src/main/java/com/google/devtools/build/lib/packages/AspectDefinition.java - bazel - Git at Google

 // 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.build.lib.packages;

 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableMultimap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.LinkedHashMultimap;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.SetMultimap;
 import com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransition;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.packages.ConfigurationFragmentPolicy.MissingFragmentPolicy;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.syntax.Type.LabelClass;
 import com.google.devtools.build.lib.syntax.Type.LabelVisitor;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import javax.annotation.Nullable;

 /**
  * The definition of an aspect (see {@link Aspect} for more information).
  *
  * <p>Contains enough information to build up the configured target graph except for the actual way
  * to build the Skyframe node (that is the territory of {@link com.google.devtools.build.lib.view
  * AspectFactory}). In particular:
  *
  * <ul>
  *   <li>The condition that must be fulfilled for an aspect to be able to operate on a configured
  *       target
  *   <li>The (implicit or late-bound) attributes of the aspect that denote dependencies the aspect
  *       itself needs (e.g. runtime libraries for a new language for protocol buffers)
  *   <li>The aspects this aspect requires from its direct dependencies
  * </ul>
  *
  * <p>The way to build the Skyframe node is not here because this data needs to be accessible from
  * the {@code .packages} package and that one requires references to the {@code .view} package.
  */
 @AutoCodec
 @Immutable
 public final class AspectDefinition {
   private final AspectClass aspectClass;
   private final AdvertisedProviderSet advertisedProviders;
   private final RequiredProviders requiredProviders;
   private final RequiredProviders requiredProvidersForAspects;
   private final ImmutableMap<String, Attribute> attributes;
   private final ImmutableSet<Label> requiredToolchains;

   /**
    * Which attributes aspect should propagate along:
    * <ul>
    *  <li>A {@code null} value means propagate along all attributes</li>
    *  <li>A (possibly empty) set means to propagate only along the attributes in a set</li>
    * </ul>
    */
   @Nullable private final ImmutableSet<String> restrictToAttributes;
   @Nullable private final ConfigurationFragmentPolicy configurationFragmentPolicy;
   private final boolean applyToFiles;

   public AdvertisedProviderSet getAdvertisedProviders() {
     return advertisedProviders;
   }

   @AutoCodec.VisibleForSerialization
   AspectDefinition(
       AspectClass aspectClass,
       AdvertisedProviderSet advertisedProviders,
       RequiredProviders requiredProviders,
       RequiredProviders requiredProvidersForAspects,
       ImmutableMap<String, Attribute> attributes,
       ImmutableSet<Label> requiredToolchains,
       @Nullable ImmutableSet<String> restrictToAttributes,
       @Nullable ConfigurationFragmentPolicy configurationFragmentPolicy,
       boolean applyToFiles) {
     this.aspectClass = aspectClass;
     this.advertisedProviders = advertisedProviders;
     this.requiredProviders = requiredProviders;
     this.requiredProvidersForAspects = requiredProvidersForAspects;

     this.attributes = attributes;
     this.requiredToolchains = requiredToolchains;
     this.restrictToAttributes = restrictToAttributes;
     this.configurationFragmentPolicy = configurationFragmentPolicy;
     this.applyToFiles = applyToFiles;
   }

   public String getName() {
     return aspectClass.getName();
   }

   public AspectClass getAspectClass() {
     return aspectClass;
   }

   /**
    * Returns the attributes of the aspect in the form of a String -&gt; {@link Attribute} map.
    *
    * <p>All attributes are either implicit or late-bound.
    */
   public ImmutableMap<String, Attribute> getAttributes() {
     return attributes;
   }

   /** Returns the required toolchains declared by this aspect. */
   public ImmutableSet<Label> getRequiredToolchains() {
     return requiredToolchains;
   }

   /**
    * Returns {@link RequiredProviders} that a configured target must have so that
    * this aspect can be applied to it.
    *
    * <p>If a configured target does not satisfy required providers, the aspect is
    * silently not created for it.
    */
   public RequiredProviders getRequiredProviders() {
     return requiredProviders;
   }

   /**
    * Aspects do not depend on other aspects applied to the same target <em>unless</em>
    * the other aspect satisfies the {@link RequiredProviders} this method returns
    */
   public RequiredProviders getRequiredProvidersForAspects() {
     return requiredProvidersForAspects;
   }

   /** Returns the set of required aspects for a given attribute. */
   public boolean propagateAlong(String attributeName) {
     if (restrictToAttributes != null) {
       return restrictToAttributes.contains(attributeName);
     }
     return true;
   }

