/*
* Copyright 2017 Google Inc. All Rights Reserved.
*
* 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.errorprone.bugpatterns;
import static com.google.common.base.MoreObjects.firstNonNull;
import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.DoWhileLoopTreeMatcher;
import com.google.errorprone.bugpatterns.BugChecker.ForLoopTreeMatcher;
import com.google.errorprone.bugpatterns.BugChecker.WhileLoopTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.AssignmentTree;
import com.sun.source.tree.BinaryTree;
import com.sun.source.tree.CompoundAssignmentTree;
import com.sun.source.tree.DoWhileLoopTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.ForLoopTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.LiteralTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.UnaryTree;
import com.sun.source.tree.WhileLoopTree;
import com.sun.source.util.SimpleTreeVisitor;
import com.sun.source.util.TreeScanner;
import com.sun.tools.javac.code.Symbol;
/** @author cushon@google.com (Liam Miller-Cushon) */
@BugPattern(
name = "LoopConditionChecker",
category = JDK,
summary = "Loop condition is never modified in loop body.",
severity = ERROR
)
public class LoopConditionChecker extends BugChecker
implements ForLoopTreeMatcher, DoWhileLoopTreeMatcher, WhileLoopTreeMatcher {
@Override
public Description matchDoWhileLoop(DoWhileLoopTree tree, VisitorState state) {
return check(tree.getCondition(), ImmutableList.of(tree.getCondition(), tree.getStatement()));
}
@Override
public Description matchForLoop(ForLoopTree tree, VisitorState state) {
if (tree.getCondition() == null) {
return NO_MATCH;
}
return check(
tree.getCondition(),
ImmutableList.<Tree>builder()
.add(tree.getCondition())
.add(tree.getStatement())
.addAll(tree.getUpdate())
.build());
}
@Override
public Description matchWhileLoop(WhileLoopTree tree, VisitorState state) {
return check(tree.getCondition(), ImmutableList.of(tree.getCondition(), tree.getStatement()));
}
private Description check(ExpressionTree condition, ImmutableList<Tree> loopBodyTrees) {
ImmutableSet<Symbol.VarSymbol> conditionVars = LoopConditionVisitor.scan(condition);
if (conditionVars.isEmpty()) {
return NO_MATCH;
}
for (Tree tree : loopBodyTrees) {
if (UpdateScanner.scan(tree, conditionVars)) {
return NO_MATCH;
}
}
return buildDescription(condition)
.setMessage(
String.format(
"condition variable(s) never modified in loop body: %s",
Joiner.on(", ").join(conditionVars)))
.build();
}
/** Scan for loop conditions that are determined entirely by the state of local variables. */
private static class LoopConditionVisitor extends SimpleTreeVisitor<Boolean, Void> {
static ImmutableSet<Symbol.VarSymbol> scan(Tree tree) {
ImmutableSet.Builder<Symbol.VarSymbol> conditionVars = ImmutableSet.builder();
if (!firstNonNull(tree.accept(new LoopConditionVisitor(conditionVars), null), false)) {
return ImmutableSet.of();
}
return conditionVars.build();
}
private final ImmutableSet.Builder<Symbol.VarSymbol> conditionVars;
public LoopConditionVisitor(ImmutableSet.Builder<Symbol.VarSymbol> conditionVars) {
this.conditionVars = conditionVars;
}
@Override
public Boolean visitIdentifier(IdentifierTree tree, Void unused) {
Symbol sym = ASTHelpers.getSymbol(tree);
if (sym instanceof Symbol.VarSymbol) {
switch (sym.getKind()) {
case LOCAL_VARIABLE:
case PARAMETER:
conditionVars.add((Symbol.VarSymbol) sym);
return true;
default: // fall out
}
}
return false;
}
@Override
public Boolean visitLiteral(LiteralTree tree, Void unused) {
return true;
}
@Override
public Boolean visitUnary(UnaryTree node, Void aVoid) {
return node.getExpression().accept(this, null);
}
@Override
public Boolean visitBinary(BinaryTree node, Void aVoid) {
return firstNonNull(node.getLeftOperand().accept(this, null), false)
&& firstNonNull(node.getRightOperand().accept(this, null), false);
}
}
/** Scan for updates to the given variables. */
private static class UpdateScanner extends TreeScanner<Void, Void> {
public static boolean scan(Tree tree, ImmutableSet<Symbol.VarSymbol> variables) {
UpdateScanner scanner = new UpdateScanner(variables);
tree.accept(scanner, null);
return scanner.modified;
}
private boolean modified = false;
private final ImmutableSet<Symbol.VarSymbol> variables;
public UpdateScanner(ImmutableSet<Symbol.VarSymbol> variables) {
this.variables = variables;
}
@Override
public Void visitUnary(UnaryTree tree, Void unused) {
switch (tree.getKind()) {
case POSTFIX_INCREMENT:
case PREFIX_INCREMENT:
case POSTFIX_DECREMENT:
case PREFIX_DECREMENT:
check(tree.getExpression());
break;
default: // fall out
}
return super.visitUnary(tree, unused);
}
@Override
public Void visitMethodInvocation(MethodInvocationTree tree, Void unused) {
check(ASTHelpers.getReceiver(tree));
return super.visitMethodInvocation(tree, unused);
}
@Override
public Void visitAssignment(AssignmentTree tree, Void unused) {
check(tree.getVariable());
return super.visitAssignment(tree, unused);
}
@Override
public Void visitCompoundAssignment(CompoundAssignmentTree tree, Void unused) {
check(tree.getVariable());
return super.visitCompoundAssignment(tree, unused);
}
private void check(ExpressionTree expression) {
Symbol sym = ASTHelpers.getSymbol(expression);
modified |= variables.contains(sym);
}
}
}