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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.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.common.collect.Sets.SetView;
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.HashSet;
import java.util.List;
import java.util.Set;
/**
* A somepath(x, y) query expression, which computes the set of nodes
* on some arbitrary path from a target in set x to a target in set y.
*
* <pre>expr ::= SOMEPATH '(' expr ',' expr ')'</pre>
*/
class SomePathFunction implements QueryFunction {
SomePathFunction() {
}
@Override
public String getName() {
return "somepath";
}
@Override
public int getMandatoryArguments() {
return 2;
}
@Override
public List<ArgumentType> getArgumentTypes() {
return ImmutableList.of(ArgumentType.EXPRESSION, ArgumentType.EXPRESSION);
}
@Override
public <T> Set<T> eval(QueryEnvironment<T> env, QueryExpression expression, List<Argument> args)
throws QueryException, InterruptedException {
Set<T> fromValue = args.get(0).getExpression().eval(env);
Set<T> toValue = args.get(1).getExpression().eval(env);
// Implementation strategy: for each x in "from", compute its forward
// transitive closure. If it intersects "to", then do a path search from x
// to an arbitrary node in the intersection, and return the path. This
// avoids computing the full transitive closure of "from" in some cases.
env.buildTransitiveClosure(expression, fromValue, Integer.MAX_VALUE);
// This set contains all nodes whose TC does not intersect "toValue".
Set<T> done = new HashSet<>();
for (T x : fromValue) {
if (done.contains(x)) {
continue;
}
Set<T> xtc = env.getTransitiveClosure(ImmutableSet.of(x));
SetView<T> result;
if (xtc.size() > toValue.size()) {
result = Sets.intersection(toValue, xtc);
} else {
result = Sets.intersection(xtc, toValue);
}
if (!result.isEmpty()) {
return env.getNodesOnPath(x, result.iterator().next());
}
done.addAll(xtc);
}
return ImmutableSet.of();
}
}
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