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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 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 static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Supplier;
import com.google.common.collect.Lists;
import com.google.javascript.jscomp.ReferenceCollectingCallback.Behavior;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import com.google.javascript.rhino.TokenStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Using the infrastructure provided by {@link ReferenceCollectingCallback},
* identify variables that are only ever assigned to object literals
* and that are never used in entirety, and expand the objects into
* individual variables.
*
* Based on the InlineVariables pass
*/
class InlineObjectLiterals implements CompilerPass {
public static final String VAR_PREFIX = "JSCompiler_object_inline_";
public static final String STRING_KEY_IDENTIFIER = "string_key";
private final AbstractCompiler compiler;
private final Supplier safeNameIdSupplier;
InlineObjectLiterals(
AbstractCompiler compiler,
Supplier safeNameIdSupplier) {
this.compiler = compiler;
this.safeNameIdSupplier = safeNameIdSupplier;
}
@Override
public void process(Node externs, Node root) {
ReferenceCollectingCallback callback =
new ReferenceCollectingCallback(
compiler, new InliningBehavior(), new SyntacticScopeCreator(compiler));
callback.process(externs, root);
}
/**
* Builds up information about nodes in each scope. When exiting the
* scope, inspects all variables in that scope, and inlines any
* that we can.
*/
private class InliningBehavior implements Behavior {
/**
* A list of variables that should not be inlined, because their
* reference information is out of sync with the state of the AST.
*/
private final Set staleVars = new HashSet<>();
@Override
public void afterExitScope(NodeTraversal t, ReferenceMap referenceMap) {
for (Var v : t.getScope().getVarIterable()) {
if (isVarInlineForbidden(v)) {
continue;
}
ReferenceCollection referenceInfo = referenceMap.getReferences(v);
if (isInlinableObject(referenceInfo.references)) {
// Blacklist the object itself, as well as any other values
// that it refers to, since they will have been moved around.
staleVars.add(v);
Reference init = referenceInfo.getInitializingReference();
// Split up the object into individual variables if the object
// is never referenced directly in full.
splitObject(v, init, referenceInfo);
}
}
}
/**
* If there are any variable references in the given node tree,
* blacklist them to prevent the pass from trying to inline the
* variable. Any code modifications will have potentially made the
* ReferenceCollection invalid.
*/
private void blacklistVarReferencesInTree(Node root, final Scope scope) {
NodeUtil.visitPreOrder(root, new NodeUtil.Visitor() {
@Override
public void visit(Node node) {
if (node.isName()) {
staleVars.add(scope.getVar(node.getString()));
}
}
}, NodeUtil.MATCH_NOT_FUNCTION);
}
/**
* Whether the given variable is forbidden from being inlined.
*/
private boolean isVarInlineForbidden(Var var) {
// A variable may not be inlined if:
// 1) The variable is defined in the externs
// 2) The variable is exported,
// 3) Don't inline the special RENAME_PROPERTY_FUNCTION_NAME
// 4) A reference to the variable has been inlined. We're downstream
// of the mechanism that creates variable references, so we don't
// have a good way to update the reference. Just punt on it.
// Additionally, exclude global variables for now.
return var.isGlobal()
|| var.isExtern()
|| compiler.getCodingConvention().isExported(var.getName())
|| compiler
.getCodingConvention()
.isPropertyRenameFunction(var.getNameNode().getQualifiedName())
|| staleVars.contains(var);
}
/**
* Counts the number of direct (full) references to an object.
* Specifically, we check for references of the following type:
*
* x;
* x.fn();
*
*/
private boolean isInlinableObject(List refs) {
boolean ret = false;
Set validProperties = new HashSet<>();
for (Reference ref : refs) {
Node name = ref.getNode();
Node parent = ref.getParent();
Node grandparent = ref.getGrandparent();
// Ignore most indirect references, like x.y (but not x.y(),
// since the function referenced by y might reference 'this').
//
if (parent.isGetProp()) {
checkState(parent.getFirstChild() == name);
// A call target may be using the object as a 'this' value.
if (grandparent.isCall()
&& grandparent.getFirstChild() == parent) {
return false;
}
// Deleting a property has different semantics from deleting
// a variable, so deleted properties should not be inlined.
if (grandparent.isDelProp()) {
return false;
}
// NOTE(nicksantos): This pass's object-splitting algorithm has
// a blind spot. It assumes that if a property isn't defined on an
// object, then the value is undefined. This is not true, because
// Object.prototype can have arbitrary properties on it.
//
// We short-circuit this problem by bailing out if we see a reference
// to a property that isn't defined on the object literal. This
// isn't a perfect algorithm, but it should catch most cases.
