Sometimes junk is left in the transaction when #returning

[asottile]

At the start of every Cheetah method, if there's no running transaction, Cheetah will create a dummy one and assign it to self.transaction. At the end of the method, if self.transaction is a dummy, Cheetah will set it back to None.

All is well and good, unless the method happens to use #return, in which case the cleanup code never runs. The cleanup should be in a finally block, instead.

Upshot of this problem:

#def foo():#return "hello"
#def bar():world

>>> tmpl.foo()
'hello'
>>> tmpl.bar()
<object object at 0x7f96764a40a0>

That anonymous object is actually the NO_CONTENT sentinel that Cheetah returns when it thinks it's being called within a transaction.

The fix is to clean up the transaction in a finally block.

[asottile]

Actually fixing this is a little more difficult than just slapping a try: finally: around this as there are other ways to exit the function.

For instance:

#def foo()
    #return 5
#end def

By putting the cleanup code in a finally block, you end up with compiled source which looks like this:

        trans = self.transaction
        if not trans:
            self.transaction = trans = DummyTransaction()
            _dummyTrans = True
        else:
            _dummyTrans = False
        write = trans.write
        SL = self._CHEETAH__searchList
        _filter = self._CHEETAH__currentFilter

        try:

            ## START - generated method body

            return 5

            ## END - generated method body

        finally:
            if _dummyTrans:
                self.transaction = None
                return trans.getvalue()
            else:
                return NO_CONTENT

Simplifying the problem from the above code:

def foo():
    x = ''
    try:
        return 5
    finally:
        return x

Will return ''

So somehow the finally block would both need to know whether or not the function has returned / excepted naturally and make a decision based on that. I assume some extra code would need to be added when #returning