[glib/th/gsignal-cleanup: 32/33] gsignal: let g_clear_signal_handler() evaluate argument only once

[Thomas Haller <thaller src gnome org>]

commit 7777f3bdbe7101b78ef94b262998e63f137abeb8
Author: Thomas Haller <thaller redhat com>
Date:   Tue Jan 26 14:09:02 2021 +0100

    gsignal: let g_clear_signal_handler() evaluate argument only once
    
    Preferably macros behave function-like to minimize surprises. That
    means for example that they evaluate all arguments exactly once.
    
    Rework g_clear_signal_handler() to assign the macro parameters
    to auto variables so they are accessed exactly once.
    
    Also, drop the static assert for the size of (*handler_id_ptr).
    As we now assign to a "gulong *" pointer, the compiler already
    checks the types. In fact, the check is now stricter than before.
    Previously it would have allowed a pointer to a "signed long".
    This is a change in behavior of the macro and the stricter compile
    check could cause a build failure with broken code.
    
    Also, clear the handler id first, before calling
    g_signal_handler_disconnect(). Disconnecting a signal invokes the
    destroy notify, which can have side effects. It just feels cleaner
    to first reset the *_handler_id_ptr, before those side effects
    can happen. Of course, in practice it makes little difference.

 gobject/gsignal.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/gobject/gsignal.h b/gobject/gsignal.h
index 536102dad..64aa9d6a8 100644
--- a/gobject/gsignal.h
+++ b/gobject/gsignal.h
@@ -451,13 +451,14 @@ void       g_clear_signal_handler               (gulong            *handler_id_ptr,
 
 #define  g_clear_signal_handler(handler_id_ptr, instance)           \
   G_STMT_START {                                                    \
-    G_STATIC_ASSERT (sizeof *(handler_id_ptr) == sizeof (gulong));  \
-    gulong _handler_id = *(handler_id_ptr);                         \
+    gpointer const _instance      = (instance);                     \
+    gulong *const _handler_id_ptr = (handler_id_ptr);               \
+    const gulong _handler_id      = *_handler_id_ptr;               \
                                                                     \
     if (_handler_id > 0)                                            \
       {                                                             \
-        g_signal_handler_disconnect ((instance), _handler_id);      \
-        *(handler_id_ptr) = 0;                                      \
+        *_handler_id_ptr = 0;                                       \
+        g_signal_handler_disconnect (_instance, _handler_id);       \
       }                                                             \
   } G_STMT_END                                                      \
   GLIB_AVAILABLE_MACRO_IN_2_62