   /**
    * Returns the set of configuration fragments required by this Aspect.
    */
   public ConfigurationFragmentPolicy getConfigurationFragmentPolicy() {
     return configurationFragmentPolicy;
   }

   /**
    * Returns whether this aspect applies to (output) files.
    *
    * Currently only supported for top-level aspects and targets, and
    * only for output files.
    */
   public boolean applyToFiles() {
     return applyToFiles;
   }

   /**
    * Returns the attribute -&gt; set of labels that are provided by aspects of attribute.
    */
   public static ImmutableMultimap<Attribute, Label> visitAspectsIfRequired(
       Target from, Attribute attribute, Target to,
       DependencyFilter dependencyFilter) {
     // Aspect can be declared only for Rules.
     if (!(from instanceof Rule) || !(to instanceof Rule)) {
       return ImmutableMultimap.of();
     }
     RuleClass ruleClass = ((Rule) to).getRuleClassObject();
     AdvertisedProviderSet providers = ruleClass.getAdvertisedProviders();
     return visitAspectsIfRequired((Rule) from, attribute,
         providers, dependencyFilter);
   }

   /**
    * Returns the attribute -&gt; set of labels that are provided by aspects of attribute.
    */
   public static ImmutableMultimap<Attribute, Label> visitAspectsIfRequired(
       Rule from, Attribute attribute,
       AdvertisedProviderSet advertisedProviders,
       DependencyFilter dependencyFilter) {
     SetMultimap<Attribute, Label> result = LinkedHashMultimap.create();
     for (Aspect candidateClass : attribute.getAspects(from)) {
       // Check if target satisfies condition for this aspect (has to provide all required
       // TransitiveInfoProviders)
       RequiredProviders requiredProviders =
           candidateClass.getDefinition().getRequiredProviders();
       if (requiredProviders.isSatisfiedBy(advertisedProviders)) {
         addAllAttributesOfAspect(from, result, candidateClass, dependencyFilter);
       }
     }
     return ImmutableMultimap.copyOf(result);
   }

   @Nullable
   private static Label maybeGetRepositoryRelativeLabel(Rule from, @Nullable Label label) {
     return label == null ? null : from.getLabel().resolveRepositoryRelative(label);
   }

   /**
    * Collects all attribute labels from the specified aspectDefinition.
    */
   public static void addAllAttributesOfAspect(
       final Rule from,
       final Multimap<Attribute, Label> labelBuilder,
       Aspect aspect,
       DependencyFilter dependencyFilter) {
     LabelVisitor<Attribute> labelVisitor =
         (label, aspectAttribute) -> {
           Label repositoryRelative = maybeGetRepositoryRelativeLabel(from, label);
           if (repositoryRelative == null) {
             return;
           }
           labelBuilder.put(aspectAttribute, repositoryRelative);
         };
     ImmutableMap<String, Attribute> attributes = aspect.getDefinition().getAttributes();
     for (final Attribute aspectAttribute : attributes.values()) {
       if (!dependencyFilter.apply(aspect, aspectAttribute)) {
         continue;
       }
       Type<?> type = aspectAttribute.getType();
       if (type.getLabelClass() != LabelClass.DEPENDENCY) {
         continue;
       }
       type.visitLabels(labelVisitor, aspectAttribute.getDefaultValue(from), aspectAttribute);
     }
   }

   public static Builder builder(AspectClass aspectClass) {
     return new Builder(aspectClass);
   }

   /**
    * Builder class for {@link AspectDefinition}.
    */
   public static final class Builder {
     private final AspectClass aspectClass;
     private final Map<String, Attribute> attributes = new LinkedHashMap<>();
     private final AdvertisedProviderSet.Builder advertisedProviders =
         AdvertisedProviderSet.builder();
     private RequiredProviders.Builder requiredProviders = RequiredProviders.acceptAnyBuilder();
     private RequiredProviders.Builder requiredAspectProviders =
         RequiredProviders.acceptNoneBuilder();
     @Nullable
     private LinkedHashSet<String> propagateAlongAttributes = new LinkedHashSet<>();
     private final ConfigurationFragmentPolicy.Builder configurationFragmentPolicy =
         new ConfigurationFragmentPolicy.Builder();
     private boolean applyToFiles = false;
     private final List<Label> requiredToolchains = new ArrayList<>();

     public Builder(AspectClass aspectClass) {
       this.aspectClass = aspectClass;
     }

