// Copyright (C) 2009 Google Inc.
//
// 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.caja.parser.js.scope;
import com.google.caja.parser.AncestorChain;
import com.google.caja.parser.ParseTreeNode;
import com.google.caja.parser.js.CatchStmt;
import com.google.caja.parser.js.Declaration;
import com.google.caja.parser.js.ExpressionStmt;
import com.google.caja.parser.js.ForEachLoop;
import com.google.caja.parser.js.FunctionConstructor;
import com.google.caja.parser.js.FunctionDeclaration;
import com.google.caja.parser.js.Identifier;
import com.google.caja.parser.js.Operation;
import com.google.caja.parser.js.Operator;
import com.google.caja.parser.js.OperatorCategory;
import com.google.caja.parser.js.Reference;
import com.google.caja.parser.js.WithStmt;
import com.google.caja.util.Lists;
import com.google.caja.util.Sets;
import java.util.List;
import java.util.Set;
/**
* Examines a snippet of JavaScript code, and publishes events to a
* {@link ScopeListener listener} about declarations in the code, their uses,
* and possibly noteworthy conditions such as masking relationships, duplicate
* declarations, etc.
*
* <h2>Glossary</h2>
* <dl>
* <dt>Name</dt>
* <dd>A JavaScript identifier or special keyword like {@code this}.
* <dt>Scope</dt>
* <dd>A set of names defined in a program AST and any meta-data about those
* definitions or uses of those definitions. When a name is defined in
* a scope, then uses will not fall-through to a parent scope.
* <dt>Containing Scope</dt>
* <dd>A scope "outer" contains "inner" if "outer" corresponds to an AST
* that entirely contains the subtree to which "inner" corresponds.
* <dt>Symbol</dt>
* <dd>A name in a scope.</dd>
* <dt>Declaration</dt>
* <dd>A program construct whose purpose is to add a name to the set of
* names defined in a scope. The set of declarations for a scope is
* statically determinable.</dd>
* <dt>Defined</dt>
* <dd>The state a name is in when a particular scope includes a declaration
* for it ({@code var x}), or when that name has a special meaning in that
* scope ({@code this}). The set of names defined in a scope is not
* statically determinable, e.g. in the case of object properties
* aliased by {@code with} blocks, or in the case of global variables
* introduced by {@code eval}ed code. The set of names defined in a scope
* is a superset of those declared.
* <dt>Masking</dt>
* <dd>A symbol masks another symbol when they have the same name and the
* first appears in a scope that is wholly contained in the other's scope
* so that any uses of the name will not resolve to the symbol in the
* containing scope. A symbol does not mask itself.
* E.g. in <code>var x; function (x) { ... x ... }}</code> the formal
* parameter {@code x} masks the variable {@code x} since uses of
* {@code x} in the function no longer resolve to the variable.
* </dl>
*
* @param <S> the type of scope used by this analyzer to match references to
* a symbol to the scope in which that symbol is defined.
* @author mikesamuel@gmail.com
*/
public abstract class ScopeAnalyzer<S extends AbstractScope> {
private final ScopeListener<S> listener;
protected ScopeAnalyzer(ScopeListener<S> listener) {
if (listener == null) { throw new NullPointerException(); }
this.listener = listener;
}
/**
* @return true if, as in standard EcmaScript, a named function literal
* introduces a name into its body.
*/
protected abstract boolean fnCtorsDeclareInBody();
/**
* @return true if, as in JScript's nonstandard scoping, a named function
* literal introduces a declaration in the containing scope.
*/
protected abstract boolean fnCtorsDeclareInContaining();
/**
* Publishes events about the given JS parse tree to the listener passed to
* the constructor.
*/
public S apply(AncestorChain<? extends ParseTreeNode> ac) {
ScopeTree<S> root = buildScopeTree(ac, null);
publishEvents(root);
return root.scopeImpl;
}
/** Build scope tree and collect declarations and uses. */
private ScopeTree<S> buildScopeTree(AncestorChain<?> ac, ScopeTree<S> outer) {
ScopeTree<S> scope = outer;
ScopeType t = ScopeType.forNode(ac.node);
if (outer == null && (t == null || !t.isDeclarationContainer)) {
t = ScopeType.PROGRAM;
}
if (t != null) { // Start a new scope
scope = new ScopeTree<S>(
outer, t, listener.createScope(t, ac, scopeImpl(outer)));
if (t == ScopeType.WITH) {
// With blocks are odd. A scope corresponds to a tree, but in
// with (obj) body
// obj is resolved in a different LexicalEnvironment than body, so
// cannot be said to be a scope.
// But we can't say that the scope corresponds just to body, since in
// with (obj) (function () { ... })
// the body introduces a scope. This will become more problematic when
// we deal with let-scoped declarations.
