qt_sink: add some warning on its usage (#2753)

* qt_sink: add some warning on its usage

* qt_sink: add some warning on its usage - fix

---------

Co-authored-by: Benoit FANCHON <bfanchon@nanoxplore.com>

include/spdlog/sinks/qt_sinks.h

@@ -55,25 +55,35 @@ private:
 
 #include "spdlog/details/null_mutex.h"
 #include <mutex>
+// Warning: qt_sink won't be notified if the target QObject is destroyed.
+// If the object's lifetime can be shorter than the logger's one, you should provide some permanent object and then use a standard signal/slot.
 using qt_sink_mt = qt_sink<std::mutex>;
+// Warning: qt_sink won't be notified if the target QObject is destroyed.
+// If the object's lifetime can be shorter than the logger's one, you should provide some permanent object and then use a standard signal/slot.
 using qt_sink_st = qt_sink<spdlog::details::null_mutex>;
 } // namespace sinks
 
 //
 // Factory functions
 //
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(const std::string &logger_name, QTextEdit *qt_object, const std::string &meta_method = "append")
 {
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(const std::string &logger_name, QTextEdit *qt_object, const std::string &meta_method = "append")
 {
     return Factory::template create<sinks::qt_sink_st>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the object's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(
     const std::string &logger_name, QPlainTextEdit *qt_object, const std::string &meta_method = "appendPlainText")
@@ -81,6 +91,8 @@ inline std::shared_ptr<logger> qt_logger_mt(
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target widget is destroyed.
+// If the widget's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(
     const std::string &logger_name, QPlainTextEdit *qt_object, const std::string &meta_method = "appendPlainText")
@@ -88,12 +100,16 @@ inline std::shared_ptr<logger> qt_logger_st(
     return Factory::template create<sinks::qt_sink_st>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the objet's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_mt(const std::string &logger_name, QObject *qt_object, const std::string &meta_method)
 {
     return Factory::template create<sinks::qt_sink_mt>(logger_name, qt_object, meta_method);
 }
 
+// Warning: the qt_sink won't be notified if the target QObject is destroyed.
+// If the objet's lifetime can be shorter than the logger's one, you should provide some permanent QObject and then use a standard signal/slot.
 template<typename Factory = spdlog::synchronous_factory>
 inline std::shared_ptr<logger> qt_logger_st(const std::string &logger_name, QObject *qt_object, const std::string &meta_method)
 {