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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.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.javascript.jscomp.CodingConvention.SubclassRelationship;
import com.google.javascript.jscomp.ReferenceCollectingCallback.Reference;
import com.google.javascript.jscomp.ReferenceCollectingCallback.ReferenceCollection;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.logging.Logger;
/**
* A {@link Compiler} pass for moving code to a deeper module if possible.
* - currently it only moves functions + variables
*
*/
class CrossModuleCodeMotion implements CompilerPass {
private static final Logger logger =
Logger.getLogger(CrossModuleCodeMotion.class.getName());
private final AbstractCompiler compiler;
private final JSModuleGraph graph;
/**
* Map from module to the node in that module that should parent any string
* variable declarations that have to be moved into that module
*/
private final Map moduleVarParentMap =
new HashMap<>();
/*
* NOTE - I made this a LinkedHashMap to make testing easier. With a regular
* HashMap, the variables may not output in a consistent order
*/
private final Map namedInfo =
new LinkedHashMap<>();
private final Map instanceofNodes =
new LinkedHashMap<>();
private final boolean parentModuleCanSeeSymbolsDeclaredInChildren;
/**
* Creates an instance.
*
* @param compiler The compiler
*/
CrossModuleCodeMotion(
AbstractCompiler compiler,
JSModuleGraph graph,
boolean parentModuleCanSeeSymbolsDeclaredInChildren) {
this.compiler = compiler;
this.graph = graph;
this.parentModuleCanSeeSymbolsDeclaredInChildren =
parentModuleCanSeeSymbolsDeclaredInChildren;
}
@Override
public void process(Node externs, Node root) {
logger.fine("Moving functions + variable into deeper modules");
// If there are <2 modules, then we will never move anything, so we're done
if (graph != null && graph.getModuleCount() > 1) {
// Traverse the tree and find the modules where a var is declared + used
collectReferences(root);
// Make is so we can ignore constructor references in instanceof.
if (parentModuleCanSeeSymbolsDeclaredInChildren) {
makeInstanceOfCodeOrderIndependent();
}
// Move the functions + variables to a deeper module [if possible]
moveCode();
}
}
/** move the code accordingly */
private void moveCode() {
for (NamedInfo info : namedInfo.values()) {
JSModule deepestDependency = info.deepestModule;
// Only move if all are true:
// a) allowMove is true
// b) it was used + declared somewhere [if not, then it will be removed
// as dead or invalid code elsewhere]
// c) the new dependency depends on the declModule
if (info.allowMove && deepestDependency != null) {
Iterator it = info.declarationIterator();
JSModuleGraph moduleGraph = compiler.getModuleGraph();
while (it.hasNext()) {
Declaration decl = it.next();
if (decl.module != null &&
moduleGraph.dependsOn(deepestDependency,
decl.module)) {
// Find the appropriate spot to move it to
Node destParent = moduleVarParentMap.get(deepestDependency);
if (destParent == null) {
destParent = compiler.getNodeForCodeInsertion(deepestDependency);
moduleVarParentMap.put(deepestDependency, destParent);
}
// VAR Nodes are normalized to have only one child.
Node declParent = decl.node.getParent();
Preconditions.checkState(
!declParent.isVar() || declParent.hasOneChild(),
"AST not normalized.");
// Remove it
declParent.detach();
// Add it to the new spot
destParent.addChildToFront(declParent);
compiler.reportCodeChange();
}
}
}
}
}
/** useful information for each variable candidate */
private class NamedInfo {
boolean allowMove = true;
// The deepest module where the variable is used. Starts at null
private JSModule deepestModule = null;
// The module where declarations appear
private JSModule declModule = null;
// information on the spot where the item was declared
private final Deque declarations =
new ArrayDeque<>();
// Add a Module where it is used
void addUsedModule(JSModule m) {
// If we are not allowed to move it, all bets are off
if (!allowMove) {
return;
}
// If we have no deepest module yet, set this one
if (deepestModule == null) {
deepestModule = m;
} else {
// Find the deepest common dependency
deepestModule =
graph.getDeepestCommonDependencyInclusive(m, deepestModule);
}
}
boolean isUsedInOrDependencyOfModule(JSModule m) {
if (deepestModule == null || m == null) {
return false;
}
return m == deepestModule || graph.dependsOn(m, deepestModule);
}
/**
* Add a declaration for this name.
* @return Whether this is a valid declaration. If this returns false,
* this should be added as a reference.
*/
boolean addDeclaration(Declaration d) {
// all declarations must appear in the same module.
if (declModule != null && d.module != declModule) {
return false;
}
declarations.push(d);
declModule = d.module;
return true;
}
/**
* Returns an iterator over the declarations, in the order that they were
* declared.
*/
Iterator declarationIterator() {
return declarations.iterator();
}
}
private static class Declaration {
final JSModule module;
final Node node;
Declaration(JSModule module, Node node) {
this.module = module;
this.node = node;
}
}
/**
* return true if the node has any form of conditional in its ancestry
* TODO(nicksantos) keep track of the conditionals in the ancestry, so
* that we don't have to recrawl it.
