racket/gui Gtk: choice% and combo% repair for some Gtk variants

Finishes repair started in 8cbcba8ed so that mouse events can be
intercepted for `combo%` and `choice%` objects. DrRacket's
font preference choice relies on intercepting mouse events
to populate the menu, for example.

Reference counting doesn't seem to work, probably because the
relevant widgets are supposed to be private.

pkgs/gui-pkgs/gui-lib/mred/private/wx/gtk/canvas.rkt

@@ -242,7 +242,8 @@
               is-auto-scroll? is-disabled-scroll?
               get-virtual-width get-virtual-height
               refresh-for-autoscroll refresh-all-children
-              get-eventspace)
+              get-eventspace
+	      register-extra-gtk)
 
      (define is-combo? (memq 'combo style))
      (define has-border? (or (memq 'border style)
@@ -359,6 +360,10 @@
                                          (list client-gtk combo-button-gtk)
                                          (list client-gtk)))))])
 
+     (define/private (check-combo)
+       (when is-combo?
+	 (set! combo-button-gtk (re-extract-combo-button gtk combo-button-gtk this))))
+
      (set-size x y w h)
 
      (define/override (set-size x y w h)
@@ -393,6 +398,7 @@
                  (is-panel?))
        (set-gtk-object-flags! client-gtk (bitwise-ior (get-gtk-object-flags client-gtk)
                                                       GTK_CAN_FOCUS)))
+     (check-combo)
      (when combo-button-gtk
        (connect-combo-key-and-mouse combo-button-gtk))
      (connect-unrealize client-gtk)

pkgs/gui-pkgs/gui-lib/mred/private/wx/gtk/choice.rkt

@@ -59,6 +59,7 @@
   (set-auto-size)
 
   (connect-changed gtk)
+  (set! button-gtk (re-extract-combo-button gtk button-gtk this))
   (connect-focus button-gtk)
   (connect-combo-key-and-mouse button-gtk)
 

pkgs/gui-pkgs/gui-lib/mred/private/wx/gtk/combo.rkt

@@ -10,6 +10,7 @@
 
 (provide 
  (protect-out extract-combo-button
+	      re-extract-combo-button
               connect-combo-key-and-mouse))
 
 ;; ----------------------------------------
@@ -17,6 +18,8 @@
 (define-gtk gtk_container_foreach (_fun _GtkWidget (_fun _GtkWidget -> _void) _pointer -> _void))
 (define-gtk gtk_container_forall (_fun _GtkWidget (_fun _GtkWidget -> _void) _pointer -> _void))
 
+(define-gtk gtk_widget_get_name (_fun _GtkWidget -> _string))
+
 (define-gobj g_signal_parse_name (_fun _string
                                        _GType
                                        (id : (_ptr o _uint))
@@ -80,17 +83,39 @@
     (gtk_container_forall gtk (lambda (c) (set! all (cons c all))) #f)
     (gtk_container_foreach gtk (lambda (c) (set! ext (cons c ext))) #f)
     (for-each (lambda (e)
-                (set! all (filter (lambda (a) (not (ptr-equal? a e)))
+                (set! all (filter (lambda (a)
+				    (not (ptr-equal? a e)))
                                   all)))
               ext)
-    (unless (= 1 (length all))
-      (error "expected Gtk combobox to have one private child"))
-    (define combo-gtk (car all))
-    (gobject-ref combo-gtk)
+    (define combo-gtk
+      (cond
+       [(= 1 (length all))
+	;; most common case:
+	(car all)]
+       [(and (= 2 (length all))
+	     (equal? '("GtkFrame" "GtkToggleButton")
+		     (map gtk_widget_get_name all)))
+	(define inner null)
+	(gtk_container_forall (car all) (lambda (c) (set! inner (cons c inner))) #f)
+	(and (= 1 (length inner))
+	     (car inner))]
+       [else #f]))
+    (unless combo-gtk
+      (error "unrecognized Gtk combobox implementation"))
     combo-gtk))
 
+(define (re-extract-combo-button gtk combo-button-gtk win)
+  (define c-gtk (extract-combo-button gtk))
+  (cond
+   [(ptr-equal? c-gtk combo-button-gtk)
+    ;; combo button hasn't changed:
+    combo-button-gtk]
+   [else
+    (send win register-extra-gtk gtk c-gtk)
+    c-gtk]))
+
 ;; More dependence on the implemenation of GtkComboBox:
-;; The memnu-popup action is implemented by seeting a button-press-event
+;; The menu-popup action is implemented by seeting a button-press-event
 ;; signal handler on `button-gtk'. Since Gtk calls signal handlers in the
 ;; order that they're registered, our button-press-event handler doesn't
 ;; get called first, so it can't cancel the button press due to modality

pkgs/gui-pkgs/gui-lib/mred/private/wx/gtk/widget.rkt

@@ -57,6 +57,10 @@
     
     (super-new)
 
+    (define/public (register-extra-gtk gtk extra-gtk)
+      (define cell (g_object_get_data gtk "wx"))
+      (g_object_set_data extra-gtk "wx" cell))
+
     (atomically
      (let ([cell (malloc-immobile-cell (make-weak-box this))])
        (g_object_set_data gtk "wx" cell)