base/logging.h - chromium/src - Git at Google

 // Copyright 2012 The Chromium Authors
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #ifndef BASE_LOGGING_H_
 #define BASE_LOGGING_H_

 #include <stddef.h>

 #include <cassert>
 #include <cstdint>
 #include <sstream>
 #include <string>
 #include <string_view>

 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/dcheck_is_on.h"
 #include "base/functional/callback_forward.h"
 #include "base/logging_buildflags.h"
 #include "base/scoped_clear_last_error.h"
 #include "base/strings/string_piece_forward.h"
 #include "base/strings/utf_ostream_operators.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"

 #if BUILDFLAG(IS_CHROMEOS)
 #include <cstdio>
 #endif

 //
 // Optional message capabilities
 // -----------------------------
 // Assertion failed messages and fatal errors are displayed in a dialog box
 // before the application exits. However, running this UI creates a message
 // loop, which causes application messages to be processed and potentially
 // dispatched to existing application windows. Since the application is in a
 // bad state when this assertion dialog is displayed, these messages may not
 // get processed and hang the dialog, or the application might go crazy.
 //
 // Therefore, it can be beneficial to display the error dialog in a separate
 // process from the main application. When the logging system needs to display
 // a fatal error dialog box, it will look for a program called
 // "DebugMessage.exe" in the same directory as the application executable. It
 // will run this application with the message as the command line, and will
 // not include the name of the application as is traditional for easier
 // parsing.
 //
 // The code for DebugMessage.exe is only one line. In WinMain, do:
 //   MessageBox(NULL, GetCommandLineW(), L"Fatal Error", 0);
 //
 // If DebugMessage.exe is not found, the logging code will use a normal
 // MessageBox, potentially causing the problems discussed above.

