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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.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.Iterables;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.StaticSymbolTable;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A helper class for passes that want to access all information about where a variable is
* referenced and declared at once and then make a decision as to how it should be handled, possibly
* inlining, reordering, or generating warnings. Callers do this by providing {@link Behavior} and
* then calling {@link #process(Node, Node)}.
*/
public final class ReferenceCollectingCallback
implements ScopedCallback, HotSwapCompilerPass, StaticSymbolTable {
/**
* Maps a given variable to a collection of references to that name. Note that
* Var objects are not stable across multiple traversals (unlike scope root or
* name).
*/
private final Map referenceMap =
new LinkedHashMap<>();
/**
* The stack of basic blocks and scopes the current traversal is in.
*/
private List blockStack = new ArrayList<>();
/**
* Source of behavior at various points in the traversal.
*/
private final Behavior behavior;
private final ScopeCreator scopeCreator;
/**
* JavaScript compiler to use in traversing.
*/
private final AbstractCompiler compiler;
/**
* Only collect references for filtered variables.
*/
private final Predicate varFilter;
/**
* Traverse hoisted functions where they're referenced, not
* where they're declared.
*/
private final Set startedFunctionTraverse = new HashSet<>();
private final Set finishedFunctionTraverse = new HashSet<>();
private Scope narrowScope;
/**
* Constructor initializes block stack.
*/
public ReferenceCollectingCallback(AbstractCompiler compiler, Behavior behavior,
ScopeCreator creator) {
this(compiler, behavior, creator, Predicates.alwaysTrue());
}
/**
* Constructor only collects references that match the given variable.
*
* The test for Var equality uses reference equality, so it's necessary to
* inject a scope when you traverse.
*/
ReferenceCollectingCallback(AbstractCompiler compiler, Behavior behavior, ScopeCreator creator,
Predicate varFilter) {
this.compiler = compiler;
this.behavior = behavior;
this.scopeCreator = creator;
this.varFilter = varFilter;
}
/**
* Convenience method for running this pass over a tree with this
* class as a callback.
*/
@Override
public void process(Node externs, Node root) {
NodeTraversal t = new NodeTraversal(compiler, this, scopeCreator);
t.traverseRoots(externs, root);
}
public void process(Node root) {
NodeTraversal t = new NodeTraversal(compiler, this, scopeCreator);
t.traverse(root);
}
/**
* Targets reference collection to a particular scope.
*/
void processScope(Scope scope) {
boolean shouldAddToBlockStack = !scope.isHoistScope();
this.narrowScope = scope;
if (shouldAddToBlockStack) {
blockStack.add(new BasicBlock(null, scope.getRootNode()));
}
(new NodeTraversal(compiler, this, scopeCreator)).traverseAtScope(scope);
if (shouldAddToBlockStack) {
pop(blockStack);
}
this.narrowScope = null;
}
/**
* Same as process but only runs on a part of AST associated to one script.
*/
@Override
public void hotSwapScript(Node scriptRoot, Node originalRoot) {
NodeTraversal.traverse(compiler, scriptRoot, this);
}
/**
* Gets the variables that were referenced in this callback.
*/
@Override
public Iterable getAllSymbols() {
return referenceMap.keySet();
}
@Override
public Scope getScope(Var var) {
return var.getScope();
}
/**
* Gets the reference collection for the given variable.
*/
@Override
public ReferenceCollection getReferences(Var v) {
return referenceMap.get(v);
}
/**
* For each node, update the block stack and reference collection
* as appropriate.
*/
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isName() || n.isImportStar()) {
if ((parent.isImportSpec() && n != parent.getLastChild())
|| (parent.isExportSpec() && n != parent.getFirstChild())) {
// The n in `import {n as x}` or `export {x as n}` are not references, even though
// they are represented in the AST as NAME nodes.
return;
}
Var v = t.getScope().getVar(n.getString());
if (v != null) {
if (varFilter.apply(v)) {
addReference(v, new Reference(n, t, peek(blockStack)));
}
if (v.getParentNode() != null
&& NodeUtil.isHoistedFunctionDeclaration(v.getParentNode())
// If we're only traversing a narrow scope, do not try to climb outside.
&& (narrowScope == null || narrowScope.getDepth() <= v.getScope().getDepth())) {
outOfBandTraversal(v);
}
}
}
if (isBlockBoundary(n, parent)) {
pop(blockStack);
}
}
private void outOfBandTraversal(Var v) {
if (startedFunctionTraverse.contains(v)) {
return;
}
startedFunctionTraverse.add(v);
Node fnNode = v.getParentNode();
// Replace the block stack with a new one. This algorithm only works
// because we know hoisted functions cannot be inside loops. It will have to
// change if we ever do general function continuations.
checkState(NodeUtil.isHoistedFunctionDeclaration(fnNode), fnNode);
Scope containingScope = v.getScope();
// This is tricky to compute because of the weird traverseAtScope call for
// AggressiveInlineAliases.
