From c3810da54937110df8a5cfc3aee66fde2960b593 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Thu, 9 Apr 2020 19:48:59 +0200
Subject: [PATCH] Allow using noexcept methods with event tables macros

Explicitly remove noexcept before static-casting the member function
pointer to the base class pointer type to avoid compilation error with
C++17.

Add a test checking that this does work now.

Closes #18721.
---
 include/wx/event.h          | 36 +++++++++++++++++++++++++++++++++++-
 tests/events/evthandler.cpp |  7 +++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/include/wx/event.h b/include/wx/event.h
index 39ca40725d..1c9b794fd9 100644
--- a/include/wx/event.h
+++ b/include/wx/event.h
@@ -144,9 +144,43 @@ inline wxEventFunction wxEventFunctionCast(void (wxEvtHandler::*func)(T&))
     wxGCC_WARNING_RESTORE_CAST_FUNCTION_TYPE()
 }
 
+// Special hack to remove "noexcept" from the function type when using C++17 or
+// later: static_cast<> below would fail to cast a member function pointer to a
+// member of a derived class to the base class if noexcept is specified for the
+// former, so remove it first if necessary.
+#if __cplusplus >= 201703L
+
+namespace wxPrivate
+{
+
+// Generic template version, doing nothing.
+template <typename T>
+struct RemoveNoexceptEventHandler
+{
+    using type = T;
+};
+
+// Specialization removing noexcept when it's specified.
+//
+// Note that this doesn't pretend to be generally suitable, this is just enough
+// to work in our particular case.
+template <typename R, typename C, typename E>
+struct RemoveNoexceptEventHandler<R (C::*)(E&) noexcept>
+{
+    using type = R (C::*)(E&);
+};
+
+} // namespace wxPrivate
+
+#define wxREMOVE_NOEXCEPT_EVENT_HANDLER(pmf) \
+    static_cast<wxPrivate::RemoveNoexceptEventHandler<decltype(pmf)>::type>(pmf)
+#else
+#define wxREMOVE_NOEXCEPT_EVENT_HANDLER(pmf) pmf
+#endif
+
 // Try to cast the given event handler to the correct handler type:
 #define wxEVENT_HANDLER_CAST( functype, func ) \
-    wxEventFunctionCast(static_cast<functype>(&func))
+    wxEventFunctionCast(static_cast<functype>(wxREMOVE_NOEXCEPT_EVENT_HANDLER(&func)))
 
 
 // The tag is a type associated to the event type (which is an integer itself,
diff --git a/tests/events/evthandler.cpp b/tests/events/evthandler.cpp
index 6be6c2d1ec..dce3f762a5 100644
--- a/tests/events/evthandler.cpp
+++ b/tests/events/evthandler.cpp
@@ -122,6 +122,9 @@ public:
     void OnEvent(wxEvent&) { g_called.method = true; }
     void OnAnotherEvent(AnotherEvent&);
     void OnIdle(wxIdleEvent&) { g_called.method = true; }
+#ifdef wxHAS_NOEXCEPT
+    void OnIdleNoExcept(wxIdleEvent&) noexcept { }
+#endif
 
 private:
     wxDECLARE_EVENT_TABLE();
@@ -138,6 +141,10 @@ wxBEGIN_EVENT_TABLE(MyClassWithEventTable, wxEvtHandler)
     EVT_MYEVENT(MyClassWithEventTable::OnMyEvent)
     EVT_MYEVENT(MyClassWithEventTable::OnEvent)
 
+#ifdef wxHAS_NOEXCEPT
+    EVT_IDLE(MyClassWithEventTable::OnIdleNoExcept)
+#endif
+
     // this shouldn't compile:
     //EVT_MYEVENT(MyClassWithEventTable::OnIdle)
     //EVT_IDLE(MyClassWithEventTable::OnAnotherEvent)