1 /* 2 * Copyright 2014 Google LLC 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package com.google.auto.value.processor; 17 18 import java.util.List; 19 import javax.lang.model.element.ExecutableElement; 20 import javax.lang.model.element.VariableElement; 21 import javax.lang.model.type.ArrayType; 22 import javax.lang.model.type.DeclaredType; 23 import javax.lang.model.type.ErrorType; 24 import javax.lang.model.type.IntersectionType; 25 import javax.lang.model.type.TypeMirror; 26 import javax.lang.model.type.TypeVariable; 27 import javax.lang.model.type.WildcardType; 28 import javax.lang.model.util.SimpleTypeVisitor8; 29 30 /** 31 * Handling of undefined types. When we see an undefined type, it might genuinely be undefined, or 32 * it might be a type whose source code will be generated later on as part of the same compilation. 33 * If we encounter an undefined type in a place where we need to know the type, we throw {@link 34 * MissingTypeException}. We then catch that and defer processing for the current class until the 35 * next annotation-processing "round". If the missing class has been generated in the meanwhile, we 36 * may now be able to complete processing. After a round has completed without generating any new 37 * source code, if there are still missing types then we report an error. 38 * 39 * @author emcmanus@google.com (Éamonn McManus) 40 */ 41 final class MissingTypes { MissingTypes()42 private MissingTypes() {} 43 44 /** 45 * Exception thrown in the specific case where processing of a class was abandoned because it 46 * required types that the class references to be present and they were not. This case is handled 47 * specially because it is possible that those types might be generated later during annotation 48 * processing, so we should reattempt the processing of the class in a later annotation processing 49 * round. 50 */ 51 @SuppressWarnings("serial") 52 static class MissingTypeException extends RuntimeException { MissingTypeException(ErrorType missingType)53 MissingTypeException(ErrorType missingType) { 54 // Although it is not specified as such, in practice ErrorType.toString() is the type name 55 // that appeared in the source code. Showing it here can help in debugging issues with 56 // deferral. 57 super(missingType == null ? null : missingType.toString()); 58 } 59 } 60 61 /** 62 * Check that the return type and parameter types of the given method are all defined, and arrange 63 * to defer processing until the next round if not. 64 * 65 * @throws MissingTypeException if the return type or a parameter type of the given method is 66 * undefined 67 */ deferIfMissingTypesIn(ExecutableElement method)68 static void deferIfMissingTypesIn(ExecutableElement method) { 69 MISSING_TYPE_VISITOR.check(method.getReturnType()); 70 for (VariableElement param : method.getParameters()) { 71 MISSING_TYPE_VISITOR.check(param.asType()); 72 } 73 } 74 75 private static final MissingTypeVisitor MISSING_TYPE_VISITOR = new MissingTypeVisitor(); 76 77 private static class MissingTypeVisitor extends SimpleTypeVisitor8<Void, TypeMirrorSet> { 78 // Avoid infinite recursion for a type like `Enum<E extends Enum<E>>` by remembering types that 79 // we have already seen on this visit. Recursion has to go through a declared type, such as Enum 80 // in this example, so in principle it should be enough to check only in visitDeclared. However 81 // Eclipse has a quirk where the second E in `Enum<E extends Enum<E>>` is not the same as the 82 // first, and if you ask for its bounds you will get another `Enum<E>` with a third E. So we 83 // also check in visitTypeVariable. TypeMirrorSet does consider that all these E variables are 84 // the same so infinite recursion is avoided. check(TypeMirror type)85 void check(TypeMirror type) { 86 type.accept(this, new TypeMirrorSet()); 87 } 88 89 @Override visitError(ErrorType t, TypeMirrorSet visiting)90 public Void visitError(ErrorType t, TypeMirrorSet visiting) { 91 throw new MissingTypeException(t); 92 } 93 94 @Override visitArray(ArrayType t, TypeMirrorSet visiting)95 public Void visitArray(ArrayType t, TypeMirrorSet visiting) { 96 return t.getComponentType().accept(this, visiting); 97 } 98 99 @Override visitDeclared(DeclaredType t, TypeMirrorSet visiting)100 public Void visitDeclared(DeclaredType t, TypeMirrorSet visiting) { 101 if (visiting.add(t)) { 102 visitAll(t.getTypeArguments(), visiting); 103 } 104 return null; 105 } 106 107 @Override visitTypeVariable(TypeVariable t, TypeMirrorSet visiting)108 public Void visitTypeVariable(TypeVariable t, TypeMirrorSet visiting) { 109 if (visiting.add(t)) { 110 t.getLowerBound().accept(this, visiting); 111 t.getUpperBound().accept(this, visiting); 112 } 113 return null; 114 } 115 116 @Override visitWildcard(WildcardType t, TypeMirrorSet visiting)117 public Void visitWildcard(WildcardType t, TypeMirrorSet visiting) { 118 if (t.getSuperBound() != null) { 119 t.getSuperBound().accept(this, visiting); 120 } 121 if (t.getExtendsBound() != null) { 122 t.getExtendsBound().accept(this, visiting); 123 } 124 return null; 125 } 126 127 @Override visitIntersection(IntersectionType t, TypeMirrorSet visiting)128 public Void visitIntersection(IntersectionType t, TypeMirrorSet visiting) { 129 return visitAll(t.getBounds(), visiting); 130 } 131 visitAll(List<? extends TypeMirror> types, TypeMirrorSet visiting)132 private Void visitAll(List<? extends TypeMirror> types, TypeMirrorSet visiting) { 133 for (TypeMirror type : types) { 134 type.accept(this, visiting); 135 } 136 return null; 137 } 138 } 139 } 140