 // Instructions
 // ------------
 //
 // Make a bunch of macros for logging.  The way to log things is to stream
 // things to LOG(<a particular severity level>).  E.g.,
 //
 //   LOG(INFO) << "Found " << num_cookies << " cookies";
 //
 // You can also do conditional logging:
 //
 //   LOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
 //
 // The CHECK(condition) macro is active in both debug and release builds and
 // effectively performs a LOG(FATAL) which terminates the process and
 // generates a crashdump unless a debugger is attached.
 //
 // There are also "debug mode" logging macros like the ones above:
 //
 //   DLOG(INFO) << "Found cookies";
 //
 //   DLOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
 //
 // All "debug mode" logging is compiled away to nothing for non-debug mode
 // compiles.  LOG_IF and development flags also work well together
 // because the code can be compiled away sometimes.
 //
 // We also have
 //
 //   LOG_ASSERT(assertion);
 //   DLOG_ASSERT(assertion);
 //
 // which is syntactic sugar for {,D}LOG_IF(FATAL, assert fails) << assertion;
 //
 // There are "verbose level" logging macros.  They look like
 //
 //   VLOG(1) << "I'm printed when you run the program with --v=1 or more";
 //   VLOG(2) << "I'm printed when you run the program with --v=2 or more";
 //
 // These always log at the INFO log level (when they log at all).
 //
 // There is a build flag USE_RUNTIME_VLOG that controls whether verbose
 // logging is processed at runtime or at build time.
 //
 // When USE_RUNTIME_VLOG is not set, the verbose logging is processed at
 // build time. VLOG(n) is only included and compiled when `n` is less than or
 // equal to the verbose level defined by ENABLED_VLOG_LEVEL macro. Command line
 // switch --v and --vmodule are ignored in this mode.
 //
 // When USE_RUNTIME_VLOG is set, the verbose logging is controlled at
 // runtime and can be turned on module-by-module.  For instance,
 //    --vmodule=profile=2,icon_loader=1,browser_*=3,*/chromeos/*=4 --v=0
 // will cause:
 //   a. VLOG(2) and lower messages to be printed from profile.{h,cc}
 //   b. VLOG(1) and lower messages to be printed from icon_loader.{h,cc}
 //   c. VLOG(3) and lower messages to be printed from files prefixed with
 //      "browser"
 //   d. VLOG(4) and lower messages to be printed from files under a
 //     "chromeos" directory.
 //   e. VLOG(0) and lower messages to be printed from elsewhere
 //
 // The wildcarding functionality shown by (c) supports both '*' (match
 // 0 or more characters) and '?' (match any single character)
 // wildcards.  Any pattern containing a forward or backward slash will
 // be tested against the whole pathname and not just the module.
 // E.g., "*/foo/bar/*=2" would change the logging level for all code
 // in source files under a "foo/bar" directory.
 //
 // Note that for a Chromium binary built in release mode (is_debug = false) you
 // must pass "--enable-logging=stderr" in order to see the output of VLOG
 // statements.
 //
 // There's also VLOG_IS_ON(n) "verbose level" condition macro. To be used as
 //
 //   if (VLOG_IS_ON(2)) {
 //     // do some logging preparation and logging
 //     // that can't be accomplished with just VLOG(2) << ...;
 //   }
 //
 // There is also a VLOG_IF "verbose level" condition macro for sample
 // cases, when some extra computation and preparation for logs is not
 // needed.
 //
 //   VLOG_IF(1, (size > 1024))
 //      << "I'm printed when size is more than 1024 and when you run the "
 //         "program with --v=1 or more";
 //
 // We also override the standard 'assert' to use 'DLOG_ASSERT'.
 //
 // Lastly, there is:
 //
 //   PLOG(ERROR) << "Couldn't do foo";
 //   DPLOG(ERROR) << "Couldn't do foo";
 //   PLOG_IF(ERROR, cond) << "Couldn't do foo";
 //   DPLOG_IF(ERROR, cond) << "Couldn't do foo";
 //   PCHECK(condition) << "Couldn't do foo";
 //   DPCHECK(condition) << "Couldn't do foo";
 //
 // which append the last system error to the message in string form (taken from
 // GetLastError() on Windows and errno on POSIX).
 //
 // The supported severity levels for macros that allow you to specify one
 // are (in increasing order of severity) INFO, WARNING, ERROR, and FATAL.
 //
 // Very important: logging a message at the FATAL severity level causes
 // the program to terminate (after the message is logged).
 //
 // There is the special severity of DFATAL, which logs FATAL in DCHECK-enabled
 // builds, ERROR in normal mode.
 //
 // Output is formatted as per the following example, except on Chrome OS.
 // [3816:3877:0812/234555.406952:VERBOSE1:drm_device_handle.cc(90)] Succeeded
 // authenticating /dev/dri/card0 in 0 ms with 1 attempt(s)
 //
 // The colon separated fields inside the brackets are as follows:
 // 0. An optional Logfile prefix (not included in this example)
 // 1. Process ID
 // 2. Thread ID
 // 3. The date/time of the log message, in MMDD/HHMMSS.Milliseconds format
 // 4. The log level
 // 5. The filename and line number where the log was instantiated
 //
 // Output for Chrome OS can be switched to syslog-like format. See
 // InitWithSyslogPrefix() in logging_chromeos.cc for details.
 //
 // Note that the visibility can be changed by setting preferences in
 // SetLogItems()
 //
 // Additional logging-related information can be found here:
 // https://chromium.googlesource.com/chromium/src/+/main/docs/linux/debugging.md#Logging

 namespace logging {

 // TODO(avi): do we want to do a unification of character types here?
 #if BUILDFLAG(IS_WIN)
 typedef wchar_t PathChar;
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 typedef char PathChar;
 #endif

 // A bitmask of potential logging destinations.
 using LoggingDestination = uint32_t;
 // Specifies where logs will be written. Multiple destinations can be specified
 // with bitwise OR.
 // Unless destination is LOG_NONE, all logs with severity ERROR and above will
 // be written to stderr in addition to the specified destination.
 enum : uint32_t {
   LOG_NONE = 0,
   LOG_TO_FILE = 1 << 0,
   LOG_TO_SYSTEM_DEBUG_LOG = 1 << 1,
   LOG_TO_STDERR = 1 << 2,

