// 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.analysis; import com.google.common.collect.UnmodifiableIterator; import com.google.devtools.build.lib.analysis.config.BuildConfiguration; import com.google.devtools.build.lib.cmdline.Label; import com.google.devtools.build.lib.syntax.SkylarkModule; import javax.annotation.Nullable; /** * Objects that implement this interface bundle multiple {@link TransitiveInfoProvider} interfaces. * *
This interface (together with {@link TransitiveInfoProvider} is the cornerstone of the data * model of the analysis phase. * *
The computation a configured target does is allowed to depend on the following things: *
And these are the only inputs. Notably, a configured target is not supposed to access * other configured targets, the transitive info collections of configured targets it does not * directly depend on, the actions created by anyone else or the contents of any input file. We * strive to make it impossible for configured targets to do these things. * *
A configured target is expected to produce the following data during its analysis: *
The information that can be passed on to dependent targets by way of * {@link TransitiveInfoProvider} is subject to constraints (which are detailed in the * documentation of that class). * *
Configured targets are currently allowed to create artifacts at any exec path. It would be * better if they could be constrained to a subtree based on the label of the configured target, * but this is currently not feasible because multiple rules violate this constraint and the * output format is part of its interface. * *
In principle, multiple configured targets should not create actions with conflicting * outputs. There are still a few exceptions to this rule that are slated to be eventually * removed, we have provisions to handle this case (Action instances that share at least one * output file are required to be exactly the same), but this does put some pressure on the design * and we are eventually planning to eliminate this option. * *
These restrictions together make it possible to: *
Implementations of build rules should not hold on to references to the
* {@link TransitiveInfoCollection}s representing their direct prerequisites in order to reduce
* their memory footprint (otherwise, the referenced object could refer one of its direct
* dependencies in turn, thereby making the size of the objects reachable from a single instance
* unbounded).
*
* @see TransitiveInfoProvider
*/
@SkylarkModule(name = "Target", doc =
"A BUILD target. It is essentially a struct
with the following fields:"
+ "
Label Target.label
set Target.files
struct
fields. "
+ "These extra providers are defined in the struct
returned by the rule "
+ "implementation function.P getProvider(Class
provider); /** * Returns the label associated with this prerequisite. */ Label getLabel(); /** *
Returns the {@link BuildConfiguration} for which this transitive info collection is defined. * Configuration is defined for all configured targets with exception of {@link * InputFileConfiguredTarget} and {@link PackageGroupConfiguredTarget} for which it is always * null.
*/ @Nullable BuildConfiguration getConfiguration(); /** * Returns the transitive information requested or null, if the information is not found. * The transitive information has to have been added using the Skylark framework. */ @Nullable Object get(String providerKey); /** * Returns an unmodifiable iterator over the transitive info providers in the collections. */ @Override UnmodifiableIterator