*/
private static boolean hasConditionalAncestor(Node n) {
for (Node ancestor : n.getAncestors()) {
switch (ancestor.getToken()) {
case DO:
case FOR:
case FOR_IN:
case HOOK:
case IF:
case SWITCH:
case WHILE:
case FUNCTION:
return true;
default:
break;
}
}
return false;
}
/**
* get the information on a variable
*/
private NamedInfo getNamedInfo(Var v) {
NamedInfo info = namedInfo.get(v);
if (info == null) {
info = new NamedInfo();
namedInfo.put(v, info);
}
return info;
}
/**
* Process the reads to named variables
*/
private void processRead(Reference ref, NamedInfo info) {
// A name is recursively defined if:
// 1: It is calling itself.
// 2: One of its property calls itself.
// Recursive definition should not block movement.
String name = ref.getNode().getString();
boolean recursive = false;
Scope hoistTarget = ref.getScope().getClosestHoistScope();
if (hoistTarget.isFunctionBlockScope()) {
Node rootNode = hoistTarget.getRootNode().getParent();
// CASE #1:
String scopeFuncName = rootNode.getFirstChild().getString();
Node scopeFuncParent = rootNode.getParent();
if (scopeFuncName.equals(name)) {
recursive = true;
} else if (scopeFuncParent.isName() &&
scopeFuncParent.getString().equals(name)) {
recursive = true;
} else {
// CASE #2:
// Suppose name is Foo, we keep look up the scope stack to look for
// a scope with "Foo.prototype.bar = function() { ..... "
for (Scope s = ref.getScope();
s.getParent() != null; s = s.getParent()) {
Node curRoot = s.getRootNode();
if (curRoot.getParent().isAssign()) {
Node owner = curRoot.getParent().getFirstChild();
while (owner.isGetProp()) {
owner = owner.getFirstChild();
}
if (owner.isName() &&
owner.getString().equals(name)) {
recursive = true;
break;
}
}
}
}
}
if (!recursive) {
info.addUsedModule(getModule(ref));
}
}
private void collectReferences(Node root) {
ReferenceCollectingCallback collector = new ReferenceCollectingCallback(
compiler, ReferenceCollectingCallback.DO_NOTHING_BEHAVIOR,
new Es6SyntacticScopeCreator(compiler),
new Predicate() {
@Override public boolean apply(Var var) {
// Only collect global and non-exported names.
return var.isGlobal() && !compiler.getCodingConvention().isExported(var.getName());
}
});
collector.process(root);
for (Var v : collector.getAllSymbols()) {
NamedInfo info = getNamedInfo(v);
if (!info.allowMove) {
continue;
}
ReferenceCollection refCollection = collector.getReferences(v);
for (Reference ref : refCollection) {
processReference(collector, ref, info, v);
}
}
}
private void processReference(
ReferenceCollectingCallback collector, Reference ref, NamedInfo info, Var v) {
Node n = ref.getNode();
if (isRecursiveDeclaration(v, n)) {
return;
}
Node parent = n.getParent();
if (maybeProcessDeclaration(collector, ref, info)) {
// Check to see if the declaration is conditional starting at the
// grandparent of the name node. Since a function declaration
// is considered conditional (the function might not be called)
// we would need to skip the parent in this check as the name could
// just be a function itself.
if (hasConditionalAncestor(parent.getParent())) {
info.allowMove = false;
}
} else {
if (parentModuleCanSeeSymbolsDeclaredInChildren &&
parent.isInstanceOf() && parent.getLastChild() == n) {
instanceofNodes.put(parent, new InstanceofInfo(getModule(ref), info));
} else {
// Otherwise, it's a read
processRead(ref, info);
}
}
}
/**
* @param variable a variable which may be movable
* @param referenceNode a node which is a reference to 'variable'
* @return whether the reference to the variable is a recursive declaration
* e.g. function foo() { foo = function() {}; }
*/
private boolean isRecursiveDeclaration(Var variable, Node referenceNode) {
if (!referenceNode.getParent().isAssign()) {
return false;
}
Node enclosingFunction = NodeUtil.getEnclosingFunction(referenceNode);
return enclosingFunction != null
&& variable.getName().equals(NodeUtil.getNearestFunctionName(enclosingFunction));
}
private JSModule getModule(Reference ref) {
return compiler.getInput(ref.getInputId()).getModule();
}
/**
* Determines whether the given NAME node belongs to a declaration that
* can be moved across modules. If it is, registers it properly.
*
* There are four types of movable declarations:
* 1) var NAME = [movable object];
* 2) function NAME() {}
* 3) NAME = [movable object];
* NAME.prop = [movable object];
* NAME.prop.prop2 = [movable object];
* etc.
* 4) Class-defining function calls, like "inherits" and "mixin".
* NAME.inherits([some other name]);
* where "movable object" is a literal or a function.
