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/*
* Copyright 2004 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.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Strings.nullToEmpty;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ListMultimap;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.jscomp.NodeTraversal.ScopedCallback;
import com.google.javascript.rhino.Node;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import javax.annotation.Nullable;
/**
* RenameVars renames all the variables names into short names, to reduce code
* size and also to obfuscate the code.
*/
final class RenameVars implements CompilerPass {
/**
* Limit on number of locals in a scope for temporary local renaming
* when {@code preferStableNames} is true.
*/
private static final int MAX_LOCALS_IN_SCOPE_TO_TEMP_RENAME = 1000;
private final AbstractCompiler compiler;
/** List of global NAME nodes */
private final ArrayList globalNameNodes = new ArrayList<>();
/** List of local NAME nodes */
private final ArrayList localNameNodes = new ArrayList<>();
/** Mapping of original names for change detection */
private final Map originalNameByNode = new HashMap<>();
/**
* Maps a name node to its pseudo name, null if we are not generating so
* there will be no overhead unless we are debugging.
*/
private final Map pseudoNameMap;
/** Set of extern variable names */
private Set externNames;
/** Set of reserved variable names */
private final Set reservedNames;
/** The renaming map */
private final Map renameMap = new HashMap<>();
/** The previously used rename map. */
private final VariableMap prevUsedRenameMap;
/** The global name prefix */
private final String prefix;
/** Counter for each assignment */
private int assignmentCount = 0;
// Logic for bleeding functions, where the name leaks into the outer
// scope on IE but not on other browsers.
private final Set localBleedingFunctions = new HashSet<>();
private final ListMultimap localBleedingFunctionsPerScope =
ArrayListMultimap.create();
class Assignment {
final boolean isLocal;
final String oldName;
final int orderOfOccurrence;
String newName;
int count; // Number of times this is referenced
Assignment(String name) {
this.isLocal = name.startsWith(LOCAL_VAR_PREFIX);
this.oldName = name;
this.newName = null;
this.count = 0;
// Represents the order at which a symbol appears in the source.
this.orderOfOccurrence = assignmentCount++;
}
/**
* Assigns the new name.
*/
void setNewName(String newName) {
checkState(this.newName == null);
this.newName = newName;
}
}
/** Maps an old name to a new name assignment */
private final Map assignments =
new HashMap<>();
/** Whether renaming should apply to local variables only. */
private final boolean localRenamingOnly;
/**
* Whether function expression names should be preserved. Typically, for
* debugging purposes.
*
* @see NameAnonymousFunctions
*/
private final boolean preserveFunctionExpressionNames;
private final boolean preferStableNames;
/** Characters that shouldn't be used in variable names. */
private final char[] reservedCharacters;
/** A prefix to distinguish temporary local names from global names */
private static final String LOCAL_VAR_PREFIX = "L ";
// Shared name generator
private final NameGenerator nameGenerator;
/*
* nameGenerator is a shared NameGenerator that this instance can use;
* the instance may reset or reconfigure it, so the caller should
* not expect any state to be preserved.
*/
RenameVars(
AbstractCompiler compiler,
String prefix,
boolean localRenamingOnly,
boolean preserveFunctionExpressionNames,
boolean generatePseudoNames,
boolean preferStableNames,
VariableMap prevUsedRenameMap,
@Nullable char[] reservedCharacters,
@Nullable Set reservedNames,
NameGenerator nameGenerator) {
this.compiler = compiler;
this.prefix = nullToEmpty(prefix);
this.localRenamingOnly = localRenamingOnly;
this.preserveFunctionExpressionNames = preserveFunctionExpressionNames;
if (generatePseudoNames) {
this.pseudoNameMap = new HashMap<>();
} else {
this.pseudoNameMap = null;
}
this.prevUsedRenameMap = prevUsedRenameMap;
this.reservedCharacters = reservedCharacters;
this.preferStableNames = preferStableNames;
if (reservedNames == null) {
this.reservedNames = new HashSet<>();
} else {
this.reservedNames = new HashSet<>(reservedNames);
}
this.nameGenerator = nameGenerator;
}
/**
* Iterate through the nodes, collect all the NAME nodes that need to be
* renamed, and count how many times each variable name is referenced.
