| // Copyright 2014 The Bazel Authors. 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.devtools.common.options; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| import com.google.common.primitives.Primitives; |
| import com.google.common.reflect.TypeToken; |
| |
| import java.lang.reflect.Method; |
| import java.lang.reflect.ParameterizedType; |
| import java.lang.reflect.Type; |
| import java.lang.reflect.TypeVariable; |
| |
| /** |
| * A helper class for {@link OptionsParserImpl} to help checking the return type |
| * of a {@link Converter} against the type of a field or the element type of a |
| * list. |
| * |
| * <p>This class has to go through considerable contortion to get the correct result |
| * from the Java reflection system, unfortunately. If the generic reflection part |
| * had been better designed, some of this would not be necessary. |
| */ |
| class GenericTypeHelper { |
| |
| /** |
| * Returns the raw type of t, if t is either a raw or parameterized type. |
| * Otherwise, this method throws an {@link AssertionError}. |
| */ |
| @VisibleForTesting |
| static Class<?> getRawType(Type t) { |
| if (t instanceof Class<?>) { |
| return (Class<?>) t; |
| } else if (t instanceof ParameterizedType) { |
| return (Class<?>) ((ParameterizedType) t).getRawType(); |
| } else { |
| throw new AssertionError("A known concrete type is not concrete"); |
| } |
| } |
| |
| /** |
| * If type is a parameterized type, searches the given type variable in the list |
| * of declared type variables, and then returns the corresponding actual type. |
| * Returns null if the type variable is not defined by type. |
| */ |
| private static Type matchTypeVariable(Type type, TypeVariable<?> variable) { |
| if (type instanceof ParameterizedType) { |
| Class<?> rawInterfaceType = getRawType(type); |
| TypeVariable<?>[] typeParameters = rawInterfaceType.getTypeParameters(); |
| for (int i = 0; i < typeParameters.length; i++) { |
| if (variable.equals(typeParameters[i])) { |
| return ((ParameterizedType) type).getActualTypeArguments()[i]; |
| } |
| } |
| } |
| return null; |
| } |
| |
| /** |
| * Resolves the return type of a method, in particular if the generic return |
| * type ({@link Method#getGenericReturnType()}) is a type variable |
| * ({@link TypeVariable}), by checking all super-classes and directly |
| * implemented interfaces. |
| * |
| * <p>The method m must be defined by the given type or by its raw class type. |
| * |
| * @throws AssertionError if the generic return type could not be resolved |
| */ |
| // TODO(bazel-team): also check enclosing classes and indirectly implemented |
| // interfaces, which can also contribute type variables. This doesn't happen |
| // in the existing use cases. |
| public static Type getActualReturnType(Type type, Method method) { |
| Type returnType = method.getGenericReturnType(); |
| if (returnType instanceof Class<?>) { |
| return returnType; |
| } else if (returnType instanceof ParameterizedType) { |
| return returnType; |
| } else if (returnType instanceof TypeVariable<?>) { |
| TypeVariable<?> variable = (TypeVariable<?>) returnType; |
| while (type != null) { |
| Type candidate = matchTypeVariable(type, variable); |
| if (candidate != null) { |
| return candidate; |
| } |
| |
| Class<?> rawType = getRawType(type); |
| for (Type interfaceType : rawType.getGenericInterfaces()) { |
| candidate = matchTypeVariable(interfaceType, variable); |
| if (candidate != null) { |
| return candidate; |
| } |
| } |
| |
| type = rawType.getGenericSuperclass(); |
| } |
| } |
| throw new AssertionError("The type " + returnType |
| + " is not a Class, ParameterizedType, or TypeVariable"); |
| } |
| |
| /** |
| * Determines if a value of a particular type (from) is assignable to a field of |
| * a particular type (to). Also allows assigning wrapper types to primitive |
| * types. |
| * |
| * <p>The checks done here should be identical to the checks done by |
| * {@link java.lang.reflect.Field#set}. I.e., if this method returns true, a |
| * subsequent call to {@link java.lang.reflect.Field#set} should succeed. |
| */ |
| public static boolean isAssignableFrom(Type to, Type from) { |
| if (to instanceof Class<?>) { |
| Class<?> toClass = (Class<?>) to; |
| if (toClass.isPrimitive()) { |
| return Primitives.wrap(toClass).equals(from); |
| } |
| } |
| return TypeToken.of(to).isSupertypeOf(from); |
| } |
| |
| private GenericTypeHelper() { |
| // Prevents Java from creating a public constructor. |
| } |
| } |