     /**
      * Asserts that this aspect can only be evaluated for rules that supply all of the providers
      * from at least one set of required providers.
      */
     public Builder requireProviderSets(Iterable<ImmutableSet<Class<?>>> providerSets) {
       for (ImmutableSet<Class<?>> providerSet : providerSets) {
         requiredProviders.addNativeSet(providerSet);
       }
       return this;
     }

     /**
      * Asserts that this aspect can only be evaluated for rules that supply all of the specified
      * providers.
      */
     public Builder requireProviders(Class<?>... providers) {
       requiredProviders.addNativeSet(ImmutableSet.copyOf(providers));
       return this;
     }

     /**
      * Asserts that this aspect can only be evaluated for rules that supply all of the specified
      * Skylark providers.
      */
     public Builder requireSkylarkProviders(SkylarkProviderIdentifier... skylarkProviders) {
       requiredProviders.addSkylarkSet(ImmutableSet.copyOf(skylarkProviders));
       return this;
     }

     public Builder requireAspectsWithProviders(
         Iterable<ImmutableSet<SkylarkProviderIdentifier>> providerSets) {
       for (ImmutableSet<SkylarkProviderIdentifier> providerSet : providerSets) {
         if (!providerSet.isEmpty()) {
           requiredAspectProviders.addSkylarkSet(providerSet);
         }
       }
       return this;
     }

     public Builder requireAspectsWithNativeProviders(
         Class<?>... providers) {
       requiredAspectProviders.addNativeSet(ImmutableSet.copyOf(providers));
       return this;
     }

     /**
      * State that the aspect being built provides given providers.
      */
     public Builder advertiseProvider(Class<?>... providers) {
       for (Class<?> provider : providers) {
         advertisedProviders.addNative(provider);
       }
       return this;
     }

     /**
      * State that the aspect being built provides given providers.
      */
     public Builder advertiseProvider(ImmutableList<SkylarkProviderIdentifier> providers) {
       for (SkylarkProviderIdentifier provider : providers) {
         advertisedProviders.addSkylark(provider);
       }
       return this;
     }


     /**
      * Declares that this aspect propagates along an {@code attribute} on the target
      * associated with this aspect.
      *
      * Specify multiple attributes by calling {@link #propagateAlongAttribute(String)}
      * repeatedly.
      *
      * Aspect can also declare to propagate along all attributes with
      * {@link #propagateAlongAttributes}.
      */
     public final Builder propagateAlongAttribute(String attribute) {
       Preconditions.checkNotNull(attribute);
       Preconditions.checkState(this.propagateAlongAttributes != null,
           "Either propagate along all attributes, or along specific attributes, not both");

       this.propagateAlongAttributes.add(attribute);

       return this;
     }

     /**
      * Declares that this aspect propagates along all attributes on the target
      * associated with this aspect.
      *
      * Specify either this or {@link #propagateAlongAttribute(String)}, not both.
      */
     public final Builder propagateAlongAllAttributes() {
       Preconditions.checkState(this.propagateAlongAttributes != null,
           "Aspects for all attributes must only be specified once");

       Preconditions.checkState(this.propagateAlongAttributes.isEmpty(),
           "Specify either aspects for all attributes, or for specific attributes, not both");
       this.propagateAlongAttributes = null;
       return this;
     }

     /**
      * Adds an attribute to the aspect.
      *
      * <p>Since aspects do not appear in BUILD files, the attribute must be either implicit
      * (not available in the BUILD file, starting with '$') or late-bound (determined after the
      * configuration is available, starting with ':')
      */
     public <TYPE> Builder add(Attribute.Builder<TYPE> attr) {
       Attribute attribute = attr.build();
       return add(attribute);
     }

     /**
      * Adds an attribute to the aspect.
      *
      * <p>Since aspects do not appear in BUILD files, the attribute must be either implicit
      * (not available in the BUILD file, starting with '$') or late-bound (determined after the
      * configuration is available, starting with ':')
      */
     public Builder add(Attribute attribute) {
       Preconditions.checkArgument(attribute.isImplicit() || attribute.isLateBound()
           || (attribute.getType() == Type.STRING && attribute.checkAllowedValues()),
           "Invalid attribute '%s' (%s)", attribute.getName(), attribute.getType());
       Preconditions.checkArgument(!attributes.containsKey(attribute.getName()),
           "An attribute with the name '%s' already exists.", attribute.getName());
       attributes.put(attribute.getName(), attribute);
       return this;
     }