*/
private boolean maybeProcessDeclaration(
ReferenceCollectingCallback collector, Reference ref, NamedInfo info) {
Node name = ref.getNode();
Node parent = name.getParent();
Node grandparent = parent.getParent();
switch (parent.getToken()) {
case VAR:
if (canMoveValue(collector, ref.getScope(), name.getFirstChild())) {
return info.addDeclaration(
new Declaration(getModule(ref), name));
}
return false;
case FUNCTION:
if (NodeUtil.isFunctionDeclaration(parent)) {
return info.addDeclaration(
new Declaration(getModule(ref), name));
}
return false;
case ASSIGN:
case GETPROP:
Node child = name;
// Look for assignment expressions where the name is the root
// of a qualified name on the left hand side of the assignment.
for (Node current : name.getAncestors()) {
if (current.isGetProp()) {
// fallthrough
} else if (current.isAssign() &&
current.getFirstChild() == child) {
Node currentParent = current.getParent();
if (currentParent.isExprResult() &&
canMoveValue(
collector, ref.getScope(), current.getLastChild())) {
return info.addDeclaration(
new Declaration(getModule(ref), current));
}
} else {
return false;
}
child = current;
}
return false;
case CALL:
if (NodeUtil.isExprCall(grandparent)) {
SubclassRelationship relationship =
compiler.getCodingConvention().getClassesDefinedByCall(parent);
if (relationship != null &&
name.getString().equals(relationship.subclassName)) {
return info.addDeclaration(
new Declaration(getModule(ref), parent));
}
}
return false;
default:
return false;
}
}
/**
* Determines whether the given value is eligible to be moved across modules.
*/
private static boolean canMoveValue(
ReferenceCollectingCallback collector, Scope scope, Node n) {
// the value is only movable if it's
// a) nothing,
// b) a constant literal,
// c) a function, or
// d) an array/object literal of movable values.
// e) a function stub generated by CrossModuleMethodMotion.
if (n == null || NodeUtil.isLiteralValue(n, true) ||
n.isFunction()) {
return true;
} else if (n.isCall()) {
Node functionName = n.getFirstChild();
return functionName.isName() &&
(functionName.getString().equals(
CrossModuleMethodMotion.STUB_METHOD_NAME) ||
functionName.getString().equals(
CrossModuleMethodMotion.UNSTUB_METHOD_NAME));
} else if (n.isArrayLit() || n.isObjectLit()) {
boolean isObjectLit = n.isObjectLit();
for (Node child = n.getFirstChild(); child != null;
child = child.getNext()) {
if (!canMoveValue(collector, scope,
isObjectLit ? child.getFirstChild() : child)) {
return false;
}
}
return true;
} else if (n.isName()) {
// If the value is guaranteed to never be changed after
// this reference, then we can move it.
Var v = scope.getVar(n.getString());
if (v != null && v.isGlobal()) {
ReferenceCollection refCollection = collector.getReferences(v);
if (refCollection != null &&
refCollection.isWellDefined() &&
refCollection.isAssignedOnceInLifetime()) {
return true;
}
}
}
return false;
}
/**
* Transforms instanceof usages into an expression that short circuits to
* false if tested with a constructor that is undefined. This allows ignoring
* instanceof with respect to cross module code motion.
*/
private void makeInstanceOfCodeOrderIndependent() {
Node tmp = IR.block();
for (Map.Entry entry : instanceofNodes.entrySet()) {
Node n = entry.getKey();
InstanceofInfo info = entry.getValue();
if (!info.namedInfo.allowMove || !info.mustBeGuardedByTypeof()) {
continue;
}
// In order for the compiler pass to be idempotent, this checks whether
// the instanceof is already wrapped in the code that is generated below.
Node parent = n.getParent();
if (parent.isAnd() && parent.getLastChild() == n
&& parent.getFirstChild().isNE()) {
Node ne = parent.getFirstChild();
if (ne.getFirstChild().isString()
&& "undefined".equals(ne.getFirstChild().getString())
&& ne.getLastChild().isTypeOf()) {
Node ref = ne.getLastChild().getFirstChild();
if (ref.isEquivalentTo(n.getLastChild())) {
continue;
}
}
}
// Wrap "foo instanceof Bar" in
// "('undefined' != typeof Bar && foo instanceof Bar)"
Node reference = n.getLastChild().cloneNode();
Preconditions.checkState(reference.isName());
n.replaceWith(tmp);
Node and = IR.and(
new Node(Token.NE,
IR.string("undefined"),
new Node(Token.TYPEOF, reference)
),
n
);
and.useSourceInfoIfMissingFromForTree(n);
tmp.replaceWith(and);
compiler.reportCodeChange();
}
}
private static class InstanceofInfo {
private final JSModule module;
private final NamedInfo namedInfo;
InstanceofInfo(JSModule module, NamedInfo namedInfo) {
this.module = module;
this.namedInfo = namedInfo;
}
/**
* Returns true if this instance of instanceof is in a deeper module than
* the deepest module (by reference) of the related name.
* In that case the name may be undefined when the instanceof runs and we
* have to guard it with typeof.
*/
boolean mustBeGuardedByTypeof() {
return !this.namedInfo.isUsedInOrDependencyOfModule(this.module);
}
}
}