/*
* 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.NodeTraversal.Callback;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
/**
* Checks for certain uses of the {@code this} keyword that are considered
* unsafe because they are likely to reference the global {@code this} object
* unintentionally.
*
* <p>A use of {@code this} is considered unsafe if it's on the left side of an
* assignment or a property access, and not inside one of the following:
* <ol>
* <li>a prototype method
* <li>a function annotated with {@code @constructor}
* <li>a function annotated with {@code @this}.
* <li>a function where there's no logical place to put a
* {@code this} annotation.
* </ol>
*
* <p>Note that this check does not track assignments of {@code this} to
* variables or objects. The code
* <pre>
* function evil() {
* var a = this;
* a.useful = undefined;
* }
* </pre>
* will not get flagged, even though it is semantically equivalent to
* <pre>
* function evil() {
* this.useful = undefined;
* }
* </pre>
* which would get flagged.
*
*/
final class CheckGlobalThis implements Callback {
static final DiagnosticType GLOBAL_THIS = DiagnosticType.warning(
"JSC_USED_GLOBAL_THIS",
"dangerous use of the global 'this' object");
private final AbstractCompiler compiler;
/**
* If {@code assignLhsChild != null}, then the node being traversed is
* a descendant of the first child of an ASSIGN node. assignLhsChild's
* parent is this ASSIGN node.
*/
private Node assignLhsChild = null;
CheckGlobalThis(AbstractCompiler compiler) {
this.compiler = compiler;
}
/**
* Since this pass reports errors only when a global {@code this} keyword
* is encountered, there is no reason to traverse non global contexts.
*/
@Override
public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
if (n.isFunction()) {
// Arrow functions automatically get the "this" value from the
// enclosing scope. e.g. the "this" in
// Foo.prototype.getBar = () => this.bar;
// is the global "this", not an instance of Foo.
if (n.isArrowFunction()) {
return true;
}
// Don't traverse functions that are constructors or have the @this
// or @override annotation.
JSDocInfo jsDoc = getFunctionJsDocInfo(n);
if (jsDoc != null &&
(jsDoc.isConstructor() ||
jsDoc.isInterface() ||
jsDoc.hasThisType() ||
jsDoc.isOverride())) {
return false;
}
// Don't traverse functions unless they would normally
// be able to have a @this annotation associated with them. e.g.,
// var a = function() { }; // or
// function a() {} // or
// a.x = function() {}; // or
// var a = {x: function() {}};
int pType = parent.getType();
if (!(pType == Token.BLOCK ||
pType == Token.SCRIPT ||
pType == Token.NAME ||
pType == Token.ASSIGN ||
// object literal keys
pType == Token.STRING_KEY)) {
return false;
}
// Don't traverse functions that are getting lent to a prototype.
Node gramps = parent.getParent();
if (NodeUtil.isObjectLitKey(parent)) {
JSDocInfo maybeLends = gramps.getJSDocInfo();
if (maybeLends != null &&
maybeLends.getLendsName() != null &&
maybeLends.getLendsName().endsWith(".prototype")) {
return false;
}
}
}
if (parent != null && parent.isAssign()) {
Node lhs = parent.getFirstChild();
if (n == lhs) {
// Always traverse the left side of the assignment. To handle
// nested assignments properly (e.g., (a = this).property = c;),
// assignLhsChild should not be overridden.
if (assignLhsChild == null) {
assignLhsChild = lhs;
}
} else {
// Only traverse the right side if it's not an assignment to a prototype
// property or subproperty.
if (NodeUtil.isGet(lhs)) {
if (lhs.isGetProp() &&
lhs.getLastChild().getString().equals("prototype")) {
return false;
}
Node llhs = lhs.getFirstChild();
if (llhs.isGetProp() &&
llhs.getLastChild().getString().equals("prototype")) {
return false;
}
}
}
}
return true;
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isThis() && shouldReportThis(n)) {
compiler.report(t.makeError(n, GLOBAL_THIS));
}
if (n == assignLhsChild) {
assignLhsChild = null;
}
}
private boolean shouldReportThis(Node n) {
Node parent = n.getParent();
if (assignLhsChild != null) {
// Always report a THIS on the left side of an assign.
return true;
}
// Also report a THIS with a property access.
return parent != null && NodeUtil.isGet(parent);
}
/**
* Gets a function's JSDoc information, if it has any. Checks for a few
* patterns (ellipses show where JSDoc would be):
* <pre>
* ... function() {}
* ... x = function() {};
* var ... x = function() {};
* ... var x = function() {};
* </pre>
*/
private static JSDocInfo getFunctionJsDocInfo(Node n) {
JSDocInfo jsDoc = n.getJSDocInfo();
Node parent = n.getParent();
if (jsDoc == null) {
int parentType = parent.getType();
if (parentType == Token.NAME || parentType == Token.ASSIGN) {
jsDoc = parent.getJSDocInfo();
if (jsDoc == null && parentType == Token.NAME) {
Node gramps = parent.getParent();
if (gramps.isVar()) {
jsDoc = gramps.getJSDocInfo();
}
}
}
}
return jsDoc;
}
}