     /**
      * Declares that the implementation of the associated aspect definition requires the given
      * fragments to be present in this rule's host and target configurations.
      *
      * <p>The value is inherited by subclasses.
      */
     public Builder requiresConfigurationFragments(Class<?>... configurationFragments) {
       configurationFragmentPolicy
           .requiresConfigurationFragments(ImmutableSet.copyOf(configurationFragments));
       return this;
     }

     /**
      * Declares that the implementation of the associated aspect definition requires the given
      * fragments to be present in the given configuration that isn't the aspect's configuration but
      * is also readable by the aspect.
      *
      * <p>You probably don't want to use this, because aspects generally shouldn't read
      * configurations other than their own. If you want to declare host config fragments, see
      * {@link com.google.devtools.build.lib.analysis.config.ConfigAwareAspectBuilder}.
      *
      * <p>The value is inherited by subclasses.
      */
     public Builder requiresConfigurationFragments(ConfigurationTransition transition,
         Class<?>... configurationFragments) {
       configurationFragmentPolicy.requiresConfigurationFragments(transition,
           ImmutableSet.copyOf(configurationFragments));
       return this;
     }

     /**
      * Declares the configuration fragments that are required by this rule for the target
      * configuration.
      *
      * <p>In contrast to {@link #requiresConfigurationFragments(Class...)}, this method takes the
      * Skylark module names of fragments instead of their classes.
      */
     public Builder requiresConfigurationFragmentsBySkylarkModuleName(
         Collection<String> configurationFragmentNames) {
       configurationFragmentPolicy
           .requiresConfigurationFragmentsBySkylarkModuleName(configurationFragmentNames);
       return this;
     }

     /**
      * Declares that the implementation of the associated aspect definition requires the given
      * fragments to be present in the given configuration that isn't the aspect's configuration but
      * is also readable by the aspect.
      *
      * <p>In contrast to {@link #requiresConfigurationFragments(ConfigurationTransition, Class...)},
      * this method takes the Skylark module names of fragments instead of their classes.
      *
      * <p>You probably don't want to use this, because aspects generally shouldn't read
      * configurations other than their own. If you want to declare host config fragments, see
      * {@link com.google.devtools.build.lib.analysis.config.ConfigAwareAspectBuilder}.
      */
     public Builder requiresConfigurationFragmentsBySkylarkModuleName(
         ConfigurationTransition transition, Collection<String> configurationFragmentNames) {
       configurationFragmentPolicy.requiresConfigurationFragmentsBySkylarkModuleName(transition,
           configurationFragmentNames);
       return this;
     }

     /**
      * Sets the policy for the case where the configuration is missing required fragments (see
      * {@link #requiresConfigurationFragments}).
      */
     public Builder setMissingFragmentPolicy(MissingFragmentPolicy missingFragmentPolicy) {
       configurationFragmentPolicy.setMissingFragmentPolicy(missingFragmentPolicy);
       return this;
     }

     /**
      * Sets whether this aspect should apply to files.
      *
      * Default is <code>false</code>.
      * Currently only supported for top-level aspects and targets, and only for
      * output files.
      */
     public Builder applyToFiles(boolean propagateOverGeneratedFiles) {
       this.applyToFiles = propagateOverGeneratedFiles;
       return this;
     }

     /** Adds the given toolchains as requirements for this aspect. */
     public Builder addRequiredToolchains(Label... toolchainLabels) {
       Iterables.addAll(this.requiredToolchains, Lists.newArrayList(toolchainLabels));
       return this;
     }

     /** Adds the given toolchains as requirements for this aspect. */
     public Builder addRequiredToolchains(List<Label> requiredToolchains) {
       this.requiredToolchains.addAll(requiredToolchains);
       return this;
     }
     /**
      * Builds the aspect definition.
      *
      * <p>The builder object is reusable afterwards.
      */
     public AspectDefinition build() {
       return new AspectDefinition(
           aspectClass,
           advertisedProviders.build(),
           requiredProviders.build(),
           requiredAspectProviders.build(),
           ImmutableMap.copyOf(attributes),
           ImmutableSet.copyOf(requiredToolchains),
           propagateAlongAttributes == null ? null : ImmutableSet.copyOf(propagateAlongAttributes),
           configurationFragmentPolicy.build(),
           applyToFiles);
     }
   }
 }
	// 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.build.lib.packages;