   LOG_TO_ALL = LOG_TO_FILE | LOG_TO_SYSTEM_DEBUG_LOG | LOG_TO_STDERR,

 // On Windows, use a file next to the exe.
 // On POSIX platforms, where it may not even be possible to locate the
 // executable on disk, use stderr.
 // On Fuchsia, use the Fuchsia logging service.
 #if BUILDFLAG(IS_FUCHSIA) || BUILDFLAG(IS_NACL)
   LOG_DEFAULT = LOG_TO_SYSTEM_DEBUG_LOG,
 #elif BUILDFLAG(IS_WIN)
   LOG_DEFAULT = LOG_TO_FILE,
 #elif BUILDFLAG(IS_POSIX)
   LOG_DEFAULT = LOG_TO_SYSTEM_DEBUG_LOG | LOG_TO_STDERR,
 #endif
 };

 // Indicates that the log file should be locked when being written to.
 // Unless there is only one single-threaded process that is logging to
 // the log file, the file should be locked during writes to make each
 // log output atomic. Other writers will block.
 //
 // All processes writing to the log file must have their locking set for it to
 // work properly. Defaults to LOCK_LOG_FILE.
 enum LogLockingState { LOCK_LOG_FILE, DONT_LOCK_LOG_FILE };

 // On startup, should we delete or append to an existing log file (if any)?
 // Defaults to APPEND_TO_OLD_LOG_FILE.
 enum OldFileDeletionState { DELETE_OLD_LOG_FILE, APPEND_TO_OLD_LOG_FILE };

 #if BUILDFLAG(IS_CHROMEOS)
 // Defines the log message prefix format to use.
 // LOG_FORMAT_SYSLOG indicates syslog-like message prefixes.
 // LOG_FORMAT_CHROME indicates the normal Chrome format.
 enum class BASE_EXPORT LogFormat { LOG_FORMAT_CHROME, LOG_FORMAT_SYSLOG };
 #endif

 struct BASE_EXPORT LoggingSettings {
   // Equivalent to logging destination enum, but allows for multiple
   // destinations.
   uint32_t logging_dest = LOG_DEFAULT;

   // The four settings below have an effect only when LOG_TO_FILE is
   // set in |logging_dest|.
   const PathChar* log_file_path = nullptr;
   LogLockingState lock_log = LOCK_LOG_FILE;
   OldFileDeletionState delete_old = APPEND_TO_OLD_LOG_FILE;
 #if BUILDFLAG(IS_CHROMEOS)
   // Contains an optional file that logs should be written to. If present,
   // |log_file_path| will be ignored, and the logging system will take ownership
   // of the FILE. If there's an error writing to this file, no fallback paths
   // will be opened.
   FILE* log_file = nullptr;
   // ChromeOS uses the syslog log format by default.
   LogFormat log_format = LogFormat::LOG_FORMAT_SYSLOG;
 #endif
 };

 // Define different names for the BaseInitLoggingImpl() function depending on
 // whether NDEBUG is defined or not so that we'll fail to link if someone tries
 // to compile logging.cc with NDEBUG but includes logging.h without defining it,
 // or vice versa.
 #if defined(NDEBUG)
 #define BaseInitLoggingImpl BaseInitLoggingImpl_built_with_NDEBUG
 #else
 #define BaseInitLoggingImpl BaseInitLoggingImpl_built_without_NDEBUG
 #endif

 // Implementation of the InitLogging() method declared below.  We use a
 // more-specific name so we can #define it above without affecting other code
 // that has named stuff "InitLogging".
 BASE_EXPORT bool BaseInitLoggingImpl(const LoggingSettings& settings);

 // Sets the log file name and other global logging state. Calling this function
 // is recommended, and is normally done at the beginning of application init.
 // If you don't call it, all the flags will be initialized to their default
 // values, and there is a race condition that may leak a critical section
 // object if two threads try to do the first log at the same time.
 // See the definition of the enums above for descriptions and default values.
 //
 // The default log file is initialized to "debug.log" in the application
 // directory. You probably don't want this, especially since the program
 // directory may not be writable on an enduser's system.
 //
 // This function may be called a second time to re-direct logging (e.g after
 // loging in to a user partition), however it should never be called more than
 // twice.
 inline bool InitLogging(const LoggingSettings& settings) {
   return BaseInitLoggingImpl(settings);
 }

