bpo-23544: IDLE hangs when selecting Stack Viewer with debug active

"Stack Viewer" is now disabled when user code is running.

Lib/idlelib/editor.py

@@ -449,7 +449,9 @@ class EditorWindow(object):
         self.menudict = menudict = {}
         for name, label in self.menu_specs:
             underline, label = prepstr(label)
-            menudict[name] = menu = Menu(mbar, name=name, tearoff=0)
+            postcommand = getattr(self, f'{name}_menu_postcommand', None)
+            menudict[name] = menu = Menu(mbar, name=name, tearoff=0,
+                                         postcommand=postcommand)
             mbar.add_cascade(label=label, menu=menu, underline=underline)
         if macosx.isCarbonTk():
             # Insert the application menu

Lib/idlelib/pyshell.py

@@ -990,6 +990,10 @@ class PyShell(OutputWindow):
         self.showprompt()
         self.set_debugger_indicator()
 
+    def debug_menu_postcommand(self):
+        state = 'disabled' if self.executing else 'normal'
+        self.update_menu_state('debug', '*Stack Viewer', state)
+
     def beginexecuting(self):
         "Helper for ModifiedInterpreter"
         self.resetoutput()

Misc/NEWS.d/next/IDLE/2019-11-14-23-41-07.bpo-23544.3etemb.rst

@@ -0,0 +1,2 @@
+The "Stack Viewer" item in the "Debug" menu can no longer be selected when
+user code is running.