insults ContainerWidget doesn't remove focus when child removed

[magmatt]

If a ContainerWidget's focusedChild is removed, focus is not removed.

This is bad because the focusedChild continues to receive characterReceived calls instead of newly added children.

Here's some code that demonstrates the problem:

>>> from twisted.conch.insults.window import Widget, ContainerWidget
>>> c = ContainerWidget()
>>> c.focused = True
>>> a = Widget()
>>> c.addChild(a)
>>> assert c.focusedChild == a
>>> c.remChild(a)
>>> assert c.focusedChild == None
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError
>>> c.focusedChild == a
True

[magmatt]

Patch attempt

[magmatt]

I changed the test code to this to avoid Container throwing YieldFocus:

from twisted.conch.insults.window import Widget, TopWindow
c = TopWindow(lambda: None, lambda x:None)                
c.focusReceived()                                         
a = Widget()                                              
c.addChild(a)                                             
assert c.focusedChild == a, (c.focusedChild, a)           
c.remChild(a)                                             
assert c.focusedChild == None, c.focusedChild             
assert a not in c.children, 'should remove'               

and here's the patch:

window.py

@@ -139 +139 @@
         assert child.parent is self              
         child.parent = None                      
         self.children.remove(child)              
+        if self.focusedChild == child:           
+            self.changeFocus()                   
         self.repaint()                           
                                                  
     def filthy(self):                            

[magmatt]

Hmm... it would also work if changeFocus were run after the repaint. I think this might be better. Someone who knows more about how things work together could judge:

window.py

@@ -140 +140 @@
         child.parent = None                      
         self.children.remove(child)              
         self.repaint()                           
+        if self.focusedChild == child:           
+            self.changeFocus()                   
                                                  
     def filthy(self):                            
         for ch in self.children: