com.google.errorprone.bugpatterns.ToStringReturnsNull Maven / Gradle / Ivy
/*
* Copyright 2016 The Error Prone 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.errorprone.bugpatterns;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matchers;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.LambdaExpressionTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.ReturnTree;
import com.sun.source.tree.Tree;
import com.sun.source.util.TreeScanner;
/**
* ToString should not return null.
*
* @author [email protected] (Eleanor Harris)
* @author [email protected] (Siyuan Liu)
*/
@BugPattern(
summary = "An implementation of Object.toString() should never return null.",
severity = WARNING)
public class ToStringReturnsNull extends BugChecker implements MethodTreeMatcher {
@Override
public Description matchMethod(MethodTree tree, VisitorState state) {
if (!Matchers.toStringMethodDeclaration().matches(tree, state)) {
return Description.NO_MATCH;
}
return tree.accept(new FindReturnNullLiteralScanner(), null)
? describeMatch(tree)
: Description.NO_MATCH;
}
private static class FindReturnNullLiteralScanner extends BooleanScanner {
@Override
public Boolean visitLambdaExpression(LambdaExpressionTree node, Void unused) {
return false;
}
@Override
public Boolean visitClass(ClassTree node, Void unused) {
return false;
}
@Override
public Boolean visitReturn(ReturnTree node, Void unused) {
ExpressionTree expression = node.getExpression();
return expression != null && new ReturnExpressionScanner().scan(expression, null);
}
private static class ReturnExpressionScanner extends BooleanScanner {
@Override
public Boolean scan(Tree tree, Void unused) {
switch (tree.getKind()) {
case NULL_LITERAL:
return true;
case PARENTHESIZED:
case CONDITIONAL_EXPRESSION:
return super.scan(tree, unused);
default:
return false;
}
}
}
}
private abstract static class BooleanScanner extends TreeScanner {
@Override
public Boolean scan(Tree tree, Void unused) {
return Boolean.TRUE.equals(super.scan(tree, unused));
}
@Override
public final Boolean reduce(Boolean a, Boolean b) {
return Boolean.TRUE.equals(a) || Boolean.TRUE.equals(b);
}
}
}