/*
* Copyright 2006 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.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.JSDocInfo;
import com.google.javascript.rhino.JSDocInfoBuilder;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.LinkedHashMap;
import java.util.List;
/**
* Checks for non side effecting statements such as
* <pre>
* var s = "this string is "
* "continued on the next line but you forgot the +";
* x == foo(); // should that be '='?
* foo();; // probably just a stray-semicolon. Doesn't hurt to check though
* </pre>
* and generates warnings.
*
*/
final class CheckSideEffects extends AbstractPostOrderCallback
implements HotSwapCompilerPass {
static final DiagnosticType USELESS_CODE_ERROR = DiagnosticType.warning(
"JSC_USELESS_CODE",
"Suspicious code. {0}");
static final String PROTECTOR_FN = "JSCOMPILER_PRESERVE";
private final CheckLevel level;
private final List<Node> problemNodes = Lists.newArrayList();
private final LinkedHashMap<String, String> noSideEffectExterns =
Maps.newLinkedHashMap();
private final AbstractCompiler compiler;
private final boolean protectSideEffectFreeCode;
CheckSideEffects(AbstractCompiler compiler, CheckLevel level,
boolean protectSideEffectFreeCode) {
this.compiler = compiler;
this.level = level;
this.protectSideEffectFreeCode = protectSideEffectFreeCode;
}
@Override
public void process(Node externs, Node root) {
NodeTraversal.traverse(compiler, externs, new GetNoSideEffectExterns());
NodeTraversal.traverse(compiler, root, this);
// Code with hidden side-effect code is common, for example
// accessing "el.offsetWidth" forces a reflow in browsers, to allow this
// will still allowing local dead code removal in general,
// protect the "side-effect free" code in the source.
//
// This also includes function calls such as with document.createElement
if (protectSideEffectFreeCode) {
protectSideEffects();
}
}
@Override
public void hotSwapScript(Node scriptRoot, Node originalRoot) {
NodeTraversal.traverse(compiler, scriptRoot, this);
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
// VOID nodes appear when there are extra semicolons at the BLOCK level.
// I've been unable to think of any cases where this indicates a bug,
// and apparently some people like keeping these semicolons around,
// so we'll allow it.
if (n.isEmpty() ||
n.isComma()) {
return;
}
if (parent == null) {
return;
}
// Do not try to remove a block or an expr result. We already handle
// these cases when we visit the child, and the peephole passes will
// fix up the tree in more clever ways when these are removed.
if (n.isExprResult() || n.isBlock()) {
return;
}
// This no-op statement was there so that JSDoc information could
// be attached to the name. This check should not complain about it.
if (n.isQualifiedName() && n.getJSDocInfo() != null) {
return;
}
boolean isResultUsed = NodeUtil.isExpressionResultUsed(n);
boolean isSimpleOp = NodeUtil.isSimpleOperator(n);
if (!isResultUsed) {
if (isSimpleOp || !NodeUtil.mayHaveSideEffects(n, t.getCompiler())) {
String msg = "This code lacks side-effects. Is there a bug?";
if (n.isString()) {
msg = "Is there a missing '+' on the previous line?";
} else if (isSimpleOp) {
msg = "The result of the '" + Token.name(n.getType()).toLowerCase() +
"' operator is not being used.";
}
t.getCompiler().report(
t.makeError(n, level, USELESS_CODE_ERROR, msg));
// TODO(johnlenz): determine if it is necessary to
// try to protect side-effect free statements as well.
if (!NodeUtil.isStatement(n)) {
problemNodes.add(n);
}
} else if (n.isCall() && (n.getFirstChild().isGetProp() ||
n.getFirstChild().isName() || n.getFirstChild().isString())) {
String qname = n.getFirstChild().getQualifiedName();
// The name should not be defined in src scopes - only externs
boolean isDefinedInSrc = false;
if (qname != null) {
if (n.getFirstChild().isGetProp()) {
Node rootNameNode =
NodeUtil.getRootOfQualifiedName(n.getFirstChild());
isDefinedInSrc = rootNameNode != null && rootNameNode.isName() &&
t.getScope().getVar(rootNameNode.getString()) != null;
} else {
isDefinedInSrc = t.getScope().getVar(qname) != null;
}
}
if (qname != null && noSideEffectExterns.containsKey(qname) &&
!isDefinedInSrc) {
problemNodes.add(n);
String msg = "The result of the extern function call '" + qname +
"' is not being used.";
t.getCompiler().report(
t.makeError(n, level, USELESS_CODE_ERROR, msg));
}
}
}
}
/**
* Protect side-effect free nodes by making them parameters
* to a extern function call. This call will be removed
* after all the optimizations passes have run.
*/
private void protectSideEffects() {
if (!problemNodes.isEmpty()) {
addExtern();
for (Node n : problemNodes) {
Node name = IR.name(PROTECTOR_FN).srcref(n);
name.putBooleanProp(Node.IS_CONSTANT_NAME, true);
Node replacement = IR.call(name).srcref(n);
replacement.putBooleanProp(Node.FREE_CALL, true);
n.getParent().replaceChild(n, replacement);
replacement.addChildToBack(n);
}
compiler.reportCodeChange();
}
}
private void addExtern() {
Node name = IR.name(PROTECTOR_FN);
name.putBooleanProp(Node.IS_CONSTANT_NAME, true);
Node var = IR.var(name);
// Add "@noalias" so we can strip the method when AliasExternals is enabled.
JSDocInfoBuilder builder = new JSDocInfoBuilder(false);
builder.recordNoAlias();
var.setJSDocInfo(builder.build(var));
CompilerInput input = compiler.getSynthesizedExternsInput();
input.getAstRoot(compiler).addChildrenToBack(var);
compiler.reportCodeChange();
}
/**
* Remove side-effect sync functions.
*/
static class StripProtection extends AbstractPostOrderCallback implements CompilerPass {
private final AbstractCompiler compiler;
StripProtection(AbstractCompiler compiler) {
this.compiler = compiler;
}
@Override
public void process(Node externs, Node root) {
NodeTraversal.traverse(compiler, root, this);
}
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isCall()) {
Node target = n.getFirstChild();
// TODO(johnlenz): add this to the coding convention
// so we can remove goog.reflect.sinkValue as well.
if (target.isName() && target.getString().equals(PROTECTOR_FN)) {
Node expr = n.getLastChild();
n.detachChildren();
parent.replaceChild(n, expr);
}
}
}
}
/**
* Get fully qualified function names which are marked
* with @nosideeffects
*
* TODO(ChadKillingsworth) Add support for object literals
*/
private class GetNoSideEffectExterns extends AbstractPostOrderCallback {
@Override
public void visit(NodeTraversal t, Node n, Node parent) {
if (n.isFunction()) {
String name = NodeUtil.getFunctionName(n);
JSDocInfo jsDoc = NodeUtil.getBestJSDocInfo(n);
if (jsDoc != null && jsDoc.isNoSideEffects()) {
noSideEffectExterns.put(name, null);
}
}
}
}
}