com.google.javascript.jscomp.Es6RewriteBlockScopedDeclaration Maven / Gradle / Ivy
/*
* Copyright 2014 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.checkState;
import static com.google.javascript.jscomp.AstFactory.type;
import com.google.common.base.Predicate;
import com.google.common.base.Supplier;
import com.google.common.collect.HashBasedTable;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.Multimap;
import com.google.common.collect.Table;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
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.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import org.jspecify.nullness.Nullable;
/**
* Rewrite "let"s and "const"s as "var"s. Rename block-scoped declarations and their references when
* necessary.
*
* Note that this must run after Es6RewriteDestructuring, since it does not process destructuring
* let/const declarations at all.
*
*
TODO(moz): Try to use MakeDeclaredNamesUnique
*/
public final class Es6RewriteBlockScopedDeclaration extends AbstractPostOrderCallback
implements CompilerPass {
private final AbstractCompiler compiler;
private final AstFactory astFactory;
private final Table renameTable = HashBasedTable.create();
private final Set letConsts = new HashSet<>();
private final Set undeclaredNames = new HashSet<>();
private final Set externNames = new HashSet<>();
private static final FeatureSet transpiledFeatures =
FeatureSet.BARE_MINIMUM.with(Feature.LET_DECLARATIONS, Feature.CONST_DECLARATIONS);
private final Supplier uniqueNameIdSupplier;
public Es6RewriteBlockScopedDeclaration(AbstractCompiler compiler) {
this.compiler = compiler;
this.uniqueNameIdSupplier = compiler.getUniqueNameIdSupplier();
this.astFactory = compiler.createAstFactory();
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (!n.hasChildren() || !NodeUtil.isBlockScopedDeclaration(n.getFirstChild())) {
return;
}
// NOTE: This pass depends on for-of being transpiled away before it runs.
checkState(parent == null || !parent.isForOf(), parent);
if (n.isLet() || n.isConst()) {
letConsts.add(n);
}
if (NodeUtil.isNameDeclaration(n)) {
for (Node nameNode = n.getFirstChild(); nameNode != null; nameNode = nameNode.getNext()) {
visitBlockScopedName(t, n, nameNode);
}
} else {
// NOTE: This pass depends on class declarations having been transpiled away
checkState(n.isFunction() || n.isCatch(), "Unexpected declaration node: %s", n);
visitBlockScopedName(t, n, n.getFirstChild());
}
}
@Override
public void process(Node externs, Node root) {
NodeTraversal.traverse(compiler, root, new CollectUndeclaredNames());
// Record names declared in externs to prevent collisions when declaring vars from let/const.
this.externNames.addAll(NodeUtil.collectExternVariableNames(compiler, externs));
NodeTraversal.traverse(compiler, root, this);
NodeTraversal.traverse(compiler, root, new Es6RenameReferences(renameTable));
LoopClosureTransformer transformer = new LoopClosureTransformer();
NodeTraversal.traverse(compiler, root, transformer);
transformer.transformLoopClosure();
rewriteDeclsToVars();
TranspilationPasses.maybeMarkFeaturesAsTranspiledAway(compiler, transpiledFeatures);
}
/**
* Renames block-scoped declarations that shadow a variable in an outer scope
*
* Also normalizes declarations with no initializer in a loop to be initialized to undefined.
*/
private void visitBlockScopedName(NodeTraversal t, Node decl, Node nameNode) {
Scope scope = t.getScope();
Node parent = decl.getParent();
// Normalize "let x;" to "let x = undefined;" if in a loop, since we later convert x
// to be $jscomp$loop$0.x and want to reset the property to undefined every loop iteration.
if ((decl.isLet() || decl.isConst())
&& !nameNode.hasChildren()
&& (parent == null || !parent.isForIn())
&& inLoop(decl)) {
Node undefined = astFactory.createUndefinedValue().srcrefTree(nameNode);
nameNode.addChildToFront(undefined);
compiler.reportChangeToEnclosingScope(undefined);
}
String oldName = nameNode.getString();
Scope hoistScope = scope.getClosestHoistScope();
if (scope != hoistScope) {
String newName = oldName;
if (hoistScope.hasSlot(oldName)
|| undeclaredNames.contains(oldName)
|| externNames.contains(oldName)) {
do {
newName = oldName + "$" + compiler.getUniqueNameIdSupplier().get();
} while (hoistScope.hasSlot(newName));
nameNode.setString(newName);
compiler.reportChangeToEnclosingScope(nameNode);
Node scopeRoot = scope.getRootNode();
renameTable.put(scopeRoot, oldName, newName);
}
Var oldVar = scope.getVar(oldName);
scope.undeclare(oldVar);
hoistScope.declare(newName, nameNode, oldVar.getInput());
}
}
/**
* Whether n is inside a loop. If n is inside a function which is inside a loop, we do not
* consider it to be inside a loop.
