/*
* Copyright 2014 Google Inc. All Rights Reserved.
*
* 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.Category.JDK;
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.util.ASTHelpers;
import com.sun.source.tree.MethodTree;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Type.TypeVar;
import com.sun.tools.javac.code.Types;
import java.util.HashSet;
import java.util.Set;
@BugPattern(
name = "TypeParameterUnusedInFormals",
summary =
"Declaring a type parameter that is only used in the return type is a misuse of"
+ " generics: operations on the type parameter are unchecked, it hides unsafe casts at"
+ " invocations of the method, and it interacts badly with method overload resolution.",
category = JDK,
severity = WARNING
)
public class TypeParameterUnusedInFormals extends BugChecker implements MethodTreeMatcher {
@Override
public Description matchMethod(MethodTree tree, VisitorState state) {
MethodSymbol methodSymbol = ASTHelpers.getSymbol(tree);
if (methodSymbol == null) {
return Description.NO_MATCH;
}
// Only match methods where the return type is just a type parameter.
// e.g. the following is OK: <T> List<T> newArrayList();
TypeVar retType;
switch (methodSymbol.getReturnType().getKind()) {
case TYPEVAR:
retType = (TypeVar) methodSymbol.getReturnType();
break;
default:
return Description.NO_MATCH;
}
if (!methodSymbol.equals(retType.tsym.owner)) {
return Description.NO_MATCH;
}
// Ignore f-bounds.
// e.g.: <T extends Enum<T>> T unsafeEnumDeserializer();
if (retType.bound != null && TypeParameterFinder.visit(retType.bound).contains(retType.tsym)) {
return Description.NO_MATCH;
}
// Ignore cases where the type parameter is used in the declaration of a formal parameter.
// e.g.: <T> T noop(T t);
for (VarSymbol formalParam : methodSymbol.getParameters()) {
if (TypeParameterFinder.visit(formalParam.type).contains(retType.tsym)) {
return Description.NO_MATCH;
}
}
return describeMatch(tree);
}
/**
* A visitor that records the set of {@link com.sun.tools.javac.code.Type.TypeVar}s referenced by
* the current type.
*/
private static class TypeParameterFinder extends Types.DefaultTypeVisitor<Void, Void> {
static Set<Symbol.TypeSymbol> visit(Type type) {
TypeParameterFinder visitor = new TypeParameterFinder();
type.accept(visitor, null);
return visitor.seen;
}
private final Set<Symbol.TypeSymbol> seen = new HashSet<>();
@Override
public Void visitClassType(Type.ClassType type, Void unused) {
if (type instanceof Type.IntersectionClassType) {
// TypeVisitor doesn't support intersection types natively
visitIntersectionClassType((Type.IntersectionClassType) type);
} else {
for (Type t : type.getTypeArguments()) {
t.accept(this, null);
}
}
return null;
}
public void visitIntersectionClassType(Type.IntersectionClassType type) {
for (Type component : type.getComponents()) {
component.accept(this, null);
}
}
@Override
public Void visitWildcardType(Type.WildcardType type, Void unused) {
if (type.getSuperBound() != null) {
type.getSuperBound().accept(this, null);
}
if (type.getExtendsBound() != null) {
type.getExtendsBound().accept(this, null);
}
return null;
}
@Override
public Void visitArrayType(Type.ArrayType type, Void unused) {
type.elemtype.accept(this, null);
return null;
}
@Override
public Void visitTypeVar(Type.TypeVar type, Void unused) {
// only visit f-bounds once:
if (!seen.add(type.tsym)) {
return null;
}
if (type.bound != null) {
type.bound.accept(this, null);
}
return null;
}
@Override
public Void visitType(Type type, Void unused) {
return null;
}
}
}