[3.12] gh-120211: Fix tkinter.ttk with Tcl/Tk 9.0 (GH-120213) (GH-120216)

* Use new methods for tracing Tcl variable.
* Fix Combobox.current() for empty combobox.
(cherry picked from commit d68a22e7a6)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/tkinter/ttk.py

@@ -683,7 +683,10 @@ def current(self, newindex=None):
         returns the index of the current value in the list of values
         or -1 if the current value does not appear in the list."""
         if newindex is None:
-            return self.tk.getint(self.tk.call(self._w, "current"))
+            res = self.tk.call(self._w, "current")
+            if res == '':
+                return -1
+            return self.tk.getint(res)
         return self.tk.call(self._w, "current", newindex)
 
 
@@ -1515,7 +1518,7 @@ def __init__(self, master=None, variable=None, from_=0, to=10, **kw):
         self.label.place(anchor='n' if label_side == 'top' else 's')
 
         # update the label as scale or variable changes
-        self.__tracecb = self._variable.trace_variable('w', self._adjust)
+        self.__tracecb = self._variable.trace_add('write', self._adjust)
         self.bind('<Configure>', self._adjust)
         self.bind('<Map>', self._adjust)
 
@@ -1523,7 +1526,7 @@ def __init__(self, master=None, variable=None, from_=0, to=10, **kw):
     def destroy(self):
         """Destroy this widget and possibly its associated variable."""
         try:
-            self._variable.trace_vdelete('w', self.__tracecb)
+            self._variable.trace_remove('write', self.__tracecb)
         except AttributeError:
             pass
         else:

Misc/NEWS.d/next/Library/2024-06-07-13-21-11.gh-issue-120211.Rws_gf.rst

@@ -0,0 +1 @@
+Fix :mod:`tkinter.ttk` with Tcl/Tk 9.0.