProperty = parent;
SuperPropertyWrapperInfo superPropertyWrapperInfo =
asyncThisAndArgumentsContext.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.createGetPropWithUnknownType(getPropReplacement, "call");
Node thisAlias =
astFactory
.createThisAliasReferenceForEs6Class(
ASYNC_THIS,
NodeUtil.getEnclosingClass(
asyncThisAndArgumentsContext.getContextRootNode()))
.srcref(superDotProperty);
thisAlias.insertAfter(superDotProperty);
asyncThisAndArgumentsContext.recordAsyncThisReplacementWasDone(type(thisAlias));
}
getPropReplacement.srcrefTree(superDotProperty);
superDotProperty.replaceWith(getPropReplacement);
compiler.reportChangeToChangeScope(contextRootNode);
}
break;
case AWAIT:
// Awaits become yields in the converted async function's inner generator function.
n.replaceWith(astFactory.createYield(type(n), n.removeFirstChild()));
break;
default:
break;
}
}
}
}
private static final FeatureSet transpiledFeatures =
FeatureSet.BARE_MINIMUM.with(Feature.ASYNC_FUNCTIONS);
private final Deque contextStack;
private final AbstractCompiler compiler;
private final AstFactory astFactory;
private RewriteAsyncFunctions(
AbstractCompiler compiler, AstFactory astFactory, StaticScope namespace) {
this.compiler = checkNotNull(compiler);
this.astFactory = checkNotNull(astFactory);
this.namespace = checkNotNull(namespace);
this.contextStack = new ArrayDeque<>();
}
static RewriteAsyncFunctions create(AbstractCompiler compiler) {
AstFactory astFactory = compiler.createAstFactory();
StaticScope namespace = compiler.getTranspilationNamespace();
return new RewriteAsyncFunctions(compiler, astFactory, namespace);
}
@Override
public void process(Node externs, Node root) {
TranspilationPasses.processTranspile(compiler, root, transpiledFeatures, this);
TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
}
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
if (parent == null) {
checkState(contextStack.isEmpty());
contextStack.push(new RootContext(n));
} else {
LexicalContext parentContext = contextStack.peek();
LexicalContext nodeContext = parentContext.getContextForNode(n);
if (nodeContext != parentContext) {
contextStack.push(nodeContext);
}
}
return true;
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
LexicalContext context = contextStack.peek();
context.visit(t, n);
if (context.getContextRootNode() == n) {
contextStack.pop();
}
}
private void convertAsyncFunction(NodeTraversal t, FunctionContext functionContext) {
Node originalFunction = functionContext.getContextRootNode();
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();
originalBody.replaceWith(newBody);
if (functionContext.mustAddAsyncThisVariable) {
// const this$ = this;
newBody.addChildToBack(
astFactory.createSingleConstNameDeclaration(
ASYNC_THIS, astFactory.createThis(functionContext.typeOfThis)));
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.CONST_DECLARATIONS, compiler);
}
if (functionContext.mustAddAsyncArgumentsVariable) {
// const arguments$ = arguments;
newBody.addChildToBack(astFactory.createArgumentsAliasDeclaration(ASYNC_ARGUMENTS));
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.CONST_DECLARATIONS, compiler);
}
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, compiler);
NodeUtil.addFeatureToScript(enclosingScript, Feature.CONST_DECLARATIONS, compiler);
}
// Normalize arrow function short body to block body
if (!originalBody.isBlock()) {
originalBody =
astFactory
.createBlock(astFactory.createReturn(originalBody))
.srcrefTreeIfMissing(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, /* returnType= */ null);
compiler.reportChangeToChangeScope(generatorFunction);
NodeUtil.addFeatureToScript(t.getCurrentScript(), Feature.GENERATORS, compiler);
// return $jscomp.asyncExecutePromiseGeneratorFunction(function* () { ... });
newBody.addChildToBack(
astFactory.createReturn(
astFactory.createJscompAsyncExecutePromiseGeneratorFunctionCall(
namespace, generatorFunction)));
newBody.srcrefTreeIfMissing(originalBody);
compiler.reportChangeToEnclosingScope(newBody);
}
}