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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.
/*
* 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 com.google.javascript.jscomp.CodingConvention.AssertionFunctionLookup;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.Node;
import java.util.ArrayList;
import java.util.List;
/**
* Compiler pass that removes Closure-specific code patterns.
*
* Currently does the following:
*
*
* - Instead of setting abstract methods to a function that throws an
* informative error, this pass allows some binary size reduction by
* removing these methods altogether for production builds.
* - Remove calls to assertion functions (like goog.asserts.assert).
* If the return value of the assertion function is used, then
* the first argument (the asserted value) will be directly inlined.
* Otherwise, the entire call will be removed. It is well-known that
* this is not provably safe, much like the equivalent assert
* statement in Java.
*
*/
final class ClosureCodeRemoval implements CompilerPass {
/** Reference to the JS compiler */
private final AbstractCompiler compiler;
/** Name used to denote an abstract function */
static final String ABSTRACT_METHOD_NAME = "goog.abstractMethod";
private final boolean removeAbstractMethods;
private final boolean removeAssertionCalls;
/**
* List of names referenced in successive generations of finding referenced
* nodes.
*/
private final List abstractMethodAssignmentNodes =
new ArrayList<>();
/** List of member function definition nodes annotated with @abstract. */
private final List abstractMemberFunctionNodes = new ArrayList<>();
/**
* List of assertion functions.
*/
private final List assertionCalls = new ArrayList<>();
/**
* Utility class to track a node and its parent.
*/
private class RemovableAssignment {
/**
* The node
*/
final Node node;
/**
* Its parent
*/
final Node parent;
/**
* Full chain of ASSIGN ancestors
*/
final List assignAncestors = new ArrayList<>();
/**
* The last ancestor
*/
final Node lastAncestor;
/**
* Data structure for information about a removable assignment.
*
* @param nameNode The LHS
* @param assignNode The parent ASSIGN node
* @param traversal Access to further levels, assumed to start at 1
*/
public RemovableAssignment(Node nameNode, Node assignNode,
NodeTraversal traversal) {
this.node = nameNode;
this.parent = assignNode;
Node ancestor = assignNode;
do {
ancestor = ancestor.getParent();
assignAncestors.add(ancestor);
} while (ancestor.isAssign() &&
ancestor.getFirstChild().isQualifiedName());
lastAncestor = ancestor.getParent();
}
/**
* Remove this node.
*/
public void remove() {
Node rhs = node.getNext();
Node last = parent;
for (Node ancestor : assignAncestors) {
if (ancestor.isExprResult()) {
ancestor.detach();
NodeUtil.markFunctionsDeleted(ancestor, compiler);
} else {
rhs.detach();
last.replaceWith(rhs);
}
last = ancestor;
}
compiler.reportChangeToEnclosingScope(lastAncestor);
}
}
/**
* Identifies all assignments of the abstract method to a variable and all methods annotated with
* "@abstract" in their JSDoc.
*/
private class FindAbstractMethods extends AbstractPostOrderCallback {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isAssign()) {
Node nameNode = n.getFirstChild();
Node valueNode = n.getLastChild();
if (nameNode.isQualifiedName() &&
valueNode.isQualifiedName() &&
valueNode.matchesQualifiedName(ABSTRACT_METHOD_NAME)) {
// Foo.prototype.bar = goog.abstractMethod
abstractMethodAssignmentNodes.add(
new RemovableAssignment(n.getFirstChild(), n, t));
} else if (n.getJSDocInfo() != null
&& n.getJSDocInfo().isAbstract()
&& NodeUtil.isEmptyFunctionExpression(valueNode)
&& !n.getJSDocInfo().isConstructor()) {
// @abstract
abstractMethodAssignmentNodes.add(
new RemovableAssignment(n.getFirstChild(), n, t));
}
} else if (n.isMemberFunctionDef() && parent.isClassMembers()) {
if (n.getJSDocInfo() != null && n.getJSDocInfo().isAbstract()) {
abstractMemberFunctionNodes.add(n);
}
}
}
}
/**
* Identifies all assertion calls.
*/
private class FindAssertionCalls extends AbstractPostOrderCallback {
final AssertionFunctionLookup assertionNames;
FindAssertionCalls() {
assertionNames =
AssertionFunctionLookup.of(compiler.getCodingConvention().getAssertionFunctions());
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (!n.isCall()) {
return;
}
Node callee = n.getFirstChild();
if (assertionNames.lookupByCallee(callee) != null // type-based
|| (callee.getColor() != null && callee.getColor().isClosureAssert())) { // color-based
assertionCalls.add(n);
}
}
}
/**
* Creates a Closure code remover.
*
* @param compiler The AbstractCompiler
* @param removeAbstractMethods Remove declarations of abstract methods.
* @param removeAssertionCalls Remove calls to goog.assert functions.
*/
ClosureCodeRemoval(AbstractCompiler compiler, boolean removeAbstractMethods,
boolean removeAssertionCalls) {
this.compiler = compiler;
this.removeAbstractMethods = removeAbstractMethods;
this.removeAssertionCalls = removeAssertionCalls;
}
@Override
public void process(Node externs, Node root) {
List passes = new ArrayList<>();
if (removeAbstractMethods) {
passes.add(new FindAbstractMethods());
}
if (removeAssertionCalls) {
passes.add(new FindAssertionCalls());
}
CombinedCompilerPass.traverse(compiler, root, passes);
for (RemovableAssignment assignment : abstractMethodAssignmentNodes) {
assignment.remove();
}
for (Node memberFunction : abstractMemberFunctionNodes) {
compiler.reportFunctionDeleted(memberFunction.getFirstChild());
Node parent = memberFunction.getParent();
memberFunction.detach();
compiler.reportChangeToEnclosingScope(parent);
}
for (Node call : assertionCalls) {
// If the assertion is an expression, just strip the whole thing.
compiler.reportChangeToEnclosingScope(call);
Node parent = call.getParent();
if (parent.isExprResult()) {
parent.detach();
NodeUtil.markFunctionsDeleted(parent, compiler);
} else {
// Otherwise, replace the assertion with its first argument,
// which is the return value of the assertion.
Node firstArg = call.getSecondChild();
if (firstArg == null) {
call.replaceWith(NodeUtil.newUndefinedNode(call));
} else {
Node replacement = firstArg.detach();
replacement.copyTypeFrom(call);
call.replaceWith(replacement);
}
NodeUtil.markFunctionsDeleted(call, compiler);
}
}
}
}