 // Sets the log level. Anything at or above this level will be written to the
 // log file/displayed to the user (if applicable). Anything below this level
 // will be silently ignored. The log level defaults to 0 (everything is logged
 // up to level INFO) if this function is not called.
 // Note that log messages for VLOG(x) are logged at level -x, so setting
 // the min log level to negative values enables verbose logging and conversely,
 // setting the VLOG default level will set this min level to a negative number,
 // effectively enabling all levels of logging.
 BASE_EXPORT void SetMinLogLevel(int level);

 // Gets the current log level.
 BASE_EXPORT int GetMinLogLevel();

 // Used by LOG_IS_ON to lazy-evaluate stream arguments.
 BASE_EXPORT bool ShouldCreateLogMessage(int severity);

 // Gets the VLOG default verbosity level.
 BASE_EXPORT int GetVlogVerbosity();

 // Note that |N| is the size *with* the null terminator.
 BASE_EXPORT int GetVlogLevelHelper(const char* file_start, size_t N);

 // Gets the current vlog level for the given file (usually taken from __FILE__).
 template <size_t N>
 int GetVlogLevel(const char (&file)[N]) {
   return GetVlogLevelHelper(file, N);
 }

 // Sets the common items you want to be prepended to each log message.
 // process and thread IDs default to off, the timestamp defaults to on.
 // If this function is not called, logging defaults to writing the timestamp
 // only.
 BASE_EXPORT void SetLogItems(bool enable_process_id, bool enable_thread_id,
                              bool enable_timestamp, bool enable_tickcount);

 // Sets an optional prefix to add to each log message. |prefix| is not copied
 // and should be a raw string constant. |prefix| must only contain ASCII letters
 // to avoid confusion with PIDs and timestamps. Pass null to remove the prefix.
 // Logging defaults to no prefix.
 BASE_EXPORT void SetLogPrefix(const char* prefix);

 // Sets whether or not you'd like to see fatal debug messages popped up in
 // a dialog box or not.
 // Dialogs are not shown by default.
 BASE_EXPORT void SetShowErrorDialogs(bool enable_dialogs);

 // Sets the Log Assert Handler that will be used to notify of check failures.
 // Resets Log Assert Handler on object destruction.
 // The default handler shows a dialog box and then terminate the process,
 // however clients can use this function to override with their own handling
 // (e.g. a silent one for Unit Tests)
 using LogAssertHandlerFunction =
     base::RepeatingCallback<void(const char* file,
                                  int line,
                                  const base::StringPiece message,
                                  const base::StringPiece stack_trace)>;

 class BASE_EXPORT ScopedLogAssertHandler {
  public:
   explicit ScopedLogAssertHandler(LogAssertHandlerFunction handler);
   ScopedLogAssertHandler(const ScopedLogAssertHandler&) = delete;
   ScopedLogAssertHandler& operator=(const ScopedLogAssertHandler&) = delete;
   ~ScopedLogAssertHandler();
 };

 // Sets the Log Message Handler that gets passed every log message before
 // it's sent to other log destinations (if any).
 // Returns true to signal that it handled the message and the message
 // should not be sent to other log destinations.
 typedef bool (*LogMessageHandlerFunction)(int severity,
     const char* file, int line, size_t message_start, const std::string& str);
 BASE_EXPORT void SetLogMessageHandler(LogMessageHandlerFunction handler);
 BASE_EXPORT LogMessageHandlerFunction GetLogMessageHandler();

 using LogSeverity = int;
 constexpr LogSeverity LOGGING_VERBOSE = -1;  // This is level 1 verbosity
 // Note: the log severities are used to index into the array of names,
 // see log_severity_names.
 constexpr LogSeverity LOGGING_INFO = 0;
 constexpr LogSeverity LOGGING_WARNING = 1;
 constexpr LogSeverity LOGGING_ERROR = 2;
 constexpr LogSeverity LOGGING_FATAL = 3;
 constexpr LogSeverity LOGGING_NUM_SEVERITIES = 4;

 // LOGGING_DFATAL is LOGGING_FATAL in DCHECK-enabled builds, ERROR in normal
 // mode.
 #if DCHECK_IS_ON()
 constexpr LogSeverity LOGGING_DFATAL = LOGGING_FATAL;
 #else
 constexpr LogSeverity LOGGING_DFATAL = LOGGING_ERROR;
 #endif

