https://www.graalvm.org/ 
/*
 * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * The Universal Permissive License (UPL), Version 1.0
 *
 * Subject to the condition set forth below, permission is hereby granted to any
 * person obtaining a copy of this software, associated documentation and/or
 * data (collectively the "Software"), free of charge and under any and all
 * copyright rights in the Software, and any and all patent rights owned or
 * freely licensable by each licensor hereunder covering either (i) the
 * unmodified Software as contributed to or provided by such licensor, or (ii)
 * the Larger Works (as defined below), to deal in both
 *
 * (a) the Software, and
 *
 * (b) any piece of software and/or hardware listed in the lrgrwrks.txt file if
 * one is included with the Software each a "Larger Work" to which the Software
 * is contributed by such licensors),
 *
 * without restriction, including without limitation the rights to copy, create
 * derivative works of, display, perform, and distribute the Software and make,
 * use, sell, offer for sale, import, export, have made, and have sold the
 * Software and the Larger Work(s), and to sublicense the foregoing rights on
 * either these or other terms.
 *
 * This license is subject to the following condition:
 *
 * The above copyright notice and either this complete permission notice or at a
 * minimum a reference to the UPL must be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.oracle.truffle.api.instrumentation;

import static java.lang.annotation.ElementType.TYPE;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Objects;

import com.oracle.truffle.api.impl.Accessor.EngineSupport;
import com.oracle.truffle.api.nodes.LanguageInfo;
import java.util.Set;


Base class for tags used in the Truffle instrumentation framework.

See Also:
Since:0.33
/**
 * Base class for tags used in the Truffle instrumentation framework.
 *
 * @see StandardTags For the standard set of tags
 * @see #findProvidedTag(LanguageInfo, String) to find a provided tag of a language
 * @since 0.33
 */
public abstract class Tag {

    
No instances of tags allowed. Tags are marker classes.

Since:0.33
/**
     * No instances of tags allowed. Tags are marker classes.
     *
     * @since 0.33
     */
    protected Tag() {
        throw new AssertionError("No tag instances allowed.");
    }

    
Finds a provided tag by the language using its identifier. If the language implementation class is not yet loaded then this method will force the loading. Therefore it is not recommended to iterate over the entire list of languages and request all provided tags. It is guaranteed that there is only one provided tag class per tag identifier and language. For different languages the same tag id might refer to different tag classes. 
Since:0.33
/**
     * Finds a provided tag by the language using its {@link Tag.Identifier identifier}. If the
     * language implementation class is not yet loaded then this method will force the loading.
     * Therefore it is not recommended to iterate over the entire list of languages and request all
     * provided tags. It is guaranteed that there is only one provided tag class per tag identifier
     * and language. For different languages the same tag id might refer to different tag classes.
     *
     * @since 0.33
     */
    @SuppressWarnings("unchecked")
    public static Class<? extends Tag> findProvidedTag(LanguageInfo language, String tagId) {
        Objects.requireNonNull(language);
        Objects.requireNonNull(tagId);
        EngineSupport engine = InstrumentAccessor.engineAccess();
        if (engine == null) {
            return null;
        }
        for (Class<? extends Tag> tag : (Set<? extends Class<? extends Tag>>) engine.getProvidedTags(language)) {
            String alias = getIdentifier(tag);
            if (alias != null && alias.equals(tagId)) {
                return tag;
            }
        }
        return null;
    }

    
Returns the alias of a particular tag or null if no alias was specified for this
tag.

Params:
  • tag – the tag to return the alias for.
Returns:the alias string
Since:0.33
/**
     * Returns the alias of a particular tag or <code>null</code> if no alias was specified for this
     * tag.
     *
     * @param tag the tag to return the alias for.
     * @return the alias string
     * @since 0.33
     */
    public static String getIdentifier(Class<? extends Tag> tag) {
        Objects.requireNonNull(tag);
        Tag.Identifier alias = tag.getAnnotation(Tag.Identifier.class);
        if (alias != null) {
            return alias.value();
        }
        return null;
    }

    
Annotation applied to Tag subclasses to specify the tag identifier. The tag identifier can be used to find and load tag classes used by tools. 
Since:0.33
/**
     * Annotation applied to {@link Tag} subclasses to specify the tag identifier. The tag
     * identifier can be used to {@link Tag#findProvidedTag(LanguageInfo, String) find} and load tag
     * classes used by tools.
     *
     * @since 0.33
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(value = TYPE)
    public @interface Identifier {

        
Returns the identifier value as string.

Since:0.33
/**
         * Returns the identifier value as string.
         *
         * @since 0.33
         */
        String value();

    }

}