com.google.devtools.build.lib.syntax.SelectorList.java Source code

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Here is the source code for com.google.devtools.build.lib.syntax.SelectorList.java

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// Copyright 2015 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.syntax;

import com.google.common.collect.ImmutableList;
import com.google.devtools.build.lib.events.Location;
import com.google.devtools.build.lib.skylarkinterface.SkylarkModule;
import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;

import java.util.ArrayList;
import java.util.List;

/**
 * An attribute value consisting of a concatenation of native types and selects, e.g:
 *
 * <pre>
 *   rule(
 *       name = 'myrule',
 *       deps =
 *           [':defaultdep']
 *           + select({
 *               'a': [':adep'],
 *               'b': [':bdep'],})
 *           + select({
 *               'c': [':cdep'],
 *               'd': [':ddep'],})
 *   )
 * </pre>
 */
@SkylarkModule(name = "select", doc = "A selector between configuration-dependent entities.", documented = false)
public final class SelectorList implements SkylarkValue {
    // TODO(build-team): Selectors are currently split between .packages and .syntax . They should
    // really all be in .packages, but then we'd need to figure out a way how to extend binary
    // operators, which is a non-trivial problem.
    private final Class<?> type;
    private final List<Object> elements;

    private SelectorList(Class<?> type, List<Object> elements) {
        this.type = type;
        this.elements = elements;
    }

    /**
     * Returns an ordered list of the elements in this expression. Each element may be a
     * native type or a select.
     */
    public List<Object> getElements() {
        return elements;
    }

    /**
     * Returns the native type contained by this expression.
     */
    public Class<?> getType() {
        return type;
    }

    /**
     * Creates a "wrapper" list that consists of a single select.
     */
    public static SelectorList of(SelectorValue selector) {
        return new SelectorList(selector.getType(), ImmutableList.<Object>of(selector));
    }

    /**
     * Creates a list that concatenates two values, where each value may be either a native
     * type or a select over that type.
     *
     * @throws EvalException if the values don't have the same underlying type
     */
    public static SelectorList concat(Location location, Object value1, Object value2) throws EvalException {
        ImmutableList.Builder<Object> builder = ImmutableList.builder();
        Class<?> type1 = addValue(value1, builder);
        Class<?> type2 = addValue(value2, builder);
        if (!canConcatenate(type1, type2)) {
            throw new EvalException(location, String.format("'+' operator applied to incompatible types (%s, %s)",
                    EvalUtils.getDataTypeName(value1, true), EvalUtils.getDataTypeName(value2, true)));
        }
        return new SelectorList(type1, builder.build());
    }

    // TODO(bazel-team): match on the List interface, not the actual implementation. For now,
    // we verify this is the right class through test coverage.
    private static final Class<?> NATIVE_LIST_TYPE = ArrayList.class;

    private static Class<?> addValue(Object value, ImmutableList.Builder<Object> builder) {
        if (value instanceof SelectorList) {
            SelectorList selectorList = (SelectorList) value;
            builder.addAll(selectorList.getElements());
            return selectorList.getType();
        } else if (value instanceof SelectorValue) {
            builder.add(value);
            return ((SelectorValue) value).getType();
        } else {
            builder.add(value);
            return value.getClass();
        }
    }

    private static boolean isListType(Class<?> type) {
        return type == NATIVE_LIST_TYPE || type.getSuperclass() == SkylarkList.class || type == GlobList.class;
    }

    private static boolean canConcatenate(Class<?> type1, Class<?> type2) {
        if (type1 == type2) {
            return true;
        } else if (isListType(type1) && isListType(type2)) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public String toString() {
        return Printer.repr(this);
    }

    @Override
    public void write(Appendable buffer, char quotationMark) {
        Printer.printList(buffer, elements, "", " + ", "", null, quotationMark);
    }

    @Override
    public boolean isImmutable() {
        return false;
    }
}