folly/folly/logging/Logger.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

#pragma once

#include <folly/logging/LogCategory.h>
#include <folly/logging/LogLevel.h>
#include <folly/logging/LogStream.h>
#include <folly/logging/LogStreamProcessor.h>

/**
 * Log a message to the specified logger.
 *
 * This macro avoids evaluating the log arguments unless the log level check
 * succeeds.
 *
 * Beware that the logger argument is evaluated twice, so this argument should
 * be an expression with no side-effects.
 */
#define FB_LOG(logger, level, ...) …

/**
 * Log a message to the specified logger, using a fmt::format() string.
 *
 * The arguments will be processed using fmt::format().  The format syntax
 * is similar to Python format strings.
 *
 * This macro avoids evaluating the log arguments unless the log level check
 * succeeds.
 *
 * Beware that the logger argument is evaluated twice, so this argument should
 * be an expression with no side-effects.
 */
#define FB_LOGF(logger, level, fmt, arg1, ...) …

/**
 * FB_LOG_RAW() can be used by callers that want to pass in the log level as a
 * variable, and/or who want to explicitly specify the filename and line
 * number.
 *
 * This is useful for callers implementing their own log wrapper functions
 * that want to pass in their caller's filename and line number rather than
 * their own.
 *
 * The log level parameter must be an explicitly qualified LogLevel value, or a
 * LogLevel variable.  (This differs from FB_LOG() and FB_LOGF() which accept
 * an unqualified LogLevel name.)
 */
#define FB_LOG_RAW(logger, level, filename, linenumber, functionName, ...) …

/**
 * FB_LOGF_RAW() is similar to FB_LOG_RAW(), but formats the log arguments
 * using fmt::format().
 */
#define FB_LOGF_RAW(                                                   \
    logger, level, filename, linenumber, functionName, fmt, arg1, ...) …

/**
 * Helper macro for implementing FB_LOG() and FB_LOGF().
 *
 * This macro generally should not be used directly by end users.
 */
#define FB_LOG_IMPL(logger, level, type, ...) …

/**
 * Helper macro for implementing FB_LOG_RAW() and FB_LOGF_RAW().
 *
 * This macro generally should not be used directly by end users.
 *
 * This is very similar to FB_LOG_IMPL(), but since the level may be a variable
 * instead of a compile-time constant, we cannot detect at compile time if this
 * is a fatal log message or not.
 */
#define FB_LOG_RAW_IMPL(                                    \
    logger, level, filename, line, functionName, type, ...) …

namespace folly {

class LoggerDB;
class LogMessage;

/**
 * Logger is the class you will use to specify the log category when logging
 * messages with FB_LOG().
 *
 * Logger is really just a small wrapper class that contains a pointer to the
 * appropriate LogCategory object.  It primarily exists as syntactic sugar to
 * allow for easily looking up LogCategory objects.
 */
class Logger { … };
} // namespace folly