 // This block duplicates the above entries to facilitate incremental conversion
 // from LOG_FOO to LOGGING_FOO.
 // TODO(thestig): Convert existing users to LOGGING_FOO and remove this block.
 constexpr LogSeverity LOG_VERBOSE = LOGGING_VERBOSE;
 constexpr LogSeverity LOG_INFO = LOGGING_INFO;
 constexpr LogSeverity LOG_WARNING = LOGGING_WARNING;
 constexpr LogSeverity LOG_ERROR = LOGGING_ERROR;
 constexpr LogSeverity LOG_FATAL = LOGGING_FATAL;
 constexpr LogSeverity LOG_DFATAL = LOGGING_DFATAL;

 // A few definitions of macros that don't generate much code. These are used
 // by LOG() and LOG_IF, etc. Since these are used all over our code, it's
 // better to have compact code for these operations.
 #define COMPACT_GOOGLE_LOG_EX_INFO(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_INFO, \
                        ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_EX_WARNING(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_WARNING, \
                        ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_EX_ERROR(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_ERROR, \
                        ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_EX_FATAL(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_FATAL, \
                        ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_EX_DFATAL(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_DFATAL, \
                        ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...)                  \
   ::logging::ClassName(__FILE__, __LINE__, ::logging::LOGGING_DCHECK, \
                        ##__VA_ARGS__)

 #define COMPACT_GOOGLE_LOG_INFO COMPACT_GOOGLE_LOG_EX_INFO(LogMessage)
 #define COMPACT_GOOGLE_LOG_WARNING COMPACT_GOOGLE_LOG_EX_WARNING(LogMessage)
 #define COMPACT_GOOGLE_LOG_ERROR COMPACT_GOOGLE_LOG_EX_ERROR(LogMessage)
 #define COMPACT_GOOGLE_LOG_FATAL COMPACT_GOOGLE_LOG_EX_FATAL(LogMessage)
 #define COMPACT_GOOGLE_LOG_DFATAL COMPACT_GOOGLE_LOG_EX_DFATAL(LogMessage)
 #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_EX_DCHECK(LogMessage)

 #if BUILDFLAG(IS_WIN)
 // wingdi.h defines ERROR to be 0. When we call LOG(ERROR), it gets
 // substituted with 0, and it expands to COMPACT_GOOGLE_LOG_0. To allow us
 // to keep using this syntax, we define this macro to do the same thing
 // as COMPACT_GOOGLE_LOG_ERROR, and also define ERROR the same way that
 // the Windows SDK does for consistency.
 #define ERROR 0
 #define COMPACT_GOOGLE_LOG_EX_0(ClassName, ...) \
   COMPACT_GOOGLE_LOG_EX_ERROR(ClassName , ##__VA_ARGS__)
 #define COMPACT_GOOGLE_LOG_0 COMPACT_GOOGLE_LOG_ERROR
 // Needed for LOG_IS_ON(ERROR).
 constexpr LogSeverity LOGGING_0 = LOGGING_ERROR;
 #endif

 // As special cases, we can assume that LOG_IS_ON(FATAL) always holds. Also,
 // LOG_IS_ON(DFATAL) always holds in debug mode. In particular, CHECK()s will
 // always fire if they fail.
 #define LOG_IS_ON(severity) \
   (::logging::ShouldCreateLogMessage(::logging::LOGGING_##severity))

 #if !BUILDFLAG(USE_RUNTIME_VLOG)

 // When USE_RUNTIME_VLOG is not set, --vmodule is completely ignored and
 // ENABLED_VLOG_LEVEL macro is used to determine the enabled VLOG levels
 // at build time.
 //
 // Files that need VLOG would need to redefine ENABLED_VLOG_LEVEL to a desired
 // VLOG level number,
 // e.g.
 //   To enable VLOG(1) output,
 //
 //   For a source cc file:
 //
 //     #undef ENABLED_VLOG_LEVEL
 //     #define ENABLED_VLOG_LEVEL 1
 //
 //   For all cc files in a build target of a BUILD.gn:
 //
 //     source_set("build_target") {
 //       ...
 //
 //       defines = ["ENABLED_VLOG_LEVEL=1"]
 //     }

