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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.
The newest version!
/*
* Copyright 2007 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.SubclassRelationship;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.HashSet;
import java.util.Set;
import javax.annotation.Nullable;
/**
* A pass for stripping a list of provided JavaScript object types.
*
* The stripping strategy is as follows:
* - Provide: 1) a list of types that should be stripped, and 2) a list of
* suffixes of field/variable names that should be stripped.
* - Remove declarations of variables that are initialized using static
* methods of strip types (e.g. var x = goog.debug.Logger.getLogger(...);).
* - Remove all references to variables that are stripped.
* - Remove all object literal keys with strip names.
* - Remove all assignments to 1) field names that are strip names and
* 2) qualified names that begin with strip types.
* - Remove all statements containing calls to static methods of strip types.
*
*/
class StripCode implements CompilerPass {
// TODO(user): Try eliminating the need for a list of strip names by instead
// recording which field names are assigned to debug types in each JS input.
private final AbstractCompiler compiler;
private final Set stripTypes;
private final Set stripNameSuffixes;
private final Set stripTypePrefixes;
private final Set stripNamePrefixes;
private final Set varsToRemove;
static final DiagnosticType STRIP_TYPE_INHERIT_ERROR = DiagnosticType.error(
"JSC_STRIP_TYPE_INHERIT_ERROR",
"Non-strip type {0} cannot inherit from strip type {1}");
static final DiagnosticType STRIP_ASSIGNMENT_ERROR = DiagnosticType.error(
"JSC_STRIP_ASSIGNMENT_ERROR",
"Unable to strip assignment to {0}");
/**
* Creates an instance.
*
* @param compiler The compiler
*/
StripCode(AbstractCompiler compiler,
Set stripTypes,
Set stripNameSuffixes,
Set stripTypePrefixes,
Set stripNamePrefixes) {
this.compiler = compiler;
this.stripTypes = new HashSet<>(stripTypes);
this.stripNameSuffixes = new HashSet<>(stripNameSuffixes);
this.stripTypePrefixes = new HashSet<>(stripTypePrefixes);
this.stripNamePrefixes = new HashSet<>(stripNamePrefixes);
this.varsToRemove = new HashSet<>();
}
/**
* Enables stripping of goog.tweak functions.
*/
public void enableTweakStripping() {
stripTypes.add("goog.tweak");
}
@Override
public void process(Node externs, Node root) {
// Always strip types that defined on a type that is being stripped, otherwise the
// resulting code will be invalid, so add "prefix" stripping that isn't a partial name.
// TODO(johnlenz): I'm not sure what the original intent of "type prefix" stripping was.
// Verify that we can always assume a complete namespace and simplify this logic.
for (String type : stripTypes) {
stripTypePrefixes.add(type + ".");
}
NodeTraversal.traverse(compiler, root, new Strip());
// This pass may remove definitions of getter or setter properties
GatherGettersAndSetterProperties.update(compiler, externs, root);
}
// -------------------------------------------------------------------------
/**
* A callback that strips debug code from a JavaScript parse tree.
*/
private class Strip extends AbstractPostOrderCallback {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
switch (n.getToken()) {
case VAR:
case CONST:
case LET:
removeVarDeclarationsByNameOrRvalue(t, n, parent);
break;
case NAME:
maybeRemoveReferenceToRemovedVariable(t, n, parent);
break;
case ASSIGN:
case ASSIGN_BITOR:
case ASSIGN_BITXOR:
case ASSIGN_BITAND:
case ASSIGN_LSH:
case ASSIGN_RSH:
case ASSIGN_URSH:
case ASSIGN_ADD:
case ASSIGN_SUB:
case ASSIGN_MUL:
case ASSIGN_DIV:
case ASSIGN_MOD:
maybeEliminateAssignmentByLvalueName(t, n, parent);
break;
case CALL:
case NEW:
maybeRemoveCall(t, n, parent);
break;
case OBJECTLIT:
eliminateKeysWithStripNamesFromObjLit(t, n);
break;
case EXPR_RESULT:
maybeEliminateExpressionByName(t, n, parent);
break;
case CLASS:
maybeEliminateClassByNameOrExtends(t, n, parent);
break;
default:
break;
}
}
/**
* Removes declarations of any variables whose names are strip names or whose whose r-values are
* static method calls on strip types. Builds a set of removed variables so that all references
* to them can be removed.
