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// Copyright 2014 Google Inc. 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.query2.engine;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.Argument;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.ArgumentType;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryFunction;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
/**
* An "rdeps" query expression, which computes the reverse dependencies of the argument within the
* transitive closure of the universe. An optional integer-literal third argument may be
* specified; its value bounds the search from the arguments.
*
* <pre>expr ::= RDEPS '(' expr ',' expr ')'</pre>
* <pre> | RDEPS '(' expr ',' expr ',' WORD ')'</pre>
*/
final class RdepsFunction implements QueryFunction {
RdepsFunction() {
}
@Override
public String getName() {
return "rdeps";
}
@Override
public int getMandatoryArguments() {
return 2; // last argument is optional
}
@Override
public List<ArgumentType> getArgumentTypes() {
return ImmutableList.of(
ArgumentType.EXPRESSION, ArgumentType.EXPRESSION, ArgumentType.INTEGER);
}
/**
* Compute the transitive closure of the universe, then breadth-first search from the argument
* towards the universe while staying within the transitive closure.
*/
@Override
public <T> Set<T> eval(QueryEnvironment<T> env, QueryExpression expression, List<Argument> args)
throws QueryException {
Set<T> universeValue = args.get(0).getExpression().eval(env);
Set<T> argumentValue = args.get(1).getExpression().eval(env);
int depthBound = args.size() > 2 ? args.get(2).getInteger() : Integer.MAX_VALUE;
env.buildTransitiveClosure(expression, universeValue, Integer.MAX_VALUE);
Set<T> visited = new LinkedHashSet<>();
Set<T> reachableFromUniverse = env.getTransitiveClosure(universeValue);
Collection<T> current = argumentValue;
// We need to iterate depthBound + 1 times.
for (int i = 0; i <= depthBound; i++) {
List<T> next = new ArrayList<>();
// Restrict to nodes in our universe.
Iterable<T> currentInUniverse = Iterables.filter(current,
Predicates.in(reachableFromUniverse));
// Filter already visited nodes: if we see a node in a later round, then we don't need to
// visit it again, because the depth at which we see it at must be greater than or equal to
// the last visit.
next.addAll(env.getReverseDeps(Iterables.filter(currentInUniverse,
Predicates.not(Predicates.in(visited)))));
Iterables.addAll(visited, currentInUniverse);
if (next.isEmpty()) {
// Exit when there are no more nodes to visit.
break;
}
current = next;
}
return visited;
}
}
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