 // Returns a vlog level that suppresses all vlogs. Using this function so that
 // compiler cannot calculate VLOG_IS_ON() and generate unreached code
 // warnings.
 BASE_EXPORT int GetDisableAllVLogLevel();

 // Define the default ENABLED_VLOG_LEVEL if it is not defined. This is to
 // allow ENABLED_VLOG_LEVEL to be overridden from defines in cc flags.
 #if !defined(ENABLED_VLOG_LEVEL)
 #define ENABLED_VLOG_LEVEL (logging::GetDisableAllVLogLevel())
 #endif  // !defined(ENABLED_VLOG_LEVEL)

 #define VLOG_IS_ON(verboselevel) ((verboselevel) <= (ENABLED_VLOG_LEVEL))

 #else  // !BUILDFLAG(USE_RUNTIME_VLOG)

 // We don't do any caching tricks with VLOG_IS_ON() like the
 // google-glog version since it increases binary size.  This means
 // that using the v-logging functions in conjunction with --vmodule
 // may be slow.

 #define VLOG_IS_ON(verboselevel) \
   ((verboselevel) <= ::logging::GetVlogLevel(__FILE__))

 #endif  // !BUILDFLAG(USE_RUNTIME_VLOG)

 // Helper macro which avoids evaluating the arguments to a stream if
 // the condition doesn't hold. Condition is evaluated once and only once.
 #define LAZY_STREAM(stream, condition)                                  \
   !(condition) ? (void) 0 : ::logging::LogMessageVoidify() & (stream)

 // We use the preprocessor's merging operator, "##", so that, e.g.,
 // LOG(INFO) becomes the token COMPACT_GOOGLE_LOG_INFO.  There's some funny
 // subtle difference between ostream member streaming functions (e.g.,
 // ostream::operator<<(int) and ostream non-member streaming functions
 // (e.g., ::operator<<(ostream&, string&): it turns out that it's
 // impossible to stream something like a string directly to an unnamed
 // ostream. We employ a neat hack by calling the stream() member
 // function of LogMessage which seems to avoid the problem.
 #define LOG_STREAM(severity) COMPACT_GOOGLE_LOG_ ## severity.stream()

 #define LOG(severity) LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity))
 #define LOG_IF(severity, condition) \
   LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity) && (condition))

 // The VLOG macros log with negative verbosities.
 #define VLOG_STREAM(verbose_level) \
   ::logging::LogMessage(__FILE__, __LINE__, -(verbose_level)).stream()

 #define VLOG(verbose_level) \
   LAZY_STREAM(VLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))

 #define VLOG_IF(verbose_level, condition) \
   LAZY_STREAM(VLOG_STREAM(verbose_level), \
       VLOG_IS_ON(verbose_level) && (condition))

 #if BUILDFLAG(IS_WIN)
 #define VPLOG_STREAM(verbose_level) \
   ::logging::Win32ErrorLogMessage(__FILE__, __LINE__, -(verbose_level), \
     ::logging::GetLastSystemErrorCode()).stream()
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 #define VPLOG_STREAM(verbose_level) \
   ::logging::ErrnoLogMessage(__FILE__, __LINE__, -(verbose_level), \
     ::logging::GetLastSystemErrorCode()).stream()
 #endif

 #define VPLOG(verbose_level) \
   LAZY_STREAM(VPLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))

 #define VPLOG_IF(verbose_level, condition) \
   LAZY_STREAM(VPLOG_STREAM(verbose_level), \
     VLOG_IS_ON(verbose_level) && (condition))

 // TODO(akalin): Add more VLOG variants, e.g. VPLOG.

 #define LOG_ASSERT(condition)                       \
   LOG_IF(FATAL, !(ANALYZER_ASSUME_TRUE(condition))) \
       << "Assert failed: " #condition ". "

 #if BUILDFLAG(IS_WIN)
 #define PLOG_STREAM(severity) \
   COMPACT_GOOGLE_LOG_EX_ ## severity(Win32ErrorLogMessage, \
       ::logging::GetLastSystemErrorCode()).stream()
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 #define PLOG_STREAM(severity) \
   COMPACT_GOOGLE_LOG_EX_ ## severity(ErrnoLogMessage, \
       ::logging::GetLastSystemErrorCode()).stream()
 #endif

 #define PLOG(severity)                                          \
   LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity))

