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/*
* 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.WARNING;
import static com.google.errorprone.matchers.Matchers.anyOf;
import static com.google.errorprone.matchers.Matchers.equalsMethodDeclaration;
import static com.google.errorprone.matchers.Matchers.hashCodeMethodDeclaration;
import static com.google.errorprone.matchers.Matchers.instanceEqualsInvocation;
import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
import static com.google.errorprone.util.ASTHelpers.getReceiver;
import static com.google.errorprone.util.ASTHelpers.getSymbol;
import com.google.common.base.Ascii;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.errorprone.BugPattern;
import com.google.errorprone.BugPattern.StandardTags;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.ClassTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.google.errorprone.matchers.Matchers;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.Tree;
import com.sun.source.util.TreeScanner;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.ClassSymbol;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.lang.model.element.ElementKind;
/**
* Looks for hashCode implementations which are inconsistent with equals.
*
* @author [email protected] (Graeme Morgan)
*/
@BugPattern(
name = "InconsistentHashCode",
summary =
"Including fields in hashCode which are not compared in equals violates "
+ "the contract of hashCode.",
severity = WARNING,
tags = StandardTags.FRAGILE_CODE)
public final class InconsistentHashCode extends BugChecker implements ClassTreeMatcher {
public static final String MESSAGE =
"hashCode includes the fields %s, which equals does not. Two instances of this class "
+ "could compare equal, but have different hashCodes, which violates the hashCode "
+ "contract.";
/** Non-static methods that we might expect to see in #hashCode, and allow. */
private static final Matcher HASH_CODE_METHODS =
instanceMethod().anyClass().named("hashCode").withNoParameters();
/** Non-static methods that we might expect to see in #equals, and allow. */
private static final Matcher EQUALS_METHODS =
anyOf(instanceMethod().anyClass().named("getClass"), instanceEqualsInvocation());
@Override
public Description matchClass(ClassTree tree, VisitorState state) {
ClassSymbol classSymbol = getSymbol(tree);
MethodTree equalsDeclaration = null;
MethodTree hashCodeDeclaration = null;
for (Tree member : tree.getMembers()) {
if (!(member instanceof MethodTree)) {
continue;
}
MethodTree methodTree = (MethodTree) member;
if (hashCodeMethodDeclaration().matches(methodTree, state)) {
hashCodeDeclaration = methodTree;
} else if (equalsMethodDeclaration().matches(methodTree, state)) {
equalsDeclaration = methodTree;
}
}
if (equalsDeclaration == null || hashCodeDeclaration == null) {
return Description.NO_MATCH;
}
// Build up a map of methods to the fields they access for simple methods, i.e. getters.
// Not a SetMultimap, because we do want to distinguish between "method was not analyzable" and
// "method accessed no fields".
Map> fieldsByMethod = new HashMap<>();
for (Tree member : tree.getMembers()) {
if (!(member instanceof MethodTree)) {
continue;
}
MethodTree methodTree = (MethodTree) member;
if (!methodTree.equals(equalsDeclaration) && !methodTree.equals(hashCodeDeclaration)) {
FieldAccessFinder finder = FieldAccessFinder.scanMethod(state, classSymbol, methodTree);
if (!finder.failed()) {
fieldsByMethod.put(getSymbol(methodTree), finder.accessedFields());
}
}
}
FieldAccessFinder equalsScanner =
FieldAccessFinder.scanMethod(
state, classSymbol, equalsDeclaration, fieldsByMethod, HASH_CODE_METHODS);
FieldAccessFinder hashCodeScanner =
FieldAccessFinder.scanMethod(
state, classSymbol, hashCodeDeclaration, fieldsByMethod, EQUALS_METHODS);
if (equalsScanner.failed() || hashCodeScanner.failed()) {
return Description.NO_MATCH;
}
ImmutableSet fieldsInHashCode = hashCodeScanner.accessedFields();
ImmutableSet fieldsInEquals = equalsScanner.accessedFields();
Set difference = new HashSet<>(Sets.difference(fieldsInHashCode, fieldsInEquals));
// Special-case the situation where #hashCode uses a field containing `hash` for memoization.
difference.removeIf(f -> Ascii.toLowerCase(f.toString()).contains("hash"));
String message = String.format(MESSAGE, difference);
// Skip cases where equals and hashCode compare the same fields, or equals compares none (and
// so is probably checking reference equality).
return difference.isEmpty() || fieldsInEquals.isEmpty()
? Description.NO_MATCH
: buildDescription(hashCodeDeclaration).setMessage(message).build();
}
/**
* Scans a method to find which fields are accessed from it. Fails if instance methods not
* matching {@code acceptableMethods} are found: that is, it's optimised for simple getters.
*/
private static final class FieldAccessFinder extends TreeScanner {
private final Matcher acceptableMethods;
private final Map> knownMethods;
private final ImmutableSet.Builder accessedFields = ImmutableSet.builder();
private final VisitorState state;
private final ClassSymbol classSymbol;
// We bail out if we got any unknown method calls to avoid reporting false positives.
private boolean failed = false;
private static FieldAccessFinder scanMethod(
VisitorState state, ClassSymbol classSymbol, MethodTree methodTree) {
return scanMethod(state, classSymbol, methodTree, ImmutableMap.of(), Matchers.nothing());
}
private static FieldAccessFinder scanMethod(
VisitorState state,
ClassSymbol classSymbol,
MethodTree methodTree,
Map> knownMethods,
Matcher acceptableMethods) {
FieldAccessFinder finder =
new FieldAccessFinder(state, classSymbol, knownMethods, acceptableMethods);
methodTree.accept(finder, null);
return finder;
}
private FieldAccessFinder(
VisitorState state,
ClassSymbol classSymbol,
Map> knownMethods,
Matcher acceptableMethods) {
this.state = state;
this.classSymbol = classSymbol;
this.knownMethods = knownMethods;
this.acceptableMethods = acceptableMethods;
}
@Override
public Void visitMethodInvocation(MethodInvocationTree tree, Void unused) {
MethodSymbol symbol = getSymbol(tree);
if (symbol != null) {
if (knownMethods.containsKey(symbol)) {
accessedFields.addAll(knownMethods.get(symbol));
} else if (!symbol.isStatic() && !acceptableMethods.matches(tree, state)) {
failed = true;
}
}
return super.visitMethodInvocation(tree, null);
}
@Override
public Void visitMemberSelect(MemberSelectTree tree, Void unused) {
ExpressionTree receiver = getReceiver(tree);
ExpressionTree e = tree.getExpression();
if (receiver == null
|| (e instanceof IdentifierTree
&& ((IdentifierTree) e).getName().contentEquals("this"))) {
Symbol symbol = ((JCFieldAccess) tree).sym;
handleSymbol(symbol);
}
return super.visitMemberSelect(tree, null);
}
@Override
public Void visitIdentifier(IdentifierTree tree, Void unused) {
Symbol symbol = getSymbol(tree);
handleSymbol(symbol);
return super.visitIdentifier(tree, null);
}
private void handleSymbol(Symbol symbol) {
if (symbol != null
&& symbol.getKind() == ElementKind.FIELD
&& !symbol.isStatic()
&& symbol.owner.equals(classSymbol)) {
String name = symbol.name.toString();
if (name.equals("this") || name.equals("super")) {
return;
}
accessedFields.add(symbol);
}
}
private ImmutableSet accessedFields() {
return accessedFields.build();
}
public boolean failed() {
return failed;
}
}
}