*/
private boolean inLoop(Node n) {
Node enclosingNode = NodeUtil.getEnclosingNode(n, isLoopOrFunction);
return enclosingNode != null && !enclosingNode.isFunction();
}
private static final Predicate isLoopOrFunction =
new Predicate() {
@Override
public boolean apply(Node n) {
return n.isFunction() || NodeUtil.isLoopStructure(n);
}
};
private static void extractInlineJSDoc(Node srcDeclaration, Node srcName, Node destDeclaration) {
JSDocInfo existingInfo = srcDeclaration.getJSDocInfo();
if (existingInfo == null) {
// Extract inline JSDoc from "src" and add it to the "dest" node.
existingInfo = srcName.getJSDocInfo();
srcName.setJSDocInfo(null);
}
JSDocInfo.Builder builder = JSDocInfo.Builder.maybeCopyFrom(existingInfo);
destDeclaration.setJSDocInfo(builder.build());
}
private static void maybeAddConstJSDoc(Node srcDeclaration, Node srcName, Node destDeclaration) {
if (srcDeclaration.isConst()) {
extractInlineJSDoc(srcDeclaration, srcName, destDeclaration);
JSDocInfo.Builder builder = JSDocInfo.Builder.maybeCopyFrom(destDeclaration.getJSDocInfo());
builder.recordConstancy();
destDeclaration.setJSDocInfo(builder.build());
}
}
private void handleDeclarationList(Node declarationList, Node parent) {
// Normalize: "const i = 0, j = 0;" becomes "/** @const */ var i = 0; /** @const */ var j = 0;"
while (declarationList.hasMoreThanOneChild()) {
Node name = declarationList.getLastChild();
Node newDeclaration = IR.var(name.detach()).srcref(declarationList);
maybeAddConstJSDoc(declarationList, name, newDeclaration);
newDeclaration.insertAfter(declarationList);
compiler.reportChangeToEnclosingScope(parent);
}
maybeAddConstJSDoc(declarationList, declarationList.getFirstChild(), declarationList);
declarationList.setToken(Token.VAR);
}
private void addNodeBeforeLoop(Node newNode, Node loopNode) {
Node insertSpot = loopNode;
while (insertSpot.getParent().isLabel()) {
insertSpot = insertSpot.getParent();
}
newNode.insertBefore(insertSpot);
compiler.reportChangeToEnclosingScope(newNode);
}
private void rewriteDeclsToVars() {
if (!letConsts.isEmpty()) {
for (Node n : letConsts) {
if (n.isConst()) {
handleDeclarationList(n, n.getParent());
}
n.setToken(Token.VAR);
compiler.reportChangeToEnclosingScope(n);
}
}
}
/**
* Records undeclared names and aggressively rename possible references to them. Eg: In "{ let
* inner; } use(inner);", we rename the let declared variable.
*/
private class CollectUndeclaredNames extends AbstractPostOrderCallback {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isName() && !t.getScope().hasSlot(n.getString())) {
undeclaredNames.add(n.getString());
}
}
}
/** Transforms let/const declarations captured by loop closures. */
private class LoopClosureTransformer extends AbstractPostOrderCallback {
private static final String LOOP_OBJECT_NAME = "$jscomp$loop";
private static final String LOOP_OBJECT_PROPERTY_NAME = "$jscomp$loop$prop$";
private final Map loopObjectMap = new LinkedHashMap<>();
private final Multimap functionLoopObjectsMap = LinkedHashMultimap.create();
private final Multimap functionHandledMap = HashMultimap.create();
private final Multimap referenceMap = LinkedHashMultimap.create();
// Maps from a var to a unique property name for that var
// e.g. 'i' -> '$jscomp$loop$prop$i$0'
private final Map propertyNameMap = new LinkedHashMap<>();
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (!NodeUtil.isReferenceName(n)) {
return;
}
String name = n.getString();
Scope referencedIn = t.getScope();
Var var = referencedIn.getVar(name);
if (var == null) {
return;
}
if (!var.isLet() && !var.isConst()) {
return;
}
if (n.getParent().isLet() || n.getParent().isConst()) {
letConsts.add(n.getParent());
}
// Traverse nodes up from let/const declaration:
// If we hit a function or the root before a loop - Not a loop closure.
