core/src/com/google/inject/internal/ProviderMethodsModule.java

/*
 * Copyright (C) 2008 Google Inc.
 *
 * 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.inject.internal;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;
import com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provides;
import com.google.inject.TypeLiteral;
import com.google.inject.spi.InjectionPoint;
import com.google.inject.spi.Message;
import com.google.inject.spi.ModuleAnnotatedMethodScanner;
import com.google.inject.util.Modules;
import java.lang.annotation.Annotation;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;
import java.util.List;

/**
 * Creates bindings to methods annotated with {@literal @}{@link Provides}. Use the scope and
 * binding annotations on the provider method to configure the binding.
 *
 * @author crazybob@google.com (Bob Lee)
 * @author jessewilson@google.com (Jesse Wilson)
 */
public final class ProviderMethodsModule implements Module {
  private final Object delegate;
  private final TypeLiteral<?> typeLiteral;
  private final boolean skipFastClassGeneration;
  private final ModuleAnnotatedMethodScanner scanner;

  private ProviderMethodsModule(
      Object delegate, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
    this.delegate = checkNotNull(delegate, "delegate");
    this.typeLiteral = TypeLiteral.get(this.delegate.getClass());
    this.skipFastClassGeneration = skipFastClassGeneration;
    this.scanner = scanner;
  }

  /** Returns a module which creates bindings for provider methods from the given module. */
  public static Module forModule(Module module) {
    return forObject(module, false, ProvidesMethodScanner.INSTANCE);
  }

  /** Returns a module which creates bindings methods in the module that match the scanner. */
  public static Module forModule(Object module, ModuleAnnotatedMethodScanner scanner) {
    return forObject(module, false, scanner);
  }

  /**
   * Returns a module which creates bindings for provider methods from the given object. This is
   * useful notably for <a href="http://code.google.com/p/google-gin/">GIN</a>
   *
   * <p>This will skip bytecode generation for provider methods, since it is assumed that callers
   * are only interested in Module metadata.
   */
  public static Module forObject(Object object) {
    return forObject(object, true, ProvidesMethodScanner.INSTANCE);
  }

  private static Module forObject(
      Object object, boolean skipFastClassGeneration, ModuleAnnotatedMethodScanner scanner) {
    // avoid infinite recursion, since installing a module always installs itself
    if (object instanceof ProviderMethodsModule) {
      return Modules.EMPTY_MODULE;
    }

    return new ProviderMethodsModule(object, skipFastClassGeneration, scanner);
  }

  public Object getDelegateModule() {
    return delegate;
  }

  @Override
  public void configure(Binder binder) {
    for (ProviderMethod<?> providerMethod : getProviderMethods(binder)) {
      providerMethod.configure(binder);
    }
  }

  public List<ProviderMethod<?>> getProviderMethods(Binder binder) {
    List<ProviderMethod<?>> result = null;
    // The highest class in the type hierarchy that contained a provider method definition.
    Class<?> superMostClass = delegate.getClass();
    for (Class<?> c = delegate.getClass(); c != Object.class; c = c.getSuperclass()) {
      for (Method method : c.getDeclaredMethods()) {
        Annotation annotation = getAnnotation(binder, method);
        if (annotation != null) {
          if (result == null) {
            result = Lists.newArrayList();
          }
          result.add(createProviderMethod(binder, method, annotation));
          superMostClass = c;
        }
      }
    }
    if (result == null) {
      // We didn't find anything
      return ImmutableList.of();
    }
    // We have found some provider methods, now we need to check if any were overridden.
    // We do this as a separate pass to avoid calculating all the signatures when there are no
    // provides methods, or when all provides methods are defined in a single class.
    Multimap<Signature, Method> methodsBySignature = null;
    // We can stop scanning when we see superMostClass, since no superclass method can override
    // a method in a subclass.  Corrollary, if superMostClass == delegate.getClass(), there can be
    // no overrides of a provides method.
    for (Class<?> c = delegate.getClass(); c != superMostClass; c = c.getSuperclass()) {
      for (Method method : c.getDeclaredMethods()) {
        if (((method.getModifiers() & (Modifier.PRIVATE | Modifier.STATIC)) == 0)
            && !method.isBridge()
            && !method.isSynthetic()) {
          if (methodsBySignature == null) {
            methodsBySignature = HashMultimap.create();
          }
          methodsBySignature.put(new Signature(typeLiteral, method), method);
        }
      }
    }
    if (methodsBySignature != null) {
      // we have found all the signatures and now need to identify if any were overridden
      // In the worst case this will have O(n^2) in the number of @Provides methods, but that is
      // only assuming that every method is an override, in general it should be very quick.
      for (ProviderMethod<?> provider : result) {
        Method method = provider.getMethod();
        for (Method matchingSignature :
            methodsBySignature.get(new Signature(typeLiteral, method))) {
          // matching signature is in the same class or a super class, therefore method cannot be
          // overridding it.
          if (matchingSignature.getDeclaringClass().isAssignableFrom(method.getDeclaringClass())) {
            continue;
          }
          // now we know matching signature is in a subtype of method.getDeclaringClass()
          if (overrides(matchingSignature, method)) {
            String annotationString =
                provider.getAnnotation().annotationType() == Provides.class
                    ? "@Provides"
                    : "@" + provider.getAnnotation().annotationType().getCanonicalName();
            binder.addError(
                "Overriding "
                    + annotationString
                    + " methods is not allowed."
                    + "\n\t"
                    + annotationString
                    + " method: %s\n\toverridden by: %s",
                method,
                matchingSignature);
            break;
          }
        }
      }
    }
    return result;
  }