AncestorChain<WithStmt> with = ac.cast(WithStmt.class);
buildScopeTree(with.child(with.node.getScopeObject()), outer);
buildScopeTree(with.child(with.node.getBody()), scope);
return scope;
}
}
scope.inScope.add(ac);
if (ac.node instanceof Declaration) {
AncestorChain<Declaration> d = ac.cast(Declaration.class);
AncestorChain<Identifier> id = d.child(d.node.getIdentifier());
Symbol<S> symbol = new Symbol<S>(id, scope);
hoist(id, scope).declarations.add(symbol);
if (d.node.getInitializer() != null || isKeyReceiver(d)) {
scope.uses.add(symbol);
}
} else if (ac.node instanceof Reference) {
AncestorChain<Reference> r = ac.cast(Reference.class);
if (!isPropertyName(r)) {
scope.uses.add(new Symbol<S>(r.child(r.node.getIdentifier()), scope));
}
} else if (ac.node instanceof FunctionConstructor) {
AncestorChain<FunctionConstructor> f = ac.cast(FunctionConstructor.class);
AncestorChain<Identifier> id = f.child(f.node.getIdentifier());
if (id.node.getName() != null) {
if (fnCtorsDeclareInBody()) { // Standard function scoping
scope.declarations.add(new Symbol<S>(id, scope));
}
if (fnCtorsDeclareInContaining() // IE style function scoping
&& ac.parent != null
&& !(ac.parent.node instanceof FunctionDeclaration)) {
scope.outer.declarations.add(new Symbol<S>(id, scope.outer));
}
}
}
for (ParseTreeNode child : ac.node.children()) {
buildScopeTree(ac.child(child), scope);
}
return scope;
}
private void publishEvents(ScopeTree<S> s) {
S scopeImpl = s.scopeImpl;
listener.enterScope(scopeImpl);
for (AncestorChain<?> ac : s.inScope) { listener.inScope(ac, s.scopeImpl); }
for (Symbol<S> decl : s.declarations) { declare(decl.id, decl.useScope); }
// Recurse to inner scopes before handling uses so that all hoisted
// declarations are taken into account before uses are resolved.
for (ScopeTree<S> inner : s.innerScopes) { publishEvents(inner); }
for (Symbol<S> use : s.uses) { handleUse(use.id, use.useScope); }
listener.exitScope(scopeImpl);
}
private void handleUse(AncestorChain<Identifier> id, ScopeTree<S> s) {
ParseTreeNode n = id.parent.node;
if (n instanceof Reference) {
// Now that we're done with all the declaration in the scope, we can
// tell whether a use corresponds to a declaration in the scope.
String symbolName = id.node.getName();
ScopeTree<S> defSite = definingSite(symbolName, s);
Operator assignOperator = assignOperator(id);
if (assignOperator == null) {
listener.read(id, s.scopeImpl, scopeImpl(defSite));
} else if (assignOperator == Operator.ASSIGN) {
listener.assigned(id, s.scopeImpl, scopeImpl(defSite));
} else { // ++foo, foo++, foo += 1 all read before assignment
listener.read(id, s.scopeImpl, scopeImpl(defSite));
listener.assigned(id, s.scopeImpl, scopeImpl(defSite));
}
} else if (n instanceof Declaration) {
ScopeTree<S> defSite = definingSite(id.node.getName(), s);
listener.assigned(id, s.scopeImpl, scopeImpl(defSite));
} else {
throw new ClassCastException("Unexpected use " + n);
}
}
/**
* If the given identifier is the target of an assignment, then returns the
* operator that is assigning it. Otherwise returns null.
*/
private static Operator assignOperator(AncestorChain<Identifier> ac) {
if (ac.parent == null) { return null; }
if (!(ac.parent.node instanceof Reference)) { return null; }
AncestorChain<?> grandparent = ac.parent.parent;
if (grandparent == null) { return null; }
if (grandparent.node instanceof Operation) {
// Handles ++ac, ac += ..., ac = ...
Operation op = grandparent.cast(Operation.class).node;
Operator operator = op.getOperator();
return (operator.getCategory() == OperatorCategory.ASSIGNMENT
&& ac.parent.node == op.children().get(0)) ? operator : null;
} else if (grandparent.node instanceof ExpressionStmt
&& grandparent.parent != null
&& grandparent.parent.node instanceof ForEachLoop) {
// Handle
// for (k in obj) { ... }
ForEachLoop loop = grandparent.parent.cast(ForEachLoop.class).node;
if (grandparent.node == loop.getKeyReceiver()) { return Operator.ASSIGN; }
}
return null;
}
/**
* The scope in which the named symbol is defined or null if it is a free
* variable.
* @param useSite the scope in which symbol is referenced.
*/
private ScopeTree<S> definingSite(String symbolName, ScopeTree<S> useSite) {
if ("this".equals(symbolName)) {
// "this" is defined in function & program scopes, and cannot be declared.
for (ScopeTree<S> s = useSite; s != null; s = s.outer) {
if (s.type == ScopeType.FUNCTION || s.type == ScopeType.PROGRAM) {
return s;
}
}
} else if ("arguments".equals(symbolName)) {
// "arguments" is defined in all functions, but can be declared as well.
for (ScopeTree<S> s = useSite; s != null; s = s.outer) {
if (s.type == ScopeType.FUNCTION || s.declared.contains(symbolName)) {
return s;
}
}
} else {
for (ScopeTree<S> s = useSite; s != null; s = s.outer) {
if (s.declared.contains(symbolName)) { return s; }
}
}
return null;
}
/**
* True if the given reference refers to a property name.