*
* Keep track of all name references in globalNameNodes, and localNameNodes.
*
* To get shorter local variable renaming, we rename local variables to a
* temporary name "LOCAL_VAR_PREFIX + index" where index is the index of the
* variable declared in the local scope stack.
* e.g.
* Foo(fa, fb) {
* var c = function(d, e) { return fa; }
* }
* The indexes are: fa:0, fb:1, c:2, d:3, e:4
*
* In that way, local variable names are reused in each global function.
* e.g. the final code might look like
* function x(a,b) { ... }
* function y(a,b,c) { ... }
*/
class ProcessVars extends AbstractPostOrderCallback implements ScopedCallback {
@Override
public void enterScope(NodeTraversal t) {
if (t.inGlobalHoistScope() || !shouldTemporarilyRenameLocalsInScope(t.getScope())) {
return;
}
Scope scope = t.getScope();
for (Var current : scope.getVarIterable()) {
if (current.isBleedingFunction()) {
localBleedingFunctions.add(current);
localBleedingFunctionsPerScope.put(
scope.getParent(), current);
}
}
}
@Override
public void exitScope(NodeTraversal t) {}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (!(n.isName() || n.isImportStar())) {
return;
}
String name = n.getString();
// Ignore anonymous functions and classes.
if (name.isEmpty()) {
return;
}
// "import {x as y} from 'm';"
// Skip x because it's not a variable in this scope.
if (parent.isImportSpec() && parent.hasTwoChildren() && parent.getFirstChild() == n) {
return;
}
// Is this local or Global?
// Bleeding functions should be treated as part of their outer
// scope, because IE has bugs in how it handles bleeding
// functions.
Var var = t.getScope().getVar(name);
boolean local =
var != null
&& var.isLocal()
&& (var.getScope().getParent().isLocal() || !var.isBleedingFunction());
// Never rename references to the arguments array
if (var != null && var.isArguments()) {
reservedNames.add(name);
return;
}
// Are we renaming global variables?
if (!local && localRenamingOnly) {
reservedNames.add(name);
return;
}
// Are we renaming function expression names?
if (preserveFunctionExpressionNames && var != null
&& NodeUtil.isFunctionExpression(var.getParentNode())) {
reservedNames.add(name);
return;
}
// Check if we can rename this.
if (!okToRenameVar(name, local)) {
if (local) {
// Blindly de-uniquify for the Prototype library for
// http://blickly.github.io/closure-compiler-issues/#103
String newName = MakeDeclaredNamesUnique.ContextualRenameInverter.getOriginalName(name);
if (!newName.equals(name)) {
n.setString(newName);
}
}
return;
}
if (pseudoNameMap != null) {
recordPseudoName(n);
}
if (local && shouldTemporarilyRenameLocalsInScope(var.getScope())) {
// Give local variables a temporary name based on the
// variable's index in the scope to enable name reuse across
// locals in independent scopes.
String tempName = LOCAL_VAR_PREFIX + getLocalVarIndex(var);
incCount(tempName);
localNameNodes.add(n);
// Remember the original string in a name before it's temporarily filled with an "L".
originalNameByNode.put(n, n.getString());
n.setString(tempName);
} else if (var != null) { // Not an extern
// If it's global, increment global count
incCount(name);
globalNameNodes.add(n);
}
}
// Increment count of an assignment
void incCount(String name) {
Assignment s = assignments.get(name);
if (s == null) {
s = new Assignment(name);
assignments.put(name, s);
}
s.count++;
}
}
/**
* Sorts Assignment objects by their count, breaking ties by their order of
* occurrence in the source to ensure a deterministic total ordering.
*/
private static final Comparator FREQUENCY_COMPARATOR =
new Comparator() {
@Override
public int compare(Assignment a1, Assignment a2) {
if (a1.count != a2.count) {
return a2.count - a1.count;
}
// Break a tie using the order in which the variable first appears in
// the source.
return ORDER_OF_OCCURRENCE_COMPARATOR.compare(a1, a2);
}
};
/**
* Sorts Assignment objects by the order the variable name first appears in
* the source.