*
* @param t The traversal
* @param n A VAR, CONST, or LET node
* @param parent {@code n}'s parent
*/
void removeVarDeclarationsByNameOrRvalue(NodeTraversal t, Node n, Node parent) {
Node next = null;
for (Node nameNode = n.getFirstChild(); nameNode != null; nameNode = next) {
next = nameNode.getNext();
if (nameNode.isDestructuringLhs()) {
continue;
}
String name = nameNode.getString();
if (isStripName(name)
|| isCallWhoseReturnValueShouldBeStripped(nameNode.getFirstChild())) {
// Remove the NAME.
Scope scope = t.getScope();
varsToRemove.add(scope.getVar(name));
n.removeChild(nameNode);
NodeUtil.markFunctionsDeleted(nameNode, compiler);
}
}
if (!n.hasChildren()) {
// Must also remove the VAR.
replaceWithEmpty(n, parent);
t.reportCodeChange();
}
}
/**
* Removes a reference if it is a reference to a removed variable.
*
* @param t The traversal
* @param n A NAME node
* @param parent {@code n}'s parent
*/
void maybeRemoveReferenceToRemovedVariable(NodeTraversal t, Node n,
Node parent) {
switch (parent.getToken()) {
case VAR:
case CONST:
case LET:
// This is a variable declaration, not a reference.
break;
case GETPROP:
// GETPROP
// NAME
// STRING (property name)
case GETELEM:
// GETELEM
// NAME
// NUMBER|STRING|NAME|...
if (parent.getFirstChild() == n && isReferenceToRemovedVar(t, n)) {
replaceHighestNestedCallWithNull(t, parent, parent.getParent());
}
break;
case ASSIGN:
case ASSIGN_BITOR:
case ASSIGN_BITXOR:
case ASSIGN_BITAND:
case ASSIGN_LSH:
case ASSIGN_RSH:
case ASSIGN_URSH:
case ASSIGN_ADD:
case ASSIGN_SUB:
case ASSIGN_MUL:
case ASSIGN_DIV:
case ASSIGN_MOD:
if (isReferenceToRemovedVar(t, n)) {
if (parent.getFirstChild() == n) {
Node grandparent = parent.getParent();
if (grandparent.isExprResult()) {
// Remove the assignment.
Node greatGrandparent = grandparent.getParent();
replaceWithEmpty(grandparent, greatGrandparent);
t.reportCodeChange();
} else {
// Substitute the r-value for the assignment.
Node rvalue = n.getNext();
parent.removeChild(rvalue);
grandparent.replaceChild(parent, rvalue);
t.reportCodeChange();
}
} else {
// The var reference is the r-value. Replace it with null.
replaceWithNull(n, parent);
t.reportCodeChange();
}
}
break;
default:
if (isReferenceToRemovedVar(t, n)) {
replaceWithNull(n, parent);
t.reportCodeChange();
}
break;
}
}
/**
* Use a while loop to get up out of any nested calls. For example,
* if we have just detected that we need to remove the a.b() call
* in a.b().c().d(), we'll have to remove all of the calls, and it
* will take a few iterations through this loop to get up to d().