* E.g. {@code bar} in {@code foo.bar}.
* Any reference in a {@code with} statement could refer to a property name
* at some times in a program, and not in others.
* This does not handle that distinction.
*/
private static boolean isPropertyName(AncestorChain<Reference> ac) {
return (ac.parent != null
&& Operation.is(ac.parent.node, Operator.MEMBER_ACCESS)
&& ac.node == ac.parent.node.children().get(1));
}
/**
* True iff ac receives the object key value as does {@code k} in
* {@code for(var k in obj)}.
*/
private static boolean isKeyReceiver(AncestorChain<Declaration> ac) {
return (ac.parent != null
&& ac.parent.node instanceof ForEachLoop
&& ac.node == ac.parent.node.children().get(0));
}
/**
* The name that a right hand side expression is assigned to.
* @param ac a right hand side expression.
* @return null if no such name.
*/
private static String nameAssignedTo(AncestorChain<?> ac) {
if (ac.parent == null) { return null; }
if (ac.parent.node instanceof Declaration) {
return ac.parent.cast(Declaration.class).node.getIdentifierName();
} else if (Operation.is(ac.parent.node, Operator.ASSIGN)) {
ParseTreeNode lhs = ac.parent.node.children().get(0);
return lhs instanceof Reference ?
((Reference) lhs).getIdentifierName() : null;
}
return null;
}
/**
* Returns the scope into which the given declaration should be hoisted.
* @param id an identifier being declared.
* @param scope the scope in which the identifier appears.
*/
private ScopeTree<S> hoist(AncestorChain<Identifier> id, ScopeTree<S> scope) {
ScopeTree<S> declScope = scope;
if (id.parent.parent == null
|| !(id.parent.parent.node instanceof CatchStmt)) {
// If it's not an exception declaration,
// we have to hoist the declaration out of any non-declaration scopes.
while (!declScope.type.isDeclarationContainer) {
declScope = declScope.outer;
}
}
return declScope;
}
/** Fire declaration, masking, and overriding events, and update scope */
private void declare(AncestorChain<Identifier> id, ScopeTree<S> scope) {
String symbolName = id.node.getName();
ScopeTree<S> declScope = hoist(id, scope);
for (ScopeTree<S> s = scope; s != declScope; s = s.outer) {
if (s.type != ScopeType.CATCH) { continue; }
AncestorChain<CatchStmt> cs = s.inScope.get(0).cast(CatchStmt.class);
AncestorChain<Declaration> ex = cs.child(cs.node.getException());
Identifier exId = ex.node.getIdentifier();
if (symbolName.equals(exId.getName())) {
listener.splitInitialization(
id, declScope.scopeImpl, ex.child(exId), s.scopeImpl);
}
}
ScopeTree<S> maskedScope = definingSite(symbolName, declScope);
declScope.declared.add(symbolName);
listener.declaration(id, declScope.scopeImpl);
if (maskedScope != null
// Not a function declaration or a var declaration like
// var x = function x() { ... };
&& !(id.parent.node instanceof FunctionConstructor
&& symbolName.equals(nameAssignedTo(id.parent)))) {
if (maskedScope == scope) {
listener.duplicate(id, declScope.scopeImpl);
} else {
listener.masked(id, declScope.scopeImpl, scopeImpl(maskedScope));
}
}
}
/**
* @return null if the input is null which is the case for the declaration
* scopes of free variables.
*/
private static <S extends AbstractScope> S scopeImpl(ScopeTree<S> s) {
return s != null ? s.scopeImpl : null;
}
/** Encapsulates a scope and its uses and declarations. */
private static final class ScopeTree<S> {
/** The scope that contains this scope tree or null if this is the root. */
final ScopeTree<S> outer;
final ScopeType type;
/** The listener defined scope corresponding to this scope tree. */
final S scopeImpl;
/** The inner scopes contained by this scope, non-transitively. */
final List<ScopeTree<S>> innerScopes = Lists.newArrayList();
/** The set of AST nodes in this scope that are not in an inner scope. */
final List<AncestorChain<?>> inScope = Lists.newArrayList();
/**
* The symbols corresponding to declarations in this scope,
* non-transitively.
* These may not be declared in this scope because of hoisting.
*/
final List<Symbol<S>> declarations = Lists.newArrayList();
/** The symbols corresponding to uses in this scope. */
final List<Symbol<S>> uses = Lists.newArrayList();
/** The set of names declared in this scope. */
final Set<String> declared = Sets.newHashSet();
ScopeTree(ScopeTree<S> outer, ScopeType t, S scopeImpl) {
this.outer = outer;
this.type = t;
this.scopeImpl = scopeImpl;
if (outer != null) { outer.innerScopes.add(this); }
}
}
/** An identifier in a specific scope. */
private static final class Symbol<S> {
final AncestorChain<Identifier> id;
final ScopeTree<S> useScope;
Symbol(AncestorChain<Identifier> id, ScopeTree<S> useScope) {
this.id = id;
this.useScope = useScope;
}
}
}