	import com.google.common.base.Preconditions;
	import com.google.common.collect.ImmutableList;
	import com.google.common.collect.ImmutableMap;
	import com.google.common.collect.ImmutableMultimap;
	import com.google.common.collect.ImmutableSet;
	import com.google.common.collect.Iterables;
	import com.google.common.collect.LinkedHashMultimap;
	import com.google.common.collect.Lists;
	import com.google.common.collect.Multimap;
	import com.google.common.collect.SetMultimap;
	import com.google.devtools.build.lib.analysis.config.transitions.ConfigurationTransition;
	import com.google.devtools.build.lib.cmdline.Label;
	import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
	import com.google.devtools.build.lib.packages.ConfigurationFragmentPolicy.MissingFragmentPolicy;
	import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
	import com.google.devtools.build.lib.syntax.Type;
	import com.google.devtools.build.lib.syntax.Type.LabelClass;
	import com.google.devtools.build.lib.syntax.Type.LabelVisitor;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.LinkedHashMap;
	import java.util.LinkedHashSet;
	import java.util.List;
	import java.util.Map;
	import javax.annotation.Nullable;

	/**
	* The definition of an aspect (see {@link Aspect} for more information).
	*
	* <p>Contains enough information to build up the configured target graph except for the actual way
	* to build the Skyframe node (that is the territory of {@link com.google.devtools.build.lib.view
	* AspectFactory}). In particular:
	*
	* <ul>
	* <li>The condition that must be fulfilled for an aspect to be able to operate on a configured
	* target
	* <li>The (implicit or late-bound) attributes of the aspect that denote dependencies the aspect
	* itself needs (e.g. runtime libraries for a new language for protocol buffers)
	* <li>The aspects this aspect requires from its direct dependencies
	* </ul>
	*
	* <p>The way to build the Skyframe node is not here because this data needs to be accessible from
	* the {@code .packages} package and that one requires references to the {@code .view} package.
	*/
	@AutoCodec
	@Immutable
	public final class AspectDefinition {
	private final AspectClass aspectClass;
	private final AdvertisedProviderSet advertisedProviders;
	private final RequiredProviders requiredProviders;
	private final RequiredProviders requiredProvidersForAspects;
	private final ImmutableMap<String, Attribute> attributes;
	private final ImmutableSet<Label> requiredToolchains;

	/**
	* Which attributes aspect should propagate along:
	* <ul>
	* <li>A {@code null} value means propagate along all attributes</li>
	* <li>A (possibly empty) set means to propagate only along the attributes in a set</li>
	* </ul>
	*/
	@Nullable private final ImmutableSet<String> restrictToAttributes;
	@Nullable private final ConfigurationFragmentPolicy configurationFragmentPolicy;
	private final boolean applyToFiles;

	public AdvertisedProviderSet getAdvertisedProviders() {
	return advertisedProviders;
	}

	@AutoCodec.VisibleForSerialization
	AspectDefinition(
	AspectClass aspectClass,
	AdvertisedProviderSet advertisedProviders,
	RequiredProviders requiredProviders,
	RequiredProviders requiredProvidersForAspects,
	ImmutableMap<String, Attribute> attributes,
	ImmutableSet<Label> requiredToolchains,
	@Nullable ImmutableSet<String> restrictToAttributes,
	@Nullable ConfigurationFragmentPolicy configurationFragmentPolicy,
	boolean applyToFiles) {
	this.aspectClass = aspectClass;
	this.advertisedProviders = advertisedProviders;
	this.requiredProviders = requiredProviders;
	this.requiredProvidersForAspects = requiredProvidersForAspects;

	this.attributes = attributes;
	this.requiredToolchains = requiredToolchains;
	this.restrictToAttributes = restrictToAttributes;
	this.configurationFragmentPolicy = configurationFragmentPolicy;
	this.applyToFiles = applyToFiles;
	}

	public String getName() {
	return aspectClass.getName();
	}

	public AspectClass getAspectClass() {
	return aspectClass;
	}

	/**
	* Returns the attributes of the aspect in the form of a String -> {@link Attribute} map.
	*
	* <p>All attributes are either implicit or late-bound.
	*/
	public ImmutableMap<String, Attribute> getAttributes() {
	return attributes;
	}

	/** Returns the required toolchains declared by this aspect. */
	public ImmutableSet<Label> getRequiredToolchains() {
	return requiredToolchains;
	}

	/**
	* Returns {@link RequiredProviders} that a configured target must have so that
	* this aspect can be applied to it.
	*
	* <p>If a configured target does not satisfy required providers, the aspect is
	* silently not created for it.
	*/
	public RequiredProviders getRequiredProviders() {
	return requiredProviders;
	}

	/**
	* Aspects do not depend on other aspects applied to the same target <em>unless</em>
	* the other aspect satisfies the {@link RequiredProviders} this method returns
	*/
	public RequiredProviders getRequiredProvidersForAspects() {
	return requiredProvidersForAspects;
	}

