QLogging: simplify qDefaultMessageHandler() with a global constant

Namely, a function pointer to the actual sink function.

This doesn't remove the future ability to iterate over multiple sinks,
but I removed the comment anyway because it doesn't look like we'll ever
implement that.

Change-Id: Ifa1111900d6945ea8e05fffd177de7fa46230259
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

2 files changed, 35 insertions, 26 deletions

diff --git a/src/corelib/global/qlogging.cpp b/src/corelib/global/qlogging.cpp
index 3f0cb67989..bb8706bcac 100644
--- a/src/corelib/global/qlogging.cpp
+++ b/src/corelib/global/qlogging.cpp
@@ -1901,40 +1901,46 @@ static void stderr_message_handler(QtMsgType type, const QMessageLogContext &con
     fflush(stderr);
 }
 
+using SystemMessageSink = bool(QtMsgType, const QMessageLogContext &, const QString &);
+static constexpr SystemMessageSink *systemMessageSink =
+#if defined(QT_BOOTSTRAPPED)
+        nullptr
+#elif defined(Q_OS_WIN)
+        win_message_handler
+#elif QT_CONFIG(slog2)
+        slog2_default_handler
+#elif QT_CONFIG(journald)
+        systemd_default_message_handler
+#elif QT_CONFIG(syslog)
+        syslog_default_message_handler
+#elif defined(Q_OS_ANDROID)
+        android_default_message_handler
+#elif defined(QT_USE_APPLE_UNIFIED_LOGGING)
+        AppleUnifiedLogger::messageHandler
+#elif defined Q_OS_WASM
+        wasm_default_message_handler
+#else
+        nullptr
+#endif
+        ;
+
 /*!
     \internal
 */
 static void qDefaultMessageHandler(QtMsgType type, const QMessageLogContext &context,
                                    const QString &message)
 {
-    bool handledStderr = false;
-
     // A message sink logs the message to a structured or unstructured destination,
     // optionally formatting the message if the latter, and returns true if the sink
     // handled stderr output as well, which will shortcut our default stderr output.
-    // In the future, if we allow multiple/dynamic sinks, this will be iterating
-    // a list of sinks.
-
-#if !defined(QT_BOOTSTRAPPED)
-# if defined(Q_OS_WIN)
-    handledStderr |= win_message_handler(type, context, message);
-# elif QT_CONFIG(slog2)
-    handledStderr |= slog2_default_handler(type, context, message);
-# elif QT_CONFIG(journald)
-    handledStderr |= systemd_default_message_handler(type, context, message);
-# elif QT_CONFIG(syslog)
-    handledStderr |= syslog_default_message_handler(type, context, message);
-# elif defined(Q_OS_ANDROID)
-    handledStderr |= android_default_message_handler(type, context, message);
-# elif defined(QT_USE_APPLE_UNIFIED_LOGGING)
-    handledStderr |= AppleUnifiedLogger::messageHandler(type, context, message);
-# elif defined Q_OS_WASM
-    handledStderr |= wasm_default_message_handler(type, context, message);
-# endif
-#endif
 
-    if (!handledStderr)
-        stderr_message_handler(type, context, message);
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_GCC("-Waddress") // "the address of ~~ will never be NULL
+    if (systemMessageSink && systemMessageSink(type, context, message))
+        return;
+QT_WARNING_POP
+
+    stderr_message_handler(type, context, message);
 }
 
 #if defined(Q_COMPILER_THREAD_LOCAL)
diff --git a/src/corelib/kernel/qcore_mac_p.h b/src/corelib/kernel/qcore_mac_p.h
index 1b0283e77b..495d0df13f 100644
--- a/src/corelib/kernel/qcore_mac_p.h
+++ b/src/corelib/kernel/qcore_mac_p.h
@@ -236,8 +236,11 @@ QT_BEGIN_NAMESPACE
 class Q_CORE_EXPORT AppleUnifiedLogger
 {
 public:
-    static bool messageHandler(QtMsgType msgType, const QMessageLogContext &context, const QString &message,
-        const QString &subsystem = QString());
+    static bool messageHandler(QtMsgType msgType, const QMessageLogContext &context,
+                               const QString &message)
+    { return messageHandler(msgType, context, message, QString()); }
+    static bool messageHandler(QtMsgType msgType, const QMessageLogContext &context,
+                               const QString &message, const QString &subsystem);
     static bool preventsStderrLogging();
 private:
     static os_log_type_t logTypeForMessageType(QtMsgType msgType);