*/
private static final Comparator ORDER_OF_OCCURRENCE_COMPARATOR =
new Comparator() {
@Override
public int compare(Assignment a1, Assignment a2) {
return a1.orderOfOccurrence - a2.orderOfOccurrence;
}
};
@Override
public void process(Node externs, Node root) {
this.externNames = NodeUtil.collectExternVariableNames(this.compiler, externs);
originalNameByNode.clear();
// Do variable reference counting.
NodeTraversal.traverse(compiler, root, new ProcessVars());
// Make sure that new names don't overlap with extern names.
reservedNames.addAll(externNames);
// Rename vars, sorted by frequency of occurrence to minimize code size.
SortedSet varsByFrequency = new TreeSet<>(FREQUENCY_COMPARATOR);
varsByFrequency.addAll(assignments.values());
// First try to reuse names from an earlier compilation.
if (prevUsedRenameMap != null) {
reusePreviouslyUsedVariableMap(varsByFrequency);
}
// Assign names, sorted by descending frequency to minimize code size.
assignNames(varsByFrequency);
// Rename the globals!
for (Node n : globalNameNodes) {
setNameAndReport(n, getNewGlobalName(n));
}
// Rename the locals!
for (Node n : localNameNodes) {
setNameAndReport(n, getNewLocalName(n));
}
}
private void setNameAndReport(Node n, @Nullable String newName) {
// A null newName, indicates it should not be renamed.
if (newName != null && !newName.equals(n.getString())) {
n.setString(newName);
// Only mark changes if the final name change is different than it was original before being
// filled with the "L" temporary name.
if (!newName.equals(originalNameByNode.get(n))) {
compiler.reportChangeToEnclosingScope(n);
Node parent = n.getParent();
if (parent.isFunction() && NodeUtil.isFunctionDeclaration(parent)) {
// If we are renaming a function declaration, make sure the containing scope
// has the opportunity to act on the change.
compiler.reportChangeToEnclosingScope(parent);
}
}
}
}
@Nullable
private String getNewGlobalName(Node n) {
String oldName = n.getString();
Assignment a = assignments.get(oldName);
if (a.newName != null && !a.newName.equals(oldName)) {
if (pseudoNameMap != null) {
return pseudoNameMap.get(n);
}
return a.newName;
} else {
return null;
}
}
@Nullable
private String getNewLocalName(Node n) {
String oldTempName = n.getString();
Assignment a = assignments.get(oldTempName);
if (!a.newName.equals(oldTempName)) {
if (pseudoNameMap != null) {
return pseudoNameMap.get(n);
}
return a.newName;
}
return null;
}
private void recordPseudoName(Node n) {
// Variable names should be in a different name space than
// property pseudo names.
pseudoNameMap.put(n, '$' + n.getString() + "$$");
}
/**
* Runs through the assignments and reuses as many names as possible from the previously used
* variable map. Updates reservedNames with the set of names that were reused.
*/
private void reusePreviouslyUsedVariableMap(SortedSet varsToRename) {
// If prevUsedRenameMap had duplicate values then this pass would be
// non-deterministic.
// In such a case, the following will throw an IllegalArgumentException.
checkNotNull(prevUsedRenameMap.getNewNameToOriginalNameMap());
for (Assignment a : varsToRename) {
String prevNewName = prevUsedRenameMap.lookupNewName(a.oldName);
if (prevNewName == null || reservedNames.contains(prevNewName)) {
continue;
}
if (a.isLocal
|| (!externNames.contains(a.oldName)
&& prevNewName.startsWith(prefix))) {
reservedNames.add(prevNewName);
finalizeNameAssignment(a, prevNewName);
}
}
}
/**
* Determines which new names to substitute for the original names.
*/
private void assignNames(SortedSet varsToRename) {
nameGenerator.reset(reservedNames, prefix, reservedCharacters);
NameGenerator globalNameGenerator = nameGenerator;
// Local variables never need a prefix.
// Also, we need to avoid conflicts between global and local variable
// names; we do this by having using the same generator (not two
// instances). The case where global variables have a prefix (and
// therefore we use two different generators) but a local variable name
// might nevertheless conflict with a global one is not handled.
NameGenerator localNameGenerator =
prefix.isEmpty()
? globalNameGenerator
: nameGenerator.clone(reservedNames, "", reservedCharacters);
// Generated names and the assignments for non-local vars.
