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Closure Compiler is a JavaScript optimizing compiler. It parses your
JavaScript, analyzes it, removes dead code and rewrites and minimizes
what's left. It also checks syntax, variable references, and types, and
warns about common JavaScript pitfalls. It is used in many of Google's
JavaScript apps, including Gmail, Google Web Search, Google Maps, and
Google Docs.
This binary checks for style issues such as incorrect or missing JSDoc
usage, and missing goog.require() statements. It does not do more advanced
checks such as typechecking.
/*
* Copyright 2011 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 com.google.common.base.Preconditions;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.TypeI;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* This pass looks for properties that are never read and removes them.
* These can be properties created using "this", or static properties of
* constructors or interfaces. Explicitly ignored is the possibility that
* these properties may be indirectly referenced using "for-in" or
* "Object.keys". This is the same assumption used with
* RemoveUnusedPrototypeProperties but is slightly wider in scope.
*
* TODO(tomnguyen) Handle destructuring of objects/classes as cases where the field is used.
*
* @author [email protected] (John Lenz)
*/
class RemoveUnusedClassProperties
implements CompilerPass, NodeTraversal.Callback {
private final AbstractCompiler compiler;
private Set used = new HashSet<>();
private List candidates = new ArrayList<>();
private final boolean removeUnusedConstructorProperties;
RemoveUnusedClassProperties(
AbstractCompiler compiler, boolean removeUnusedConstructorProperties) {
this.compiler = compiler;
used.addAll(compiler.getExternProperties());
this.removeUnusedConstructorProperties = removeUnusedConstructorProperties;
}
@Override
public void process(Node externs, Node root) {
NodeTraversal.traverseEs6(compiler, root, this);
removeUnused();
}
private void removeUnused() {
for (Node n : candidates) {
if (NodeUtil.isObjectLitKey(n)) {
String propName = NodeUtil.getObjectLitKeyName(n);
if (!used.contains(propName)) {
// If the property definition has side-effect, finding a place for it
// can be tricky so just leave it in place.
if (!n.isStringKey()
|| !NodeUtil.mayHaveSideEffects(n.getFirstChild(), compiler)) {
Node parent = n.getParent();
parent.removeChild(n);
compiler.reportChangeToEnclosingScope(parent);
}
}
} else {
Preconditions.checkState(n.isGetProp(), n);
String propName = n.getLastChild().getString();
if (!used.contains(propName)) {
Node parent = n.getParent();
Node replacement;
/**
* Whether the parent of the GETPROP is replaced or GETPROP itself.
* In some cases the parent of GETPROP is an EXPRRESULT, while the replacement is always
* just a plain expression.
*/
Boolean replaceParent = true;
if (NodeUtil.isAssignmentOp(parent)) {
Node assign = parent;
Preconditions.checkState(assign != null
&& NodeUtil.isAssignmentOp(assign)
&& assign.getFirstChild() == n);
compiler.reportChangeToEnclosingScope(assign);
// 'this.x = y' to 'y'
replacement = assign.getLastChild().detach();
} else if (parent.isInc() || parent.isDec()) {
compiler.reportChangeToEnclosingScope(parent);
replacement = IR.number(0).srcref(parent);
} else if (parent.isExprResult()) {
replacement = IR.number(0).srcref(n);
replaceParent = false;
} else {
throw new IllegalStateException("unexpected: " + parent);
}
// If the property expression is complex preserve that part of the
// expression.
if (!n.isQualifiedName()) {
Node preserved = n.getFirstChild();
while (preserved.isGetProp()) {
preserved = preserved.getFirstChild();
}
replacement = IR.comma(
preserved.detach(),
replacement)
.srcref(parent);
}
compiler.reportChangeToEnclosingScope(parent);
if (replaceParent) {
parent.replaceWith(replacement);
} else {
parent.replaceChild(n, replacement);
}
}
}
}
}
@Override
public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
return true;
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
switch (n.getToken()) {
case GETPROP: {
String propName = n.getLastChild().getString();
if (compiler.getCodingConvention().isExported(propName)
|| isPinningPropertyUse(n)
|| !isRemovablePropertyDefinition(n)) {
used.add(propName);
} else {
// This is a definition of a property but it is only removable
// if it is defined on "this".
candidates.add(n);
}
break;
}
case OBJECTLIT:
{
// Assume any object literal definition might be a reflection on the
// class property.
if (!NodeUtil.isObjectDefinePropertiesDefinition(n.getParent())) {
for (Node c : n.children()) {
// Object literals can contain computed_prop fields.
if (!c.isComputedProp()) {
used.add(c.getString());
}
}
}
break;
}
case CLASS:
Node classMemberDefs = n.getLastChild();
for (Node m : classMemberDefs.children()) {
// Computed props are treated as unremovable for now.
if (!m.isComputedProp()) {
candidates.add(m);
}
}
break;
case CALL:
// Look for properties referenced through the property rename functions.
Node target = n.getFirstChild();
if (n.hasMoreThanOneChild()
&& compiler
.getCodingConvention()
.isPropertyRenameFunction(target.getOriginalQualifiedName())) {
Node propName = target.getNext();
if (propName.isString()) {
used.add(propName.getString());
}
} else if (NodeUtil.isObjectDefinePropertiesDefinition(n)) {
if (n.getChildCount() == 3 && n.getLastChild().isObjectLit()) {
Node objlit = n.getLastChild();
for (Node c : objlit.children()) {
if (!c.isQuotedString()) {
candidates.add(c);
} else {
used.add(c.getString());
}
}
}
}
break;
default:
break;
}
}
private boolean isRemovablePropertyDefinition(Node n) {
Preconditions.checkState(n.isGetProp(), n);
Node target = n.getFirstChild();
return target.isThis()
|| (this.removeUnusedConstructorProperties && isConstructor(target))
|| (target.isGetProp()
&& target.getLastChild().getString().equals("prototype"));
}
private boolean isConstructor(Node n) {
TypeI type = n.getTypeI();
return type != null && (type.isConstructor() || type.isInterface());
}
/**
* @return Whether the property is used in a way that prevents its removal.
*/
private static boolean isPinningPropertyUse(Node n) {
// Rather than looking for cases that are uses, we assume all references are
// pinning uses unless they are:
// - a simple assignment (x.a = 1)
// - an expression statement (x.a;)
// - a compound assignment or increment (x++, x += 1) whose result is
// otherwise unused
Node parent = n.getParent();
if (n == parent.getFirstChild()) {
if (parent.isAssign() || parent.isExprResult()) {
// A simple assignment or expression statement doesn't pin the property.
return false;
} else if (NodeUtil.isAssignmentOp(parent)
|| parent.isInc() || parent.isDec()) {
// In general, compound assignments are both reads and writes, but
// if the property is never otherwise read we can consider it simply
// a write.
// However if the assign expression is used as part of a larger
// expression, we must consider it a read. For example:
// x = (y.a += 1);
return NodeUtil.isExpressionResultUsed(parent);
}
}
return true;
}
}