com.google.errorprone.bugpatterns.CheckNotNullMultipleTimes Maven / Gradle / Ivy
/*
* Copyright 2019 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 static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.matchers.Matchers.staticMethod;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import static com.google.errorprone.util.ASTHelpers.isConsideredFinal;
import com.google.common.collect.HashMultiset;
import com.google.common.collect.Multiset;
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.Matcher;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.IfTree;
import com.sun.source.tree.LambdaExpressionTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.StatementTree;
import com.sun.source.tree.SwitchTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.TryTree;
import com.sun.source.util.TreePathScanner;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/** Checks for the same variable being checked against null twice in a method. */
@BugPattern(
name = "CheckNotNullMultipleTimes",
severity = ERROR,
summary = "A variable was checkNotNulled multiple times. Did you mean to check something else?")
public final class CheckNotNullMultipleTimes extends BugChecker implements MethodTreeMatcher {
private static final Matcher CHECK_NOT_NULL =
staticMethod().onClass("com.google.common.base.Preconditions").named("checkNotNull");
@Override
public Description matchMethod(MethodTree tree, VisitorState state) {
Multiset variables = HashMultiset.create();
Map lastCheck = new HashMap<>();
new TreePathScanner() {
@Override
public Void visitMethodInvocation(MethodInvocationTree tree, Void unused) {
List arguments = tree.getArguments();
if (!arguments.isEmpty()
&& arguments.get(0) instanceof IdentifierTree
// Only consider side-effects-only calls to checkNotNull: it turns out people often
// intentionally write repeated null-checks for the same variable when using the result
// as a value, and we would have many false positives if we counted those.
&& getCurrentPath().getParentPath().getLeaf() instanceof StatementTree
&& CHECK_NOT_NULL.matches(tree, state)) {
Symbol symbol = getSymbol(arguments.get(0));
if (symbol instanceof VarSymbol && isConsideredFinal(symbol)) {
variables.add((VarSymbol) symbol);
lastCheck.put((VarSymbol) symbol, tree);
}
}
return super.visitMethodInvocation(tree, null);
}
// Don't descend into ifs and switches, given people often repeat the same checks within
// top-level conditional branches.
@Override
public Void visitSwitch(SwitchTree tree, Void unused) {
return null;
}
@Override
public Void visitIf(IfTree tree, Void unused) {
return null;
}
@Override
public Void visitLambdaExpression(LambdaExpressionTree tree, Void unused) {
return null;
}
@Override
public Void visitClass(ClassTree tree, Void unused) {
return null;
}
// Sometimes a variable is checked in the try and the catch blocks of a try statement; don't
// descend into the catch.
// try {
//
// checkNotNull(frobnicator);
//
// } catch (Exception e) {
// checkNotNull(frobnicator);
// }
@Override
public Void visitTry(TryTree tree, Void unused) {
return scan(tree.getBlock(), null);
}
}.scan(state.getPath(), null);
for (Multiset.Entry entry : variables.entrySet()) {
if (entry.getCount() > 1) {
state.reportMatch(
buildDescription(lastCheck.get(entry.getElement()))
.setMessage(
String.format(
"checkNotNull(%s) was called more than once. Did you mean to check"
+ " something else?",
entry.getElement()))
.build());
}
}
return NO_MATCH;
}
}