src/main/java/com/google/devtools/build/lib/query2/engine/SetExpression.java

// 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.query2.engine;

import com.google.common.base.Joiner;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryTaskFuture;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * A set(word, ..., word) expression, which computes the union of zero or more
 * target patterns separated by whitespace.  This is intended to support the
 * use-case in which a set of labels written to a file by a previous query
 * expression can be modified externally, then used as input to another query,
 * like so:
 *
 * <pre>
 * % blaze query 'somepath(foo, bar)' | grep ... | sed ... | awk ... >file
 * % blaze query "kind(qux_library, set($(<file)))"
 * </pre>
 *
 * <p>The grammar currently restricts the operands of set() to being zero or
 * more words (target patterns), with no intervening punctuation.  In principle
 * this could be extended to arbitrary expressions without grammatical
 * ambiguity, but this seems excessively general for now.
 *
 * <pre>expr ::= SET '(' WORD * ')'</pre>
 */
public class SetExpression extends QueryExpression {

  private final List<TargetLiteral> words;

  public SetExpression(List<TargetLiteral> words) {
    this.words = words;
  }

  @Override
  public <T> QueryTaskFuture<Void> eval(
      QueryEnvironment<T> env, QueryExpressionContext<T> context, Callback<T> callback) {
    ArrayList<QueryTaskFuture<Void>> queryTasks = new ArrayList<>(words.size());
    for (TargetLiteral expr : words) {
      queryTasks.add(env.eval(expr, context, callback));
    }
    return env.whenAllSucceed(queryTasks);
  }

  @Override
  public void collectTargetPatterns(Collection<String> literals) {
    for (TargetLiteral expr : words) {
      expr.collectTargetPatterns(literals);
    }
  }

  @Override
  public <T, C> T accept(QueryExpressionVisitor<T, C> visitor, C context) {
    return visitor.visit(this, context);
  }

  /** Gets the list of {@link TargetLiteral}s contained in the expression. */
  public List<TargetLiteral> getWords() {
    return words;
  }

  @Override
  public String toString() {
    return "set(" + Joiner.on(' ').join(words) + ")";
  }
}