*/
void replaceHighestNestedCallWithNull(NodeTraversal t, Node node, Node parent) {
Node ancestor = parent;
Node ancestorChild = node;
Node ancestorParent;
while (true) {
ancestorParent = ancestor.getParent();
if (ancestor.getFirstChild() != ancestorChild) {
replaceWithNull(ancestorChild, ancestor);
break;
}
if (ancestor.isExprResult()) {
// Remove the entire expression statement.
replaceWithEmpty(ancestor, ancestorParent);
break;
}
if (ancestor.isAssign()) {
ancestorParent.replaceChild(ancestor, ancestor.getLastChild().detach());
break;
}
if (!NodeUtil.isGet(ancestor)
&& !ancestor.isCall()) {
replaceWithNull(ancestorChild, ancestor);
break;
}
// Is not executed on the last iteration so can't be used for change reporting.
ancestorChild = ancestor;
ancestor = ancestorParent;
}
t.reportCodeChange();
}
/**
* Eliminates an assignment if the l-value is:
* - A field name that's a strip name
* - A qualified name that begins with a strip type
*
* @param t The traversal
* @param n An ASSIGN node
* @param parent {@code n}'s parent
*/
void maybeEliminateAssignmentByLvalueName(NodeTraversal t, Node n,
Node parent) {
// ASSIGN
// l-value
// r-value
Node lvalue = n.getFirstChild();
if (nameIncludesFieldNameToStrip(lvalue) ||
qualifiedNameBeginsWithStripType(lvalue)) {
// Limit to EXPR_RESULT because it is not
// safe to eliminate assignment in complex expressions,
// e.g. in ((x = 7) + 8)
if (parent.isExprResult()) {
Node grandparent = parent.getParent();
replaceWithEmpty(parent, grandparent);
compiler.reportChangeToEnclosingScope(grandparent);
} else {
t.report(n, STRIP_ASSIGNMENT_ERROR, lvalue.getQualifiedName());
}
}
}
/**
* Eliminates an expression if it refers to:
* - A field name that's a strip name
* - A qualified name that begins with a strip type
* This gets rid of construct like:
* a.prototype.logger; (used instead of a.prototype.logger = null;)
* This expression is not an assignment and so will not be caught by
* maybeEliminateAssignmentByLvalueName.
* @param t The traversal
* @param n An EXPR_RESULT node
* @param parent {@code n}'s parent
*/
void maybeEliminateExpressionByName(NodeTraversal t, Node n,
Node parent) {
// EXPR_RESULT
// expression
Node expression = n.getFirstChild();
if (nameIncludesFieldNameToStrip(expression) ||
qualifiedNameBeginsWithStripType(expression)) {
if (parent.isExprResult()) {
Node grandparent = parent.getParent();
replaceWithEmpty(parent, grandparent);
compiler.reportChangeToEnclosingScope(grandparent);
} else {
replaceWithEmpty(n, parent);
compiler.reportChangeToEnclosingScope(parent);
}
}
}
/**
* Removes a method call if {@link #isMethodOrCtorCallThatTriggersRemoval}
* indicates that it should be removed.
*
* @param t The traversal
* @param n A CALL node
* @param parent {@code n}'s parent
*/
void maybeRemoveCall(NodeTraversal t, Node n, Node parent) {
// CALL/NEW
// function
// arguments
if (isMethodOrCtorCallThatTriggersRemoval(t, n, parent)) {
replaceHighestNestedCallWithNull(t, n, parent);
}
}
/**
* Eliminates any object literal keys in an object literal declaration that
* have strip names.
*
* @param t The traversal
* @param n An OBJLIT node
*/
void eliminateKeysWithStripNamesFromObjLit(NodeTraversal t, Node n) {
// OBJLIT
// key1
// value1
// key2
// ...
Node key = n.getFirstChild();
while (key != null) {
switch (key.getToken()) {
case GETTER_DEF:
case SETTER_DEF:
case STRING_KEY:
case MEMBER_FUNCTION_DEF:
if (isStripName(key.getString())) {
Node next = key.getNext();
n.removeChild(key);
NodeUtil.markFunctionsDeleted(key, compiler);
key = next;
compiler.reportChangeToEnclosingScope(n);
break;
}
// fall through
default:
key = key.getNext();
}
}
}
/**
* Removes a class definition if the name is a strip type. Warns if a non-strippable class
* is extending a strippable type.