List newBlockStack = null;
if (containingScope.isGlobal()) {
newBlockStack = new ArrayList<>();
newBlockStack.add(blockStack.get(0));
} else {
for (int i = 0; i < blockStack.size(); i++) {
if (blockStack.get(i).getRoot() == containingScope.getRootNode()) {
newBlockStack = new ArrayList<>(blockStack.subList(0, i + 1));
}
}
}
checkNotNull(newBlockStack);
List oldBlockStack = blockStack;
blockStack = newBlockStack;
NodeTraversal outOfBandTraversal = new NodeTraversal(compiler, this, scopeCreator);
outOfBandTraversal.traverseFunctionOutOfBand(fnNode, containingScope);
blockStack = oldBlockStack;
finishedFunctionTraverse.add(v);
}
/**
* Updates block stack and invokes any additional behavior.
*/
@Override
public void enterScope(NodeTraversal t) {
Node n = t.getScopeRoot();
BasicBlock parent = blockStack.isEmpty() ? null : peek(blockStack);
// Don't add all ES6 scope roots to blockStack, only those that are also scopes according to
// the ES5 scoping rules. Other nodes that ought to be considered the root of a BasicBlock
// are added in shouldTraverse() or processScope() and removed in visit().
if (t.isHoistScope()) {
blockStack.add(new BasicBlock(parent, n));
}
}
/**
* Updates block stack and invokes any additional behavior.
*/
@Override
public void exitScope(NodeTraversal t) {
if (t.isHoistScope()) {
pop(blockStack);
}
behavior.afterExitScope(t, new ReferenceMapWrapper(referenceMap));
}
/**
* Updates block stack.
*/
@Override
public boolean shouldTraverse(NodeTraversal nodeTraversal, Node n, Node parent) {
// We automatically traverse a hoisted function body when that function
// is first referenced, so that the reference lists are in the right order.
//
// TODO(nicksantos): Maybe generalize this to a continuation mechanism
// like in RemoveUnusedCode.
if (NodeUtil.isHoistedFunctionDeclaration(n)) {
Node nameNode = n.getFirstChild();
Var functionVar = nodeTraversal.getScope().getVar(nameNode.getString());
checkNotNull(functionVar);
if (finishedFunctionTraverse.contains(functionVar)) {
return false;
}
startedFunctionTraverse.add(functionVar);
}
// If node is a new basic block, put on basic block stack
if (isBlockBoundary(n, parent)) {
blockStack.add(new BasicBlock(peek(blockStack), n));
}
// Add the second x before the first one in "let [x] = x;". VariableReferenceCheck
// relies on reference order to give a warning.
if ((n.isDefaultValue() || n.isDestructuringLhs()) && n.hasTwoChildren()) {
Scope scope = nodeTraversal.getScope();
nodeTraversal.traverseInnerNode(n.getSecondChild(), n, scope);
nodeTraversal.traverseInnerNode(n.getFirstChild(), n, scope);
return false;
}
return true;
}
private static T pop(List list) {
return list.remove(list.size() - 1);
}
private static T peek(List list) {
return Iterables.getLast(list);
}
/**
* @return true if this node marks the start of a new basic block
*/
private static boolean isBlockBoundary(Node n, Node parent) {
if (parent != null) {
switch (parent.getToken()) {
case DO:
case FOR:
case FOR_IN:
case FOR_OF:
case FOR_AWAIT_OF:
case TRY:
case WHILE:
case WITH:
case CLASS:
// NOTE: TRY has up to 3 child blocks:
// TRY
// BLOCK
// BLOCK
// CATCH
// BLOCK
// Note that there is an explicit CATCH token but no explicit
// FINALLY token. For simplicity, we consider each BLOCK
// a separate basic BLOCK.
return true;
case AND:
case HOOK:
case IF:
case OR:
case SWITCH:
case COALESCE:
case OPTCHAIN_GETPROP:
case OPTCHAIN_GETELEM:
case OPTCHAIN_CALL:
// The first child of a conditional is not a boundary,
// but all the rest of the children are.
return n != parent.getFirstChild();
default:
break;
}
}
return n.isCase();
}
private void addReference(Var v, Reference reference) {
// Create collection if none already
ReferenceCollection referenceInfo =
referenceMap.computeIfAbsent(v, k -> new ReferenceCollection());
// Add this particular reference
referenceInfo.add(reference);
}
static class ReferenceMapWrapper implements ReferenceMap {
private final Map referenceMap;
public ReferenceMapWrapper(Map referenceMap) {
this.referenceMap = referenceMap;
}
@Override
public ReferenceCollection getReferences(Var var) {
return referenceMap.get(var);
}
Map getRawReferenceMap() {
return referenceMap;
}
@Override
public String toString() {
return referenceMap.toString();
}
}
/**
* Way for callers to add specific behavior during traversal that
* utilizes the built-up reference information.
*/
public interface Behavior {
/**
* Called after we finish with a scope.
*/
void afterExitScope(NodeTraversal t, ReferenceMap referenceMap);
}
static final Behavior DO_NOTHING_BEHAVIOR = new Behavior() {
@Override
public void afterExitScope(NodeTraversal t, ReferenceMap referenceMap) {}
};
}
