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There is a newer version: 3.0.23
/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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 groovy.util.logging;

import groovy.lang.GroovyClassLoader;
import groovy.transform.Undefined;
import org.codehaus.groovy.ast.ClassNode;
import org.codehaus.groovy.ast.FieldNode;
import org.codehaus.groovy.ast.expr.ArgumentListExpression;
import org.codehaus.groovy.ast.expr.ClassExpression;
import org.codehaus.groovy.ast.expr.ConstantExpression;
import org.codehaus.groovy.ast.expr.Expression;
import org.codehaus.groovy.ast.expr.MethodCallExpression;
import org.codehaus.groovy.transform.GroovyASTTransformationClass;
import org.codehaus.groovy.transform.LogASTTransformation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Locale;

import static org.codehaus.groovy.ast.tools.GeneralUtils.nullX;
import static org.codehaus.groovy.ast.tools.GeneralUtils.ternaryX;

/**
 * This local transform adds a logging ability to your program using
 * LogBack logging. Every method call on a unbound variable named log
 * will be mapped to a call to the logger. For this a log field will be
 * inserted in the class. If the field already exists the usage of this transform
 * will cause a compilation error. The method name will be used to determine
 * what to call on the logger.
 *  * log.name(exp)
 * is mapped to
 *  * if (log.isNameLoggable() {
 *    log.name(exp)
 * }
 * Here name is a place holder for info, debug, warning, error, etc.
 * If the expression exp is a constant or only a variable access the method call will
 * not be transformed. But this will still cause a call on the injected logger.
 *
 * @since 1.8.0
 */
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.LogASTTransformation")
public @interface Slf4j {
    String value() default "log";
    String category() default LogASTTransformation.DEFAULT_CATEGORY_NAME;

    /**
     * If specified, must match the "id" attribute in a VisibilityOptions annotation to enable a custom visibility.
     * @since 3.0.0
     */
    String visibilityId() default Undefined.STRING;

    Class loggingStrategy() default Slf4jLoggingStrategy.class;

    class Slf4jLoggingStrategy extends LogASTTransformation.AbstractLoggingStrategyV2 {
        private static final String LOGGER_NAME = "org.slf4j.Logger";
        private static final String FACTORY_NAME = "org.slf4j.LoggerFactory";

        protected Slf4jLoggingStrategy(final GroovyClassLoader loader) {
            super(loader);
        }

        @Override
        public FieldNode addLoggerFieldToClass(ClassNode classNode, String logFieldName, String categoryName, int fieldModifiers) {
            return classNode.addField(logFieldName,
                    fieldModifiers,
                    classNode(LOGGER_NAME),
                    new MethodCallExpression(
                            new ClassExpression(classNode(FACTORY_NAME)),
                            "getLogger",
                            new ConstantExpression(getCategoryName(classNode, categoryName))));
        }

        @Override
        public boolean isLoggingMethod(String methodName) {
            return methodName.matches("error|warn|info|debug|trace");
        }

        @Override
        public Expression wrapLoggingMethodCall(Expression logVariable, String methodName, Expression originalExpression) {
            MethodCallExpression condition = new MethodCallExpression(
                    logVariable,
                    "is" + methodName.substring(0, 1).toUpperCase(Locale.ENGLISH) + methodName.substring(1) + "Enabled",
                    ArgumentListExpression.EMPTY_ARGUMENTS);
            condition.setImplicitThis(false);

            return ternaryX(condition, originalExpression, nullX());
        }
    }
}