// 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.skyframe;
import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.util.Preconditions;
import com.google.devtools.build.skyframe.LegacySkyKey;
import com.google.devtools.build.skyframe.SkyFunctionName;
import com.google.devtools.build.skyframe.SkyKey;
/**
* A value for ensuring that an error for a cycle/chain is reported exactly once. This is achieved
* by forcing the same value key for two logically equivalent errors and letting Skyframe do its
* magic.
*/
class ChainUniquenessUtils {
private ChainUniquenessUtils() {}
/**
* Create a SkyKey for {@code functionName} with a canonicalized representation of the cycle
* specified by {@code chain} as the argument. {@code chain} must be non-empty.
*/
static SkyKey key(SkyFunctionName functionName, ImmutableList<? extends Object> chain) {
Preconditions.checkState(!chain.isEmpty());
return LegacySkyKey.create(functionName, canonicalize(chain));
}
private static ImmutableList<Object> canonicalize(ImmutableList<? extends Object> cycle) {
int minPos = 0;
String minString = cycle.get(0).toString();
for (int i = 1; i < cycle.size(); i++) {
// TOOD(bazel-team): Is the toString representation stable enough?
String candidateString = cycle.get(i).toString();
if (candidateString.compareTo(minString) < 0) {
minPos = i;
minString = candidateString;
}
}
ImmutableList.Builder<Object> builder = ImmutableList.builder();
for (int i = 0; i < cycle.size(); i++) {
int pos = (minPos + i) % cycle.size();
builder.add(cycle.get(pos));
}
return builder.build();
}
}