[MixMaster] Fix crash when using Tcl 8.6

Tcl/Tk changed some operations which previously resulted in undefined behavior
into errors, including one case that occurred when updating the "Mixtures" menu
in MixMaster.

MixMaster now modifies the existing Menu when adding an item, rather than
completely regenerating it, which avoids this problem.

Fixes Issue 235.

interfaces/cython/cantera/mixmaster/ControlPanel.py

@@ -106,40 +106,35 @@ def make_menu(name, menubar, lst):
     button=Menubutton(menubar, text=name, width=nc+4, padx=3,pady=1)
     button.pack(side=LEFT)
     menu = Menu(button,tearoff=FALSE)
-    m = menu
-    i = 0
     for entry in lst:
-        i += 1
-        if entry == 'separator':
-            menu.add_separator({})
-        elif isinstance(entry, list):
-            for num in entry:
-                menu.entryconfig(num,state=DISABLED)
-        elif not isinstance(entry[1], list):
-            if i == 20:
-                i = 0
-                submenu = Menu(button,tearoff=FALSE)
-                m.add_cascade(label='More...',
-                                 menu=submenu)
-                m = submenu
-            if len(entry) == 2 or entry[2] == 'command':
-                m.add_command(label=entry[0],
-                              command=entry[1])
-            elif entry[2] == 'check':
-                entry[3].set(0)
-                if len(entry) >= 5: val = entry[4]
-                else: val = 1
-                m.add_checkbutton(label=entry[0],
-                                     command=entry[1],
-                                     variable = entry[3],
-                                     onvalue=val)
-        else:
-            submenu=make_menu(entry[0], menu, entry[1])
-            m.add_cascade(label=entry[0],
-                             menu=submenu)
+        add_menu_item(menu, entry)
     button['menu']=menu
     return button
 
+def add_menu_item(menu, entry):
+    if entry == 'separator':
+        menu.add_separator({})
+    elif isinstance(entry, list):
+        for num in entry:
+            menu.entryconfig(num,state=DISABLED)
+    elif not isinstance(entry[1], list):
+        if len(entry) == 2 or entry[2] == 'command':
+            menu.add_command(label=entry[0],
+                             command=entry[1])
+        elif entry[2] == 'check':
+            entry[3].set(0)
+            if len(entry) >= 5: val = entry[4]
+            else: val = 1
+            menu.add_checkbutton(label=entry[0],
+                                 command=entry[1],
+                                 variable = entry[3],
+                                 onvalue=val)
+    else:
+        submenu=make_menu(entry[0], menu, entry[1])
+        menu.add_cascade(label=entry[0],
+                         menu=submenu)
+
+
 def menuitem_state(button, *statelist):
     for menu in button.children.keys():
         if isinstance(button.children[menu], Menu):

interfaces/cython/cantera/mixmaster/MechManager.py

@@ -7,7 +7,7 @@ else:
     from Tkinter import *
 
 from .ControlPanel import ControlWindow
-from .ControlPanel import make_menu, menuitem_state
+from .ControlPanel import make_menu, menuitem_state, add_menu_item
 #from Cantera.Examples.Tk import _mechdir
 import os
 
@@ -52,9 +52,9 @@ class MechManager(Frame):
         self.mechanisms.append((name, mech))
         il = len(self.mechanisms)
         self.mlist[-1] = (name, self.setMechanism, 'check', self.mechindx, il)
+        add_menu_item(list(self.mechmenu.children.values())[0], self.mlist[-1])
         self.mlist.append([])
 
-        self.mechmenu = make_menu('Mixtures', self, self.mlist)
         self.mechindx.set(il)
         self.mechmenu.grid(row=0,column=0,sticky=W)