Fix bug #16636 with simple dialogs on MS-Windows.

 src/w32menu.c (w32_popup_dialog): Don't condition the whole function
 on HAVE_DIALOGS.  If the dialog is "simple", pop up a message box
 to show it; otherwise return 'unsupported--w32-dialog' to signal
 to the caller that emulation with menus is necessary.  This
 resurrects code inadvertently deleted by the 2013-10-08 commit.
 (syms_of_w32menu): DEFSYM Qunsupported__w32_dialog.
 src/w32term.h (w32_popup_dialog): Prototype is no longer conditioned
 by HAVE_DIALOGS.
 src/menu.c (Fx_popup_dialog): Don't condition the call to
 w32_popup_dialog on HAVE_DIALOGS.  If w32_popup_dialog returns a
 special symbol 'unsupported--w32-dialog', emulate the dialog with
 a menu by calling x-popup-menu.
 src/menu.h (Qunsupported__w32_dialog): New extern variable.

1 files changed, 10 insertions, 2 deletions

diff --git a/src/menu.c b/src/menu.c
index c38152f47e8..47ebc922b84 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -1566,9 +1566,15 @@ for instance using the window manager, then this produces a quit and
     return xw_popup_dialog (f, header, contents);
   else
 #endif
-#if defined (HAVE_NTGUI) && defined (HAVE_DIALOGS)
+#if defined (HAVE_NTGUI)
   if (FRAME_W32_P (f))
-    return w32_popup_dialog (f, header, contents);
+    {
+      Lisp_Object selection = w32_popup_dialog (f, header, contents);
+
+      if (!EQ (selection, Qunsupported__w32_dialog))
+        return selection;
+      goto dialog_via_menu;
+    }
   else
 #endif
 #ifdef HAVE_NS
@@ -1582,6 +1588,8 @@ for instance using the window manager, then this produces a quit and
     Lisp_Object x, y, frame, newpos, prompt;
     int x_coord, y_coord;
 
+  dialog_via_menu:
+
     prompt = Fcar (contents);
     if (FRAME_WINDOW_P (f))
       {