// if we hit a loop first - maybe loop closure.
Scope declaredIn = var.getScope();
Node loopNode = null;
for (Scope s = declaredIn; ; s = s.getParent()) {
Node scopeRoot = s.getRootNode();
if (NodeUtil.isLoopStructure(scopeRoot)) {
loopNode = scopeRoot;
break;
} else if (scopeRoot.hasParent() && NodeUtil.isLoopStructure(scopeRoot.getParent())) {
loopNode = scopeRoot.getParent();
break;
} else if (s.isFunctionBlockScope() || s.isGlobal()) {
return;
}
}
referenceMap.put(var, n);
// Traverse scopes from reference scope to declaration scope.
// If we hit a function - loop closure detected.
Scope outerMostFunctionScope = null;
for (Scope s = referencedIn;
s != declaredIn && s.getRootNode() != loopNode;
s = s.getParent()) {
if (s.isFunctionScope()) {
outerMostFunctionScope = s;
}
}
if (outerMostFunctionScope != null) {
Node function = outerMostFunctionScope.getRootNode();
if (functionHandledMap.containsEntry(function, name)) {
return;
}
functionHandledMap.put(function, name);
LoopObject object =
loopObjectMap.computeIfAbsent(
loopNode,
(Node k) ->
new LoopObject(
LOOP_OBJECT_NAME + "$" + compiler.getUniqueNameIdSupplier().get()));
String newPropertyName = createUniquePropertyName(var);
object.vars.add(var);
propertyNameMap.put(var, newPropertyName);
functionLoopObjectsMap.put(function, object);
}
}
private String createUniquePropertyName(Var var) {
return LOOP_OBJECT_PROPERTY_NAME + var.getName() + "$" + uniqueNameIdSupplier.get();
}
private void transformLoopClosure() {
if (loopObjectMap.isEmpty()) {
return;
}
for (Node loopNode : loopObjectMap.keySet()) {
// Introduce objects to reflect the captured scope variables.
// Fields are initially left as undefined to avoid cases like:
// var $jscomp$loop$0 = {$jscomp$loop$prop$i: 0, $jscomp$loop$prop$j: $jscomp$loop$0.i}
// They are initialized lazily by changing declarations into assignments
// later.
LoopObject loopObject = loopObjectMap.get(loopNode);
Node objectLitNextIteration = astFactory.createObjectLit();
for (Var var : loopObject.vars) {
String newPropertyName = propertyNameMap.get(var);
objectLitNextIteration.addChildToBack(
astFactory.createStringKey(
newPropertyName,
createLoopVarReferenceReplacement(
loopObject, var.getNameNode(), newPropertyName)));
}
Node updateLoopObject =
astFactory.createAssign(createLoopObjectNameNode(loopObject), objectLitNextIteration);
Node objectLit =
IR.var(createLoopObjectNameNode(loopObject), astFactory.createObjectLit())
.srcrefTree(loopNode);
addNodeBeforeLoop(objectLit, loopNode);
if (loopNode.isVanillaFor()) { // For
// The initializer is pulled out and placed prior to the loop.
Node initializer = loopNode.getFirstChild();
initializer.replaceWith(IR.empty());
if (!initializer.isEmpty()) {
if (!NodeUtil.isNameDeclaration(initializer)) {
initializer = IR.exprResult(initializer).srcref(initializer);
}
addNodeBeforeLoop(initializer, loopNode);
}
Node increment = loopNode.getChildAtIndex(2);
if (increment.isEmpty()) {
increment.replaceWith(updateLoopObject.srcrefTreeIfMissing(loopNode));
} else {
Node placeHolder = IR.empty();
increment.replaceWith(placeHolder);
placeHolder.replaceWith(
astFactory.createComma(updateLoopObject, increment).srcrefTreeIfMissing(loopNode));
}
} else {
// We need to make sure the loop object update happens on every loop iteration.
// We want to keep it at the end of the loop, because that makes it easier to reason
// about the types.
//
// TODO(bradfordcsmith): Maybe move the update to the start of the loop when this pass
// is moved after the type checking passes.
//
// A finally block would do it, but would have more runtime cost, so instead, if we find
// that there are continue statements referring to the loop we will do this.
//
// originalLoopLabel: while (condition) {
// $jscomp$loop$0: {
// // original loop body here
// // with continue statements converted to `break $jscomp$loop$0;`
// // If originalLoopLabel exists, we'll also need to traverse into innner loops
// // and convert `continue originalLoopLabel;`.