 #define PLOG_IF(severity, condition) \
   LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity) && (condition))

 BASE_EXPORT extern std::ostream* g_swallow_stream;

 // Note that g_swallow_stream is used instead of an arbitrary LOG() stream to
 // avoid the creation of an object with a non-trivial destructor (LogMessage).
 // On MSVC x86 (checked on 2015 Update 3), this causes a few additional
 // pointless instructions to be emitted even at full optimization level, even
 // though the : arm of the ternary operator is clearly never executed. Using a
 // simpler object to be &'d with Voidify() avoids these extra instructions.
 // Using a simpler POD object with a templated operator<< also works to avoid
 // these instructions. However, this causes warnings on statically defined
 // implementations of operator<<(std::ostream, ...) in some .cc files, because
 // they become defined-but-unreferenced functions. A reinterpret_cast of 0 to an
 // ostream* also is not suitable, because some compilers warn of undefined
 // behavior.
 #define EAT_STREAM_PARAMETERS \
   true ? (void)0              \
        : ::logging::LogMessageVoidify() & (*::logging::g_swallow_stream)

 // Definitions for DLOG et al.

 #if DCHECK_IS_ON()

 #define DLOG_IS_ON(severity) LOG_IS_ON(severity)
 #define DLOG_IF(severity, condition) LOG_IF(severity, condition)
 #define DLOG_ASSERT(condition) LOG_ASSERT(condition)
 #define DPLOG_IF(severity, condition) PLOG_IF(severity, condition)
 #define DVLOG_IF(verboselevel, condition) VLOG_IF(verboselevel, condition)
 #define DVPLOG_IF(verboselevel, condition) VPLOG_IF(verboselevel, condition)

 #else  // DCHECK_IS_ON()

 // If !DCHECK_IS_ON(), we want to avoid emitting any references to |condition|
 // (which may reference a variable defined only if DCHECK_IS_ON()).
 // Contrast this with DCHECK et al., which has different behavior.

 #define DLOG_IS_ON(severity) false
 #define DLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
 #define DLOG_ASSERT(condition) EAT_STREAM_PARAMETERS
 #define DPLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
 #define DVLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS
 #define DVPLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS

 #endif  // DCHECK_IS_ON()

 #define DLOG(severity)                                          \
   LAZY_STREAM(LOG_STREAM(severity), DLOG_IS_ON(severity))

 #define DPLOG(severity)                                         \
   LAZY_STREAM(PLOG_STREAM(severity), DLOG_IS_ON(severity))

 #define DVLOG(verboselevel) DVLOG_IF(verboselevel, true)

 #define DVPLOG(verboselevel) DVPLOG_IF(verboselevel, true)

 // Definitions for DCHECK et al.

 #if BUILDFLAG(DCHECK_IS_CONFIGURABLE)
 BASE_EXPORT extern LogSeverity LOGGING_DCHECK;
 #else
 constexpr LogSeverity LOGGING_DCHECK = LOGGING_FATAL;
 #endif  // BUILDFLAG(DCHECK_IS_CONFIGURABLE)

 // Redefine the standard assert to use our nice log files
 #undef assert
 #define assert(x) DLOG_ASSERT(x)

 // This class more or less represents a particular log message.  You
 // create an instance of LogMessage and then stream stuff to it.
 // When you finish streaming to it, ~LogMessage is called and the
 // full message gets streamed to the appropriate destination.
 //
 // You shouldn't actually use LogMessage's constructor to log things,
 // though.  You should use the LOG() macro (and variants thereof)
 // above.
 class BASE_EXPORT LogMessage {
  public:
   // Used for LOG(severity).
   LogMessage(const char* file, int line, LogSeverity severity);

   // Used for CHECK().  Implied severity = LOGGING_FATAL.
   LogMessage(const char* file, int line, const char* condition);
   LogMessage(const LogMessage&) = delete;
   LogMessage& operator=(const LogMessage&) = delete;
   virtual ~LogMessage();

   std::ostream& stream() { return stream_; }

   LogSeverity severity() const { return severity_; }
   std::string str() const { return stream_.str(); }
   const char* file() const { return file_; }
   int line() const { return line_; }