*/
void maybeEliminateClassByNameOrExtends(NodeTraversal t, Node classNode, Node parent) {
Node nameNode = NodeUtil.getNameNode(classNode);
String className = "";
// Replace class with null if it is a strip type
if (nameNode != null && nameNode.isQualifiedName()) {
className = nameNode.getQualifiedName();
if (qualifiedNameBeginsWithStripType(className)) {
if (NodeUtil.isStatementParent(parent)) {
replaceWithEmpty(classNode, parent);
} else {
replaceWithNull(classNode, parent);
}
t.reportCodeChange();
return;
}
}
// If the class is not a strip type, the superclass also cannot be a strip type
Node superclassNode = classNode.getSecondChild();
if (superclassNode != null && superclassNode.isQualifiedName()) {
String superclassName = superclassNode.getQualifiedName();
if (qualifiedNameBeginsWithStripType(superclassName)) {
t.report(classNode, STRIP_TYPE_INHERIT_ERROR, className, superclassName);
}
}
}
/**
* Gets whether a node is a CALL node whose return value should be
* stripped. A call's return value should be stripped if the function
* getting called is a static method in a class that gets stripped. For
* example, if "goog.debug.Logger" is a strip name, then this function
* returns true for a call such as "goog.debug.Logger.getLogger(...)". It
* may also simply be a function that is getting stripped. For example,
* if "getLogger" is a strip name, but not "goog.debug.Logger", this will
* still return true.
*
* @param n A node (typically a CALL node)
* @return Whether the call's return value should be stripped
*/
boolean isCallWhoseReturnValueShouldBeStripped(@Nullable Node n) {
return n != null &&
(n.isCall() ||
n.isNew()) &&
n.hasChildren() &&
(qualifiedNameBeginsWithStripType(n.getFirstChild()) ||
nameIncludesFieldNameToStrip(n.getFirstChild()));
}
/**
* Gets whether a qualified name begins with a strip name. The names
* "goog.debug", "goog.debug.Logger", and "goog.debug.Logger.Level" are
* examples of strip names that would result in this function returning
* true for a node representing the name "goog.debug.Logger.Level".
*
* @param n A node (typically a NAME or GETPROP node)
* @return Whether the name begins with a strip name
*/
boolean qualifiedNameBeginsWithStripType(Node n) {
String name = n.getQualifiedName();
return qualifiedNameBeginsWithStripType(name);
}
/**
* Gets whether a qualified name begins with a strip name. The names
* "goog.debug", "goog.debug.Logger", and "goog.debug.Logger.Level" are
* examples of strip names that would result in this function returning
* true for a node representing the name "goog.debug.Logger.Level".
*
* @param name A qualified class name
* @return Whether the name begins with a strip name
*/
boolean qualifiedNameBeginsWithStripType(String name) {
if (name != null) {
for (String type : stripTypes) {
if (name.equals(type)) {
return true;
}
}
for (String type : stripTypePrefixes) {
if (name.startsWith(type)) {
return true;
}
}
}
return false;
}
/**
* Determines whether a NAME node represents a reference to a variable that
* has been removed.
*
* @param t The traversal
* @param n A NAME node
* @return Whether the variable was removed
*/
boolean isReferenceToRemovedVar(NodeTraversal t, Node n) {
String name = n.getString();
Scope scope = t.getScope();
Var var = scope.getVar(name);
return varsToRemove.contains(var);
}
/**
* Gets whether a CALL node triggers statement removal, based on the name
* of the object whose method is being called, or the name of the method.
* Checks whether the name begins with a strip type, includes a field name
* that's a strip name, or belongs to the set of global class-defining
* functions (e.g. goog.inherits).