  /** Returns the annotation that is claimed by the scanner, or null if there is none. */
  private Annotation getAnnotation(Binder binder, Method method) {
    if (method.isBridge() || method.isSynthetic()) {
      return null;
    }
    Annotation annotation = null;
    for (Class<? extends Annotation> annotationClass : scanner.annotationClasses()) {
      Annotation foundAnnotation = method.getAnnotation(annotationClass);
      if (foundAnnotation != null) {
        if (annotation != null) {
          binder.addError(
              "More than one annotation claimed by %s on method %s."
                  + " Methods can only have one annotation claimed per scanner.",
              scanner, method);
          return null;
        }
        annotation = foundAnnotation;
      }
    }
    return annotation;
  }

  private static final class Signature {
    final Class<?>[] parameters;
    final String name;
    final int hashCode;

    Signature(TypeLiteral<?> typeLiteral, Method method) {
      this.name = method.getName();
      // We need to 'resolve' the parameters against the actual class type in case this method uses
      // type parameters.  This is so we can detect overrides of generic superclass methods where
      // the subclass specifies the type parameter.  javac implements these kinds of overrides via
      // bridge methods, but we don't want to give errors on bridge methods (but rather the target
      // of the bridge).
      List<TypeLiteral<?>> resolvedParameterTypes = typeLiteral.getParameterTypes(method);
      this.parameters = new Class<?>[resolvedParameterTypes.size()];
      int i = 0;
      for (TypeLiteral<?> type : resolvedParameterTypes) {
        parameters[i] = type.getRawType();
      }
      this.hashCode = name.hashCode() + 31 * Arrays.hashCode(parameters);
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof Signature) {
        Signature other = (Signature) obj;
        return other.name.equals(name) && Arrays.equals(parameters, other.parameters);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return hashCode;
    }
  }

  /** Returns true if a overrides b, assumes that the signatures match */
  private static boolean overrides(Method a, Method b) {
    // See JLS section 8.4.8.1
    int modifiers = b.getModifiers();
    if (Modifier.isPublic(modifiers) || Modifier.isProtected(modifiers)) {
      return true;
    }
    if (Modifier.isPrivate(modifiers)) {
      return false;
    }
    // b must be package-private
    return a.getDeclaringClass().getPackage().equals(b.getDeclaringClass().getPackage());
  }

  private <T> ProviderMethod<T> createProviderMethod(
      Binder binder, Method method, Annotation annotation) {
    binder = binder.withSource(method);
    Errors errors = new Errors(method);

    // prepare the parameter providers
    InjectionPoint point = InjectionPoint.forMethod(method, typeLiteral);
    @SuppressWarnings("unchecked") // Define T as the method's return type.
    TypeLiteral<T> returnType = (TypeLiteral<T>) typeLiteral.getReturnType(method);
    Key<T> key = getKey(errors, returnType, method, method.getAnnotations());
    try {
      key = scanner.prepareMethod(binder, annotation, key, point);
    } catch (Throwable t) {
      binder.addError(t);
    }
    Class<? extends Annotation> scopeAnnotation =
        Annotations.findScopeAnnotation(errors, method.getAnnotations());
    for (Message message : errors.getMessages()) {
      binder.addError(message);
    }
    return ProviderMethod.create(
        key,
        method,
        delegate,
        ImmutableSet.copyOf(point.getDependencies()),
        scopeAnnotation,
        skipFastClassGeneration,
        annotation);
  }

  <T> Key<T> getKey(Errors errors, TypeLiteral<T> type, Member member, Annotation[] annotations) {
    Annotation bindingAnnotation = Annotations.findBindingAnnotation(errors, member, annotations);
    return bindingAnnotation == null ? Key.get(type) : Key.get(type, bindingAnnotation);
  }

  @Override
  public boolean equals(Object o) {
    return o instanceof ProviderMethodsModule
        && ((ProviderMethodsModule) o).delegate == delegate
        && ((ProviderMethodsModule) o).scanner == scanner;
  }

  @Override
  public int hashCode() {
    return delegate.hashCode();
  }
}