   // Gets file:line: message in a format suitable for crash reporting.
   std::string BuildCrashString() const;

  private:
   void Init(const char* file, int line);

   const LogSeverity severity_;
   std::ostringstream stream_;
   size_t message_start_;  // Offset of the start of the message (past prefix
                           // info).
   // The file and line information passed in to the constructor.
   const char* const file_;
   const int line_;

   // This is useful since the LogMessage class uses a lot of Win32 calls
   // that will lose the value of GLE and the code that called the log function
   // will have lost the thread error value when the log call returns.
   base::ScopedClearLastError last_error_;

 #if BUILDFLAG(IS_CHROMEOS)
   void InitWithSyslogPrefix(base::StringPiece filename,
                             int line,
                             uint64_t tick_count,
                             const char* log_severity_name_c_str,
                             const char* log_prefix,
                             bool enable_process_id,
                             bool enable_thread_id,
                             bool enable_timestamp,
                             bool enable_tickcount);
 #endif
 };

 // This class is used to explicitly ignore values in the conditional
 // logging macros.  This avoids compiler warnings like "value computed
 // is not used" and "statement has no effect".
 class LogMessageVoidify {
  public:
   LogMessageVoidify() = default;
   // This has to be an operator with a precedence lower than << but
   // higher than ?:
   void operator&(std::ostream&) { }
 };

 #if BUILDFLAG(IS_WIN)
 typedef unsigned long SystemErrorCode;
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 typedef int SystemErrorCode;
 #endif

 // Alias for ::GetLastError() on Windows and errno on POSIX. Avoids having to
 // pull in windows.h just for GetLastError() and DWORD.
 BASE_EXPORT SystemErrorCode GetLastSystemErrorCode();
 BASE_EXPORT std::string SystemErrorCodeToString(SystemErrorCode error_code);

 #if BUILDFLAG(IS_WIN)
 // Appends a formatted system message of the GetLastError() type.
 class BASE_EXPORT Win32ErrorLogMessage : public LogMessage {
  public:
   Win32ErrorLogMessage(const char* file,
                        int line,
                        LogSeverity severity,
                        SystemErrorCode err);
   Win32ErrorLogMessage(const Win32ErrorLogMessage&) = delete;
   Win32ErrorLogMessage& operator=(const Win32ErrorLogMessage&) = delete;
   // Appends the error message before destructing the encapsulated class.
   ~Win32ErrorLogMessage() override;

  private:
   SystemErrorCode err_;
 };
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 // Appends a formatted system message of the errno type
 class BASE_EXPORT ErrnoLogMessage : public LogMessage {
  public:
   ErrnoLogMessage(const char* file,
                   int line,
                   LogSeverity severity,
                   SystemErrorCode err);
   ErrnoLogMessage(const ErrnoLogMessage&) = delete;
   ErrnoLogMessage& operator=(const ErrnoLogMessage&) = delete;
   // Appends the error message before destructing the encapsulated class.
   ~ErrnoLogMessage() override;

  private:
   SystemErrorCode err_;
 };
 #endif  // BUILDFLAG(IS_WIN)

 // Closes the log file explicitly if open.
 // NOTE: Since the log file is opened as necessary by the action of logging
 //       statements, there's no guarantee that it will stay closed
 //       after this call.
 BASE_EXPORT void CloseLogFile();

 #if BUILDFLAG(IS_CHROMEOS_ASH)
 // Returns a new file handle that will write to the same destination as the
 // currently open log file. Returns nullptr if logging to a file is disabled,
 // or if opening the file failed. This is intended to be used to initialize
 // logging in child processes that are unable to open files.
 BASE_EXPORT FILE* DuplicateLogFILE();
 #endif

 // Async signal safe logging mechanism.
 BASE_EXPORT void RawLog(int level, const char* message);

 #define RAW_LOG(level, message) \
   ::logging::RawLog(::logging::LOGGING_##level, message)

 #if BUILDFLAG(IS_WIN)
 // Returns true if logging to file is enabled.
 BASE_EXPORT bool IsLoggingToFileEnabled();

 // Returns the default log file path.
 BASE_EXPORT std::wstring GetLogFileFullPath();
 #endif

 }  // namespace logging

 #endif  // BASE_LOGGING_H_