Support GUI dialogs and message boxes better on MS-Windows

* src/w32menu.c (TASKDIALOG_COMMON_BUTTON_FLAGS, TASKDIALOG_FLAGS)
(PFTASKDIALOGCALLBACK, TASKDIALOG_BUTTON, TASKDIALOGCONFIG)
(TDN_CREATED, TDM_ENABLE_BUTTON, TDF_ALLOW_DIALOG_CANCELLATION)
(TD_INFORMATION_ICON) [!MINGW_W64]: Define.
(TaskDialogIndirect_Proc): Declare function type.
(TASK_DIALOG_MAX_BUTTONS): New macro.
(task_dialog_callback): New callback function.
(w32_popup_dialog): Add dialog implementation using TaskDialog.
(globals_of_w32menu): Load TaskDialogIndirect from comctl32.dll.
(Bug#20481)

1 files changed, 4 insertions, 3 deletions

diff --git a/src/menu.c b/src/menu.c
index de4d0964e9c..6b4aaef1715 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -1594,9 +1594,10 @@ for instance using the window manager, then this produces a quit and
       Lisp_Object selection
         = FRAME_TERMINAL (f)->popup_dialog_hook (f, header, contents);
 #ifdef HAVE_NTGUI
-      /* NTGUI supports only simple dialogs with Yes/No choices.  For
-         other dialogs, it returns the symbol 'unsupported--w32-dialog',
-         as a signal for the caller to fall back to the emulation code.  */
+      /* NTGUI on Windows versions before Vista supports only simple
+         dialogs with Yes/No choices.  For other dialogs, it returns the
+         symbol 'unsupported--w32-dialog', as a signal for the caller to
+         fall back to the emulation code.  */
       if (!EQ (selection, Qunsupported__w32_dialog))
 #endif
         return selection;