// }
// $jscomp$loop$0 = { var1: $jscomp$loop$0.var1, var2: $jscomp$loop$0.var2, ... };
// }
// We're intentionally using the same name for the inner loop label and the loop variable
// object. Label names and variables are different namespaces, so they do not conflict.
String innerBlockLabel = loopObject.name;
Node loopBody = NodeUtil.getLoopCodeBlock(loopNode);
if (maybeUpdateContinueStatements(loopNode, innerBlockLabel)) {
Node innerBlock = IR.block().srcref(loopBody);
innerBlock.addChildrenToFront(loopBody.removeChildren());
loopBody.addChildToFront(
IR.label(IR.labelName(innerBlockLabel).srcref(loopBody), innerBlock)
.srcref(loopBody));
}
loopBody.addChildToBack(IR.exprResult(updateLoopObject).srcrefTreeIfMissing(loopNode));
}
compiler.reportChangeToEnclosingScope(loopNode);
// For captured variables, change declarations to assignments on the
// corresponding field of the introduced object. Rename all references
// accordingly.
for (Var var : loopObject.vars) {
String newPropertyName = propertyNameMap.get(var);
for (Node reference : referenceMap.get(var)) {
// for-of loops are transpiled away before this pass runs
checkState(!loopNode.isForOf(), loopNode);
// For-of and for-in declarations are not altered, since they are
// used as temporary variables for assignment.
if (loopNode.isForIn() && loopNode.getFirstChild() == reference.getParent()) {
// reference is the node loopVar in a for-in or for-of that looks like this:
// `for (const loopVar of list) {`
checkState(reference == var.getNameNode(), reference);
Node referenceParent = reference.getParent();
checkState(NodeUtil.isNameDeclaration(referenceParent), referenceParent);
checkState(reference.isName(), reference);
// Start transpiled form of
// `for (const p in obj) { ... }`
// with this statement to copy the loop variable into the corresponding loop object
// property.
// `$jscomp$loop$0.$jscomp$loop$prop$0$p = p;`
Node loopVarReference = reference.cloneNode();
loopNode
.getLastChild()
.addChildToFront(
IR.exprResult(
astFactory.createAssign(
createLoopVarReferenceReplacement(
loopObject, reference, newPropertyName),
loopVarReference))
.srcrefTreeIfMissing(reference));
} else {
if (NodeUtil.isNameDeclaration(reference.getParent())) {
Node declaration = reference.getParent();
Node grandParent = declaration.getParent();
handleDeclarationList(declaration, grandParent);
declaration = reference.getParent(); // Might have changed after normalization.
// Change declaration to assignment, or just drop it if there's
// no initial value.
if (reference.hasChildren()) {
Node newReference = cloneWithType(reference);
Node assign = astFactory.createAssign(newReference, reference.removeFirstChild());
extractInlineJSDoc(declaration, reference, declaration);
maybeAddConstJSDoc(declaration, reference, declaration);
assign.setJSDocInfo(declaration.getJSDocInfo());
Node replacement = IR.exprResult(assign).srcrefTreeIfMissing(declaration);
declaration.replaceWith(replacement);
reference = newReference;
} else {
declaration.detach();
}
letConsts.remove(declaration);
compiler.reportChangeToEnclosingScope(grandParent);
}
if (reference.getParent().isCall()
&& reference.getParent().getFirstChild() == reference) {
reference.getParent().putBooleanProp(Node.FREE_CALL, false);
}
// Change reference to GETPROP.
Node changeScope = NodeUtil.getEnclosingChangeScopeRoot(reference);
reference.replaceWith(
createLoopVarReferenceReplacement(loopObject, reference, newPropertyName));
// TODO(johnlenz): Don't work on detached nodes.
if (changeScope != null) {
compiler.reportChangeToChangeScope(changeScope);
}
}
}
}
}
// Create wrapper functions and call them.
