com.google.errorprone.bugpatterns.nullness.EqualsBrokenForNull 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.nullness;
import static com.google.common.collect.Iterables.getOnlyElement;
import static com.google.errorprone.matchers.Description.NO_MATCH;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import static com.google.errorprone.util.ASTHelpers.isConsideredFinal;
import com.google.errorprone.BugPattern;
import com.google.errorprone.BugPattern.SeverityLevel;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker;
import com.google.errorprone.bugpatterns.BugChecker.MethodTreeMatcher;
import com.google.errorprone.dataflow.nullnesspropagation.Nullness;
import com.google.errorprone.dataflow.nullnesspropagation.NullnessAnalysis;
import com.google.errorprone.fixes.Fix;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matchers;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.IfTree;
import com.sun.source.tree.InstanceOfTree;
import com.sun.source.tree.LambdaExpressionTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.ParenthesizedTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.TypeCastTree;
import com.sun.source.tree.VariableTree;
import com.sun.source.util.TreePath;
import com.sun.source.util.TreePathScanner;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import java.util.HashSet;
import java.util.Set;
import javax.annotation.Nullable;
/**
* {@link BugChecker} adds a null check to {@code equals()} method implementations which don't
* satisfy the null contract of {@link Object#equals} i.e. {@code equals(null)} should return false.
*
* @author [email protected] (Sumit Bhagwani)
*/
@BugPattern(
name = "EqualsBrokenForNull",
summary = "equals() implementation may throw NullPointerException when given null",
severity = SeverityLevel.WARNING)
public class EqualsBrokenForNull extends BugChecker implements MethodTreeMatcher {
@Override
public Description matchMethod(MethodTree tree, VisitorState state) {
if (!Matchers.equalsMethodDeclaration().matches(tree, state)) {
return NO_MATCH;
}
// Keep track of variables which, if true, imply that the incoming variable is non-null.
Set impliesNonNull = new HashSet<>();
Set incomingVariableSymbols = new HashSet<>();
VarSymbol varSymbol = getSymbol(getOnlyElement(tree.getParameters()));
incomingVariableSymbols.add(varSymbol);
NullnessAnalysis analysis = NullnessAnalysis.instance(state.context);
// we run nullness analysis on all the subtrees and match if there is a method invocation on
// the argument to the equals method.
boolean[] crashesWithNull = {false};
new TreePathScanner() {
@Override
public Void visitMemberSelect(MemberSelectTree node, Void unused) {
if (!crashesWithNull[0]) {
Symbol symbol = getSymbol(node.getExpression());
if (symbol instanceof VarSymbol && incomingVariableSymbols.contains(symbol)) {
Nullness nullness =
analysis.getNullness(
new TreePath(getCurrentPath(), node.getExpression()), state.context);
if (nullness == Nullness.NULLABLE) {
crashesWithNull[0] = true;
}
}
}
return super.visitMemberSelect(node, null);
}
@Override
public Void visitVariable(VariableTree variableTree, Void unused) {
// Track variables assigned from our parameter.
Tree initializer = variableTree.getInitializer();
VarSymbol symbol = getSymbol(variableTree);
if (isConsideredFinal(symbol) && initializer instanceof InstanceOfTree) {
InstanceOfTree instanceOf = (InstanceOfTree) initializer;
if (instanceOf.getExpression() instanceof IdentifierTree
&& incomingVariableSymbols.contains(getSymbol(instanceOf.getExpression()))) {
impliesNonNull.add(getSymbol(variableTree));
}
}
if (incomingVariableSymbols.contains(findVariable(variableTree.getInitializer()))) {
incomingVariableSymbols.add(getSymbol(variableTree));
}
return super.visitVariable(variableTree, null);
}
@Override
public Void visitIf(IfTree ifTree, Void unused) {
ExpressionTree condition = ASTHelpers.stripParentheses(ifTree.getCondition());
if (condition instanceof IdentifierTree && impliesNonNull.contains(getSymbol(condition))) {
return scan(ifTree.getElseStatement(), null);
}
return super.visitIf(ifTree, unused);
}
@Override
public Void visitLambdaExpression(LambdaExpressionTree node, Void unused) {
// Our nullness analyzer isn't good at straddling lambda boundaries.
return null;
}
/**
* Unwraps expressions like `(Foo) foo` or `((Foo) foo)` to return the VarSymbol of `foo`, or
* null if the expression wasn't of this form.
*/
@Nullable
private VarSymbol findVariable(Tree tree) {
while (tree != null) {
switch (tree.getKind()) {
case TYPE_CAST:
tree = ((TypeCastTree) tree).getExpression();
break;
case PARENTHESIZED:
tree = ((ParenthesizedTree) tree).getExpression();
break;
case IDENTIFIER:
Symbol symbol = getSymbol(tree);
return symbol instanceof VarSymbol ? (VarSymbol) symbol : null;
default:
return null;
}
}
return null;
}
}.scan(state.getPath(), null);
if (!crashesWithNull[0]) {
return NO_MATCH;
}
String stringAddition = String.format("if (%s == null) { return false; }\n", varSymbol.name);
Fix fix = SuggestedFix.prefixWith(tree.getBody().getStatements().get(0), stringAddition);
return describeMatch(tree, fix);
}
}