	/** Returns the set of required aspects for a given attribute. */
	public boolean propagateAlong(String attributeName) {
	if (restrictToAttributes != null) {
	return restrictToAttributes.contains(attributeName);
	}
	return true;
	}

	/**
	* Returns the set of configuration fragments required by this Aspect.
	*/
	public ConfigurationFragmentPolicy getConfigurationFragmentPolicy() {
	return configurationFragmentPolicy;
	}

	/**
	* Returns whether this aspect applies to (output) files.
	*
	* Currently only supported for top-level aspects and targets, and
	* only for output files.
	*/
	public boolean applyToFiles() {
	return applyToFiles;
	}

	/**
	* Returns the attribute -> set of labels that are provided by aspects of attribute.
	*/
	public static ImmutableMultimap<Attribute, Label> visitAspectsIfRequired(
	Target from, Attribute attribute, Target to,
	DependencyFilter dependencyFilter) {
	// Aspect can be declared only for Rules.
	if (!(from instanceof Rule) \|\| !(to instanceof Rule)) {
	return ImmutableMultimap.of();
	}
	RuleClass ruleClass = ((Rule) to).getRuleClassObject();
	AdvertisedProviderSet providers = ruleClass.getAdvertisedProviders();
	return visitAspectsIfRequired((Rule) from, attribute,
	providers, dependencyFilter);
	}

	/**
	* Returns the attribute -> set of labels that are provided by aspects of attribute.
	*/
	public static ImmutableMultimap<Attribute, Label> visitAspectsIfRequired(
	Rule from, Attribute attribute,
	AdvertisedProviderSet advertisedProviders,
	DependencyFilter dependencyFilter) {
	SetMultimap<Attribute, Label> result = LinkedHashMultimap.create();
	for (Aspect candidateClass : attribute.getAspects(from)) {
	// Check if target satisfies condition for this aspect (has to provide all required
	// TransitiveInfoProviders)
	RequiredProviders requiredProviders =
	candidateClass.getDefinition().getRequiredProviders();
	if (requiredProviders.isSatisfiedBy(advertisedProviders)) {
	addAllAttributesOfAspect(from, result, candidateClass, dependencyFilter);
	}
	}
	return ImmutableMultimap.copyOf(result);
	}

	@Nullable
	private static Label maybeGetRepositoryRelativeLabel(Rule from, @Nullable Label label) {
	return label == null ? null : from.getLabel().resolveRepositoryRelative(label);
	}

	/**
	* Collects all attribute labels from the specified aspectDefinition.
	*/
	public static void addAllAttributesOfAspect(
	final Rule from,
	final Multimap<Attribute, Label> labelBuilder,
	Aspect aspect,
	DependencyFilter dependencyFilter) {
	LabelVisitor<Attribute> labelVisitor =
	(label, aspectAttribute) -> {
	Label repositoryRelative = maybeGetRepositoryRelativeLabel(from, label);
	if (repositoryRelative == null) {
	return;
	}
	labelBuilder.put(aspectAttribute, repositoryRelative);
	};
	ImmutableMap<String, Attribute> attributes = aspect.getDefinition().getAttributes();
	for (final Attribute aspectAttribute : attributes.values()) {
	if (!dependencyFilter.apply(aspect, aspectAttribute)) {
	continue;
	}
	Type<?> type = aspectAttribute.getType();
	if (type.getLabelClass() != LabelClass.DEPENDENCY) {
	continue;
	}
	type.visitLabels(labelVisitor, aspectAttribute.getDefaultValue(from), aspectAttribute);
	}
	}

	public static Builder builder(AspectClass aspectClass) {
	return new Builder(aspectClass);
	}

	/**
	* Builder class for {@link AspectDefinition}.
	*/
	public static final class Builder {
	private final AspectClass aspectClass;
	private final Map<String, Attribute> attributes = new LinkedHashMap<>();
	private final AdvertisedProviderSet.Builder advertisedProviders =
	AdvertisedProviderSet.builder();
	private RequiredProviders.Builder requiredProviders = RequiredProviders.acceptAnyBuilder();
	private RequiredProviders.Builder requiredAspectProviders =
	RequiredProviders.acceptNoneBuilder();
	@Nullable
	private LinkedHashSet<String> propagateAlongAttributes = new LinkedHashSet<>();
	private final ConfigurationFragmentPolicy.Builder configurationFragmentPolicy =
	new ConfigurationFragmentPolicy.Builder();
	private boolean applyToFiles = false;
	private final List<Label> requiredToolchains = new ArrayList<>();

	public Builder(AspectClass aspectClass) {
	this.aspectClass = aspectClass;
	}

	/**
	* Asserts that this aspect can only be evaluated for rules that supply all of the providers
	* from at least one set of required providers.
	*/
	public Builder requireProviderSets(Iterable<ImmutableSet<Class<?>>> providerSets) {
	for (ImmutableSet<Class<?>> providerSet : providerSets) {
	requiredProviders.addNativeSet(providerSet);
	}
	return this;
	}

