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/*
* Copyright 2008 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 com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.rhino.Node;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.function.Supplier;
/**
* RenameLabels renames all the labels so that they have short names, to reduce code size and also
* to obfuscate the code.
*
* Label names have a unique namespace, so variable or function names clashes are not a concern,
* but keywords clashes are.
*
*
Additionally, labels names are only within the statements include in the label and do not
* cross function boundaries. This means that it is possible to create one label name that is used
* for labels at any given depth of label nesting. Typically, the name "a" will be used for all
* top-level labels, "b" for the next nested label, and so on. For example:
* function bar() {
* a: {
* b: {
* foo();
* }
* }
*
* a: {
* b: break a;
* }
* }
* The general processes is as follows: process() is the entry point for the CompilerPass,
* and from there a standard "ScopedCallback" traversal is done, where "shouldTraverse" is called
* when descending the tree, and the "visit" is called in a depth first manner. The name for the
* label is selected during the decent in "shouldTraverse", and the references to the label name are
* renamed as they are encountered during the "visit". This means that if the label is unreferenced,
* it is known when the label node is visited, and, if so, can be safely removed.
*/
final class RenameLabels implements CompilerPass {
private final AbstractCompiler compiler;
private final Supplier nameSupplier;
private final boolean removeUnused;
private final boolean markChanges;
RenameLabels(final AbstractCompiler compiler) {
this(compiler, new DefaultNameSupplier(), true, true);
}
RenameLabels(
AbstractCompiler compiler,
Supplier supplier,
boolean removeUnused,
boolean markChanges) {
this.compiler = compiler;
this.nameSupplier = supplier;
this.removeUnused = removeUnused;
this.markChanges = markChanges;
}
static class DefaultNameSupplier implements Supplier {
// DefaultNameGenerator is used to create safe label names.
private final NameGenerator nameGenerator;
private DefaultNameSupplier() {
this.nameGenerator = new DefaultNameGenerator(new LinkedHashSet(), "", null);
}
@Override
public String get() {
return nameGenerator.generateNextName();
}
}
/** Iterate through the nodes, renaming all the labels. */
class ProcessLabels implements ScopedCallback {
private final boolean markChanges;
ProcessLabels(boolean markChanges) {
this.markChanges = markChanges;
// Create a entry for global scope.
namespaceStack.push(new LabelNamespace());
}
// A stack of labels namespaces. Labels in an outer scope aren't part of an
// inner scope, so a new namespace is created each time a scope is entered.
final Deque namespaceStack = new ArrayDeque<>();
// The list of generated names. Typically, the first name will be "a",
// the second "b", etc.
final ArrayList names = new ArrayList<>();
@Override
public void enterScope(NodeTraversal nodeTraversal) {
// Start a new namespace for label names.
if (nodeTraversal.getScopeRoot().isFunction()) {
namespaceStack.push(new LabelNamespace());
}
}
@Override
public void exitScope(NodeTraversal nodeTraversal) {
if (nodeTraversal.getScopeRoot().isFunction()) {
namespaceStack.pop();
}
}
/**
* shouldTraverse is call when descending into the Node tree, so it is used here to build the
* context for label renames.
*
* {@inheritDoc}
*/
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node node, Node parent) {
if (node.isLabel()) {
// Determine the new name for this label.
LabelNamespace current = namespaceStack.peek();
int currentDepth = current.renameMap.size() + 1;
String name = node.getFirstChild().getString();
// Store the context for this label name.
LabelInfo li = new LabelInfo(currentDepth);
checkState(!current.renameMap.containsKey(name));
current.renameMap.put(name, li);
// Create a new name, if needed, for this depth.
if (names.size() < currentDepth) {
names.add(nameSupplier.get());
}
}
return true;
}
/**
* Delegate the actual processing of the node to visitLabel and visitBreakOrContinue.
*
*
{@inheritDoc}
*/
@Override
public void visit(NodeTraversal t, Node node, Node parent) {
switch (node.getToken()) {
case LABEL:
visitLabel(t, node);
break;
case BREAK:
case CONTINUE:
visitBreakOrContinue(t, node);
break;
default:
break;
}
}
/**
* Rename label references in breaks and continues.
*
* @param node The break or continue node.
*/
private void visitBreakOrContinue(NodeTraversal t, Node node) {
Node nameNode = node.getFirstChild();
if (nameNode != null) {
// This is a named break or continue;
String name = nameNode.getString();
checkState(!name.isEmpty());
LabelInfo li = getLabelInfo(name);
if (li != null) {
String newName = getNameForId(li.id);
// Mark the label as referenced so it isn't removed.
li.referenced = true;
if (!name.equals(newName)) {
// Give it the short name.
nameNode.setString(newName);
if (markChanges) {
t.reportCodeChange();
}
}
}
}
}
/**
* Rename or remove labels.
*
* @param node The label node.
* @param parent The parent of the label node.
*/
private void visitLabel(NodeTraversal t, Node node) {
Node nameNode = node.getFirstChild();
checkState(nameNode != null);
String name = nameNode.getString();
LabelInfo li = getLabelInfo(name);
// This is a label...
if (li.referenced || !removeUnused) {
String newName = getNameForId(li.id);
if (!name.equals(newName)) {
// ... and it is used, give it the short name.
nameNode.setString(newName);
if (markChanges) {
t.reportCodeChange();
}
}
} else {
// ... and it is not referenced, just remove it.
Node newChild = node.getLastChild();
newChild.detach();
node.replaceWith(newChild);
if (newChild.isBlock()) {
NodeUtil.tryMergeBlock(newChild, false);
}
if (markChanges) {
t.reportCodeChange();
}
}
// Remove the label from the current stack of labels.
namespaceStack.peek().renameMap.remove(name);
}
/**
* @param id The id, which is the depth of the label in the current context, for which to get a
* short name.
* @return The short name of the identified label.
*/
String getNameForId(int id) {
return names.get(id - 1);
}
/**
* @param name The name to retrieve information about.
* @return The structure representing the name in the current context.
*/
LabelInfo getLabelInfo(String name) {
return namespaceStack.peek().renameMap.get(name);
}
}
@Override
public void process(Node externs, Node root) {
// Do variable reference counting.
NodeTraversal.traverse(compiler, root, new ProcessLabels(markChanges));
}
private static class LabelInfo {
boolean referenced = false;
final int id;
LabelInfo(int id) {
this.id = id;
}
}
private static class LabelNamespace {
final Map renameMap = new LinkedHashMap<>();
}
}