String propName = parent.getLastChild().getString();
if (!validProperties.contains(propName)) {
if (NodeUtil.isNameDeclOrSimpleAssignLhs(parent, grandparent)) {
validProperties.add(propName);
} else {
return false;
}
}
continue;
}
// Only rewrite VAR declarations or simple assignment statements
if (!isVarOrAssignExprLhs(name)) {
return false;
}
// Don't try to handle rewriting VAR/CONST/LET declarations inside for loops.
// Currently, normalization moves var declarations out of for loop initializers anyway.
// let/const are more difficult. Declaring each property outside the for loop puts them
// in an incorrect scope. Declaring them in the loop would initialize them multiple times.
if (NodeUtil.isNameDeclaration(parent) && NodeUtil.isAnyFor(grandparent)) {
return false;
}
Node val = ref.getAssignedValue();
if (val == null) {
// A var with no assignment.
continue;
}
// We're looking for object literal assignments only.
if (!val.isObjectLit()) {
return false;
}
// Make sure that the value is not self-referential. IOW,
// disallow things like x = {b: x.a}.
//
// TODO(dimvar): Only exclude unorderable self-referential
// assignments. i.e. x = {a: x.b, b: x.a} is not orderable,
// but x = {a: 1, b: x.a} is.
//
// Also, ES5 getters/setters aren't handled by this pass.
for (Node child = val.getFirstChild(); child != null;
child = child.getNext()) {
switch (child.getToken()) {
// ES5 get/set not supported.
case GETTER_DEF:
case SETTER_DEF:
// Don't inline computed property names
case COMPUTED_PROP:
// Spread can overwrite any preceding prop if there are matching keys.
// TODO(b/126567617): Allow inlining props declared after the SPREAD.
case OBJECT_SPREAD:
return false;
case MEMBER_FUNCTION_DEF:
case STRING_KEY:
break;
default:
throw new IllegalStateException(
"Unexpected child of OBJECTLIT: " + child.toStringTree());
}
validProperties.add(child.getString());
Node childVal = child.getFirstChild();
// Check if childVal is the parent of any of the passed in
// references, as that is how self-referential assignments
// will happen.
for (Reference t : refs) {
Node refNode = t.getParent();
while (!NodeUtil.isStatementBlock(refNode)) {
if (refNode == childVal) {
// There's a self-referential assignment
return false;
}
refNode = refNode.getParent();
}
}
}
// We have found an acceptable object literal assignment. As
// long as there are no other assignments that mess things up,
// we can inline.
ret = true;
}
return ret;
}
private boolean isVarOrAssignExprLhs(Node n) {
Node parent = n.getParent();
return NodeUtil.isNameDeclaration(parent)
|| (parent.isAssign()
&& parent.getFirstChild() == n
&& parent.getParent().isExprResult());
}
/**
* Computes a list of ever-referenced keys in the object being
* inlined, and returns a mapping of key name -> generated
* variable name.
*/
private Map computeVarList(
ReferenceCollection referenceInfo) {
Map varmap = new LinkedHashMap<>();
for (Reference ref : referenceInfo.references) {
if (ref.isLvalue() || ref.isInitializingDeclaration()) {
Node val = ref.getAssignedValue();
if (val != null) {
checkState(val.isObjectLit(), val);
for (Node child = val.getFirstChild(); child != null;
child = child.getNext()) {
String varname = child.getString();
if (varmap.containsKey(varname)) {
continue;
}
String var = varname;
if (!TokenStream.isJSIdentifier(varname)) {
var = STRING_KEY_IDENTIFIER;
}
var = VAR_PREFIX + var + "_" + safeNameIdSupplier.get();
varmap.put(varname, var);
}
}
} else if (NodeUtil.isNameDeclaration(ref.getParent())) {
// This is the var. There is no value.
} else {
Node getprop = ref.getParent();
checkState(getprop.isGetProp(), getprop);
// The key being looked up in the original map.
String varname = getprop.getLastChild().getString();
if (varmap.containsKey(varname)) {
continue;
}
String var = VAR_PREFIX + varname + "_" + safeNameIdSupplier.get();
varmap.put(varname, var);
}
}
return varmap;
}
/**
* Populates a map of key names -> initial assigned values. The
* object literal these are being pulled from is invalidated as
* a result.
*/
private void fillInitialValues(Reference init, Map initvals) {
Node object = init.getAssignedValue();
checkState(object.isObjectLit(), object);
for (Node key = object.getFirstChild(); key != null;
key = key.getNext()) {
initvals.put(key.getString(), key.removeFirstChild());
}
}
/**
* Replaces an assignment like x = {...} with t1=a,t2=b,t3=c,true.
* Note that the resulting expression will always evaluate to
* true, as would the x = {...} expression.