	/**
	* Asserts that this aspect can only be evaluated for rules that supply all of the specified
	* providers.
	*/
	public Builder requireProviders(Class<?>... providers) {
	requiredProviders.addNativeSet(ImmutableSet.copyOf(providers));
	return this;
	}

	/**
	* Asserts that this aspect can only be evaluated for rules that supply all of the specified
	* Skylark providers.
	*/
	public Builder requireSkylarkProviders(SkylarkProviderIdentifier... skylarkProviders) {
	requiredProviders.addSkylarkSet(ImmutableSet.copyOf(skylarkProviders));
	return this;
	}

	public Builder requireAspectsWithProviders(
	Iterable<ImmutableSet<SkylarkProviderIdentifier>> providerSets) {
	for (ImmutableSet<SkylarkProviderIdentifier> providerSet : providerSets) {
	if (!providerSet.isEmpty()) {
	requiredAspectProviders.addSkylarkSet(providerSet);
	}
	}
	return this;
	}

	public Builder requireAspectsWithNativeProviders(
	Class<?>... providers) {
	requiredAspectProviders.addNativeSet(ImmutableSet.copyOf(providers));
	return this;
	}

	/**
	* State that the aspect being built provides given providers.
	*/
	public Builder advertiseProvider(Class<?>... providers) {
	for (Class<?> provider : providers) {
	advertisedProviders.addNative(provider);
	}
	return this;
	}

	/**
	* State that the aspect being built provides given providers.
	*/
	public Builder advertiseProvider(ImmutableList<SkylarkProviderIdentifier> providers) {
	for (SkylarkProviderIdentifier provider : providers) {
	advertisedProviders.addSkylark(provider);
	}
	return this;
	}



	/**
	* Declares that this aspect propagates along an {@code attribute} on the target
	* associated with this aspect.
	*
	* Specify multiple attributes by calling {@link #propagateAlongAttribute(String)}
	* repeatedly.
	*
	* Aspect can also declare to propagate along all attributes with
	* {@link #propagateAlongAttributes}.
	*/
	public final Builder propagateAlongAttribute(String attribute) {
	Preconditions.checkNotNull(attribute);
	Preconditions.checkState(this.propagateAlongAttributes != null,
	"Either propagate along all attributes, or along specific attributes, not both");

	this.propagateAlongAttributes.add(attribute);

	return this;
	}

	/**
	* Declares that this aspect propagates along all attributes on the target
	* associated with this aspect.
	*
	* Specify either this or {@link #propagateAlongAttribute(String)}, not both.
	*/
	public final Builder propagateAlongAllAttributes() {
	Preconditions.checkState(this.propagateAlongAttributes != null,
	"Aspects for all attributes must only be specified once");

	Preconditions.checkState(this.propagateAlongAttributes.isEmpty(),
	"Specify either aspects for all attributes, or for specific attributes, not both");
	this.propagateAlongAttributes = null;
	return this;
	}

	/**
	* Adds an attribute to the aspect.
	*
	* <p>Since aspects do not appear in BUILD files, the attribute must be either implicit
	* (not available in the BUILD file, starting with '$') or late-bound (determined after the
	* configuration is available, starting with ':')
	*/
	public <TYPE> Builder add(Attribute.Builder<TYPE> attr) {
	Attribute attribute = attr.build();
	return add(attribute);
	}

	/**
	* Adds an attribute to the aspect.
	*
	* <p>Since aspects do not appear in BUILD files, the attribute must be either implicit
	* (not available in the BUILD file, starting with '$') or late-bound (determined after the
	* configuration is available, starting with ':')
	*/
	public Builder add(Attribute attribute) {
	Preconditions.checkArgument(attribute.isImplicit() \|\| attribute.isLateBound()
	\|\| (attribute.getType() == Type.STRING && attribute.checkAllowedValues()),
	"Invalid attribute '%s' (%s)", attribute.getName(), attribute.getType());
	Preconditions.checkArgument(!attributes.containsKey(attribute.getName()),
	"An attribute with the name '%s' already exists.", attribute.getName());
	attributes.put(attribute.getName(), attribute);
	return this;
	}

