com.google.errorprone.bugpatterns.ComparingThisWithNull Maven / Gradle / Ivy
/*
* Copyright 2018 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.ERROR;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.BinaryTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.google.errorprone.matchers.Matchers;
import com.sun.source.tree.BinaryTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.Tree.Kind;
/** Check for expressions containing {@code this != null} or {@code this == null} */
@BugPattern(
name = "ComparingThisWithNull",
summary = "this == null is always false, this != null is always true",
explanation =
"The boolean expression this != null always returns true"
+ " and similarly this == null always returns false.",
severity = ERROR)
public class ComparingThisWithNull extends BugChecker implements BinaryTreeMatcher {
private static final Matcher EQUAL_OR_NOT_EQUAL =
Matchers.allOf(
Matchers.anyOf(Matchers.kindIs(Kind.EQUAL_TO), Matchers.kindIs(Kind.NOT_EQUAL_TO)),
Matchers.binaryTree(Matchers.kindIs(Kind.NULL_LITERAL), new ThisMatcher()));
@Override
public Description matchBinary(BinaryTree tree, VisitorState state) {
if (EQUAL_OR_NOT_EQUAL.matches(tree, state)) {
return describeMatch(tree);
}
return Description.NO_MATCH;
}
private static class ThisMatcher implements Matcher {
@Override
public boolean matches(ExpressionTree thisExpression, VisitorState state) {
if (thisExpression.getKind().equals(Kind.IDENTIFIER)) {
IdentifierTree identifier = (IdentifierTree) thisExpression;
if (identifier.getName().contentEquals("this")) {
return true;
}
}
return false;
}
}
}