*
* @param t The traversal
* @param n A CALL node
* @return Whether the node triggers statement removal
*/
boolean isMethodOrCtorCallThatTriggersRemoval(
NodeTraversal t, Node n, Node parent) {
// CALL/NEW
// GETPROP (function) <-- we're interested in this, the function
// GETPROP (callee object) <-- or the object on which it is called
// ...
// STRING (field name)
// STRING (method name)
// ... (arguments)
Node function = n.getFirstChild();
if (function == null || !function.isGetProp()) {
// We are only interested in calls on object references that are
// properties. We don't need to eliminate method calls on variables
// that are getting removed, since that's already done by the code
// that removes all references to those variables.
return false;
}
if (parent != null && parent.isName()) {
Node grandparent = parent.getParent();
if (grandparent != null && NodeUtil.isNameDeclaration(grandparent)) {
// The call's return value is being used to initialize a newly
// declared variable. We should leave the call intact for now.
// That way, when the traversal reaches the variable declaration,
// we'll recognize that the variable and all references to it need
// to be eliminated.
return false;
}
}
Node callee = function.getFirstChild();
return nameIncludesFieldNameToStrip(callee) ||
nameIncludesFieldNameToStrip(function) ||
qualifiedNameBeginsWithStripType(function) ||
actsOnStripType(t, n);
}
/**
* @return Whether a name includes a field name that should be stripped.
* E.g., "foo.stripMe.bar", "(foo.bar).stripMe", etc.
*/
boolean nameIncludesFieldNameToStrip(@Nullable Node n) {
if (n != null && n.isGetProp()) {
Node propNode = n.getLastChild();
return isStripName(propNode.getString())
|| nameIncludesFieldNameToStrip(n.getFirstChild());
}
return false;
}
/**
* Determines whether the given node helps to define a
* strip type. For example, goog.inherits(stripType, Object)
* would be such a call.
*
* Also reports an error if a non-strip type inherits from a strip type.
*
* @param t The current traversal
* @param callNode The CALL node
*/
private boolean actsOnStripType(NodeTraversal t, Node callNode) {
SubclassRelationship classes =
compiler.getCodingConvention().getClassesDefinedByCall(callNode);
if (classes != null) {
// It's okay to strip a type that inherits from a non-stripped type
// e.g. goog.inherits(goog.debug.Logger, Object)
if (qualifiedNameBeginsWithStripType(classes.subclassName)) {
return true;
}
// report an error if a non-strip type inherits from a
// strip type.
if (qualifiedNameBeginsWithStripType(classes.superclassName)) {
t.report(callNode, STRIP_TYPE_INHERIT_ERROR,
classes.subclassName, classes.superclassName);
}
}
return false;
}
/**
* Gets whether a JavaScript identifier is the name of a variable or
* property that should be stripped.
*
* @param name A JavaScript identifier
* @return Whether {@code name} is a name that triggers removal
*/
boolean isStripName(String name) {
if (stripNameSuffixes.contains(name) ||
stripNamePrefixes.contains(name)) {
return true;
}
if (name.isEmpty() || Character.isUpperCase(name.charAt(0))) {
return false;
}
String lcName = name.toLowerCase();
for (String stripName : stripNamePrefixes) {
if (lcName.startsWith(stripName.toLowerCase())) {
return true;
}
}
for (String stripName : stripNameSuffixes) {
if (lcName.endsWith(stripName.toLowerCase())) {
return true;
}
}
return false;
}
/**
* Replaces a node with a NULL node. This is useful where a value is
* expected.
*
* @param n A node
* @param parent {@code n}'s parent
*/
void replaceWithNull(Node n, Node parent) {
parent.replaceChild(n, IR.nullNode());
NodeUtil.markFunctionsDeleted(n, compiler);
}
/**
* Replaces a node with an EMPTY node. This is useful where a statement is
* expected.
*
* @param n A node
* @param parent {@code n}'s parent
*/
void replaceWithEmpty(Node n, Node parent) {
NodeUtil.removeChild(parent, n);
NodeUtil.markFunctionsDeleted(n, compiler);
}
}
}