for (Node function : functionLoopObjectsMap.keySet()) {
Node returnNode = IR.returnNode();
Collection objects = functionLoopObjectsMap.get(function);
Node[] objectNames = new Node[objects.size()];
Node[] objectNamesForCall = new Node[objects.size()];
int i = 0;
for (LoopObject object : objects) {
Node paramObjectName = createLoopObjectNameNode(object);
objectNames[i] = paramObjectName;
objectNamesForCall[i] = createLoopObjectNameNode(object);
i++;
}
Node iife =
astFactory.createFunction(
"",
IR.paramList(objectNames),
IR.block(returnNode),
type(StandardColors.TOP_OBJECT));
compiler.reportChangeToChangeScope(iife);
Node call = astFactory.createCall(iife, type(function), objectNamesForCall);
call.putBooleanProp(Node.FREE_CALL, true);
Node replacement;
if (NodeUtil.isFunctionDeclaration(function)) {
replacement =
IR.var(IR.name(function.getFirstChild().getString()), call)
.srcrefTreeIfMissing(function);
} else {
replacement = call.srcrefTreeIfMissing(function);
}
function.replaceWith(replacement);
returnNode.addChildToFront(function);
compiler.reportChangeToEnclosingScope(replacement);
}
}
/**
* Creates a `$jscomp$loop$0.$jscomp$loop$prop$varName$1` replacement for a reference to
* `varName`.
*/
private Node createLoopVarReferenceReplacement(
LoopObject loopObject, Node reference, String propertyName) {
Node replacement =
astFactory.createGetProp(
createLoopObjectNameNode(loopObject), propertyName, type(reference));
replacement.srcrefTree(reference);
return replacement;
}
private Node createLoopObjectNameNode(LoopObject loopObject) {
return astFactory.createName(loopObject.name, type(StandardColors.TOP_OBJECT));
}
/**
* Converts all continue statements referring to the given loop to `break $jscomp$loop$0;` where
* `$jscomp$loop$0` is the label on the block containing the original loop body.
*
* If this method returns {@code true}, then we must wrap the original loop body in a block
* labeled with the name from the loopObject.
*
* @return True if at least one continue statement was found and replaced.
*/
private boolean maybeUpdateContinueStatements(Node loopNode, String breakLabel) {
Node loopParent = loopNode.getParent();
final String originalLoopLabel =
loopParent.isLabel() ? loopParent.getFirstChild().getString() : null;
ContinueStatementUpdater continueStatementUpdater =
new ContinueStatementUpdater(breakLabel, originalLoopLabel);
NodeTraversal.traverse(
compiler, NodeUtil.getLoopCodeBlock(loopNode), continueStatementUpdater);
return continueStatementUpdater.replacedAContinueStatement;
}
/**
* Converts all continue statements referring to the given loop to `break $jscomp$loop$0;` where
* `$jscomp$loop$0` is the label on the block containing the original loop body.
*/
private class ContinueStatementUpdater implements NodeTraversal.Callback {
// label to put on break statements created that replace continue statements.
private final String breakLabel;
private final @Nullable String originalLoopLabel;
// Track how many levels of loops deep we go below this one.
int loopDepth = 0;
// Set to true if a continue statement is found
boolean replacedAContinueStatement = false;
public ContinueStatementUpdater(String breakLabel, @Nullable String originalLoopLabel) {
this.breakLabel = breakLabel;
this.originalLoopLabel = originalLoopLabel;
}
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
// NOTE: This pass runs after ES6 classes have already been transpiled away.
checkState(!n.isClass(), n);
if (n.isFunction()) {
return false;
} else if (NodeUtil.isLoopStructure(n)) {
if (originalLoopLabel == null) {
// If this loop has no label, there cannot be any continue statements referring to it
// in inner loops.
return false;
} else {
loopDepth++;
return true;
}
} else {
return true;
}
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (NodeUtil.isLoopStructure(n)) {
loopDepth--;
} else if (n.isContinue()) {
if (loopDepth == 0 && !n.hasChildren()) {
replaceWithBreak(n);
} else if (originalLoopLabel != null
&& n.hasChildren()
&& originalLoopLabel.equals(n.getOnlyChild().getString())) {
replaceWithBreak(n);
} // else continue belongs to some other loop
} // else nothing to do
}
private void replaceWithBreak(Node continueNode) {
Node labelName = IR.labelName(breakLabel).srcref(continueNode);
Node breakNode = IR.breakNode(labelName).srcref(continueNode);
continueNode.replaceWith(breakNode);
replacedAContinueStatement = true;
}
}
private class LoopObject {
/**
* The name of the variable having the loop's internal variables as properties, and the label
* applied to the block containing the original loop body in cases where these are needed.
*/
private final String name;
private final Set vars = new LinkedHashSet<>();
private LoopObject(String name) {
this.name = name;
}
}
}
private Node cloneWithType(Node node) {
Node clone = node.cloneNode();
if (astFactory.isAddingColors()) {
clone.setColor(node.getColor());
}
return clone;
}
}