	/**
	* Declares that the implementation of the associated aspect definition requires the given
	* fragments to be present in this rule's host and target configurations.
	*
	* <p>The value is inherited by subclasses.
	*/
	public Builder requiresConfigurationFragments(Class<?>... configurationFragments) {
	configurationFragmentPolicy
	.requiresConfigurationFragments(ImmutableSet.copyOf(configurationFragments));
	return this;
	}

	/**
	* Declares that the implementation of the associated aspect definition requires the given
	* fragments to be present in the given configuration that isn't the aspect's configuration but
	* is also readable by the aspect.
	*
	* <p>You probably don't want to use this, because aspects generally shouldn't read
	* configurations other than their own. If you want to declare host config fragments, see
	* {@link com.google.devtools.build.lib.analysis.config.ConfigAwareAspectBuilder}.
	*
	* <p>The value is inherited by subclasses.
	*/
	public Builder requiresConfigurationFragments(ConfigurationTransition transition,
	Class<?>... configurationFragments) {
	configurationFragmentPolicy.requiresConfigurationFragments(transition,
	ImmutableSet.copyOf(configurationFragments));
	return this;
	}

	/**
	* Declares the configuration fragments that are required by this rule for the target
	* configuration.
	*
	* <p>In contrast to {@link #requiresConfigurationFragments(Class...)}, this method takes the
	* Skylark module names of fragments instead of their classes.
	*/
	public Builder requiresConfigurationFragmentsBySkylarkModuleName(
	Collection<String> configurationFragmentNames) {
	configurationFragmentPolicy
	.requiresConfigurationFragmentsBySkylarkModuleName(configurationFragmentNames);
	return this;
	}

	/**
	* Declares that the implementation of the associated aspect definition requires the given
	* fragments to be present in the given configuration that isn't the aspect's configuration but
	* is also readable by the aspect.
	*
	* <p>In contrast to {@link #requiresConfigurationFragments(ConfigurationTransition, Class...)},
	* this method takes the Skylark module names of fragments instead of their classes.
	*
	* <p>You probably don't want to use this, because aspects generally shouldn't read
	* configurations other than their own. If you want to declare host config fragments, see
	* {@link com.google.devtools.build.lib.analysis.config.ConfigAwareAspectBuilder}.
	*/
	public Builder requiresConfigurationFragmentsBySkylarkModuleName(
	ConfigurationTransition transition, Collection<String> configurationFragmentNames) {
	configurationFragmentPolicy.requiresConfigurationFragmentsBySkylarkModuleName(transition,
	configurationFragmentNames);
	return this;
	}

	/**
	* Sets the policy for the case where the configuration is missing required fragments (see
	* {@link #requiresConfigurationFragments}).
	*/
	public Builder setMissingFragmentPolicy(MissingFragmentPolicy missingFragmentPolicy) {
	configurationFragmentPolicy.setMissingFragmentPolicy(missingFragmentPolicy);
	return this;
	}

	/**
	* Sets whether this aspect should apply to files.
	*
	* Default is <code>false</code>.
	* Currently only supported for top-level aspects and targets, and only for
	* output files.
	*/
	public Builder applyToFiles(boolean propagateOverGeneratedFiles) {
	this.applyToFiles = propagateOverGeneratedFiles;
	return this;
	}

	/** Adds the given toolchains as requirements for this aspect. */
	public Builder addRequiredToolchains(Label... toolchainLabels) {
	Iterables.addAll(this.requiredToolchains, Lists.newArrayList(toolchainLabels));
	return this;
	}

	/** Adds the given toolchains as requirements for this aspect. */
	public Builder addRequiredToolchains(List<Label> requiredToolchains) {
	this.requiredToolchains.addAll(requiredToolchains);
	return this;
	}
	/**
	* Builds the aspect definition.
	*
	* <p>The builder object is reusable afterwards.
	*/
	public AspectDefinition build() {
	return new AspectDefinition(
	aspectClass,
	advertisedProviders.build(),
	requiredProviders.build(),
	requiredAspectProviders.build(),
	ImmutableMap.copyOf(attributes),
	ImmutableSet.copyOf(requiredToolchains),
	propagateAlongAttributes == null ? null : ImmutableSet.copyOf(propagateAlongAttributes),
	configurationFragmentPolicy.build(),
	applyToFiles);
	}
	}
	}