List pendingAssignments = new ArrayList<>();
List generatedNamesForAssignments = new ArrayList<>();
for (Assignment a : varsToRename) {
if (a.newName != null) {
continue;
}
if (externNames.contains(a.oldName)) {
continue;
}
String newName;
if (a.isLocal) {
// For local variable, we make the assignment right away.
newName = localNameGenerator.generateNextName();
finalizeNameAssignment(a, newName);
} else {
// For non-local variable, delay finalizing the name assignment
// until we know how many new names we'll have of length 2, 3, etc.
newName = globalNameGenerator.generateNextName();
pendingAssignments.add(a);
generatedNamesForAssignments.add(newName);
}
reservedNames.add(newName);
}
// Now that we have a list of generated names, and a list of variable
// Assignment objects, we assign the generated names to the vars as
// follows:
// 1) The most frequent vars get the shorter names.
// 2) If N number of vars are going to be assigned names of the same
// length, we assign the N names based on the order at which the vars
// first appear in the source. This makes the output somewhat less
// random, because symbols declared close together are assigned names
// that are quite similar. With this heuristic, the output is more
// compressible.
// For instance, the output may look like:
// var da = "..", ea = "..";
// function fa() { .. } function ga() { .. }
int numPendingAssignments = generatedNamesForAssignments.size();
for (int i = 0; i < numPendingAssignments;) {
SortedSet varsByOrderOfOccurrence =
new TreeSet<>(ORDER_OF_OCCURRENCE_COMPARATOR);
// Add k number of Assignment to the set, where k is the number of
// generated names of the same length.
int len = generatedNamesForAssignments.get(i).length();
for (int j = i; j < numPendingAssignments
&& generatedNamesForAssignments.get(j).length() == len; j++) {
varsByOrderOfOccurrence.add(pendingAssignments.get(j));
}
// Now, make the assignments
for (Assignment a : varsByOrderOfOccurrence) {
finalizeNameAssignment(a, generatedNamesForAssignments.get(i));
++i;
}
}
}
/**
* Makes a final name assignment.
*/
private void finalizeNameAssignment(Assignment a, String newName) {
a.setNewName(newName);
// Keep track of the mapping
renameMap.put(a.oldName, newName);
}
/**
* Gets the variable map.
*/
VariableMap getVariableMap() {
return new VariableMap(ImmutableMap.copyOf(renameMap));
}
/**
* Determines whether a variable name is okay to rename.
*/
private boolean okToRenameVar(String name, boolean isLocal) {
return !compiler.getCodingConvention().isExported(name, isLocal);
}
/**
* Returns the index within the scope stack.
* e.g. function Foo(a) { var b; function c(d) { } }
* a = 0, b = 1, c = 2, d = 3
*/
private int getLocalVarIndex(Var v) {
int num = v.getIndex();
Scope s = v.getScope().getParent();
if (s == null) {
throw new IllegalArgumentException("Var is not local");
}
boolean isBleedingIntoScope = s.getParent() != null && localBleedingFunctions.contains(v);
while (s.getParent() != null) {
if (isBleedingIntoScope) {
num += localBleedingFunctionsPerScope.get(s).indexOf(v) + 1;
isBleedingIntoScope = false;
} else {
num += localBleedingFunctionsPerScope.get(s).size();
}
if (shouldTemporarilyRenameLocalsInScope(s)) {
num += s.getVarCount();
}
s = s.getParent();
}
return num;
}
/**
* Returns true if the local variables in a scope should be given
* temporary names (eg, 'L 123') prior to renaming to allow reuse of
* names across scopes. With {@code preferStableNames}, temporary
* renaming is disabled if the number of locals in the scope is
* above a heuristic threshold to allow effective reuse of rename
* maps (see {@code prevUsedRenameMap}). In scopes with many
* variables the temporary name given to a variable is unlikely to
* be the same temporary name used when the rename map was created.
*/
private boolean shouldTemporarilyRenameLocalsInScope(Scope s) {
return (!preferStableNames || s.getVarCount() <= MAX_LOCALS_IN_SCOPE_TO_TEMP_RENAME);
}
}