*/
private void replaceAssignmentExpression(Var v, Reference ref,
Map varmap) {
// Compute all of the assignments necessary
List nodes = new ArrayList<>();
Node val = ref.getAssignedValue();
blacklistVarReferencesInTree(val, v.getScope());
checkState(val.isObjectLit(), val);
Set all = new LinkedHashSet<>(varmap.keySet());
for (Node key = val.getFirstChild(); key != null;
key = key.getNext()) {
String var = key.getString();
Node value = key.removeFirstChild();
// TODO(user): Copy type information.
nodes.add(
IR.assign(
IR.name(varmap.get(var)),
value));
all.remove(var);
}
// TODO(user): Better source information.
for (String var : all) {
nodes.add(
IR.assign(
IR.name(varmap.get(var)),
NodeUtil.newUndefinedNode(null)));
}
Node replacement;
if (nodes.isEmpty()) {
replacement = IR.trueNode();
} else {
// All assignments evaluate to true, so make sure that the
// expr statement evaluates to true in case it matters.
nodes.add(IR.trueNode());
// Join these using COMMA. A COMMA node must have 2 children, so we
// create a tree. In the tree the first child be the COMMA to match
// the parser, otherwise tree equality tests fail.
nodes = Lists.reverse(nodes);
replacement = new Node(Token.COMMA);
Node cur = replacement;
int i;
for (i = 0; i < nodes.size() - 2; i++) {
cur.addChildToFront(nodes.get(i));
Node t = new Node(Token.COMMA);
cur.addChildToFront(t);
cur = t;
}
cur.addChildToFront(nodes.get(i));
cur.addChildToFront(nodes.get(i + 1));
}
Node replace = ref.getParent();
replacement.useSourceInfoIfMissingFromForTree(replace);
if (NodeUtil.isNameDeclaration(replace)) {
replace.replaceWith(NodeUtil.newExpr(replacement));
} else {
replace.replaceWith(replacement);
}
}
/**
* Splits up the object literal into individual variables, and
* updates all uses.
*/
private void splitObject(Var v, Reference init,
ReferenceCollection referenceInfo) {
// First figure out the FULL set of possible keys, so that they
// can all be properly set as necessary.
Map varmap = computeVarList(referenceInfo);
Map initvals = new HashMap<>();
// Figure out the top-level of the var assign node. If it's a plain
// ASSIGN, then there's an EXPR_STATEMENT above it, if it's a
// VAR then it should be directly replaced.
Node vnode;
boolean defined =
referenceInfo.isWellDefined() && NodeUtil.isNameDeclaration(init.getParent());
if (defined) {
vnode = init.getParent();
fillInitialValues(init, initvals);
} else {
// Find the beginning of the function body / script.
vnode = v.getScope().getClosestHoistScope().getRootNode().getFirstChild();
}
checkState(NodeUtil.isStatement(vnode), vnode);
for (Map.Entry entry : varmap.entrySet()) {
Node val = initvals.get(entry.getKey());
Node newVarNode = NodeUtil.newVarNode(entry.getValue(), val);
if (val == null) {
// is this right?
newVarNode.useSourceInfoIfMissingFromForTree(vnode);
} else {
blacklistVarReferencesInTree(val, v.getScope());
}
vnode.getParent().addChildBefore(newVarNode, vnode);
compiler.reportChangeToEnclosingScope(vnode);
}
if (defined) {
compiler.reportChangeToEnclosingScope(vnode.getParent());
vnode.detach();
}
for (Reference ref : referenceInfo.references) {
// The init/decl have already been converted.
if (defined && ref == init) {
continue;
}
compiler.reportChangeToEnclosingScope(ref.getNode());
if (ref.isLvalue()) {
// Assignments have to be handled specially, since they
// expand out into multiple assignments.
replaceAssignmentExpression(v, ref, varmap);
} else if (NodeUtil.isNameDeclaration(ref.getParent())) {
// The old variable declaration. It didn't have a
// value. Remove it entirely as it should now be unused.
ref.getGrandparent().removeChild(ref.getParent());
} else {
// Make sure that the reference is a GETPROP as we expect it to be.
Node getprop = ref.getParent();
checkState(getprop.isGetProp(), getprop);
// The key being looked up in the original map.
String var = getprop.getSecondChild().getString();
// If the variable hasn't already been declared, add an empty
// declaration near all the other declarations.
checkState(varmap.containsKey(var));
// Replace the GETPROP node with a NAME.
Node replacement = IR.name(varmap.get(var));
replacement.useSourceInfoIfMissingFrom(getprop);
ref.getGrandparent().replaceChild(ref.getParent(), replacement);
}
}
}
}
}