[Zope-dev] Re: Zope 2.8: ZODB fix breaks undoable_transactions

[yuppie]

Tim Peters wrote:
> [yuppie]
> 
>>...
>>Don't know what other people think. I believe restoring the old undoInfo
>>behavior and adjusting the documentation would be the best solution.
>>Fixing this in undoable_transactions would fork the behavior of both
>>methods and fixing all products that depend on the old behavior would
>>cause unnecessary trouble.
> 
> 
> Can you document the behavior you want?  Because there were multiple
> bugs in the implementation before, I'm not exactly sure what "old
> behavior" was in all cases; I'm certain that _some_ of it was purely
> accidental, never intended, and utterly surprising (when last < 0). 
> ZODB/interfaces.py's IStorageUndoable.undoLog documents the current
> behavior, which matches what ZODB's UML docs have always claimed
> behavior should be.  This behavior is tested in ZODB too now, so any
> change here requires fiddling code, docs and tests.  If Zope requires
> particular behaviors, it should grow tests for those too.
> 
> I'd be happy enough changing `first` and `last` to act like Python
> slice indices instead, with the caveat that because there's other
> weird non-Python behavior mandated when last < 0 (then undo{Log,Info}
> are documented as taking the absolute value of `last` as being an
> upper bound on the # of results to return -- and "old behavior" was
> related to that, albeit with bugs of its own), they cannot act like
> Python slice indices unless `first` and `last` are both non-negative.

Zope 2 uses 'undoInfo' only in one place: 'undoable_transactions'. And 
'undoable_transactions' is only used for the undo tab.

CMF uses 'undoable_transactions' in a similar way than Zope 2. The 
problem with the CMF code is that it should work in a consistent way 
with Zope 2.7 and 2.8.

These are the two use cases I'm aware of. Both only use last > 0 and 
both expect slicing behavior for positive values, e.g. these conditions 
should be True if we don't change undoable_transactions::

   db.undoInfo(0, 20) == db.undoInfo(0, 99)[0:20]
   db.undoInfo(20, 40) == db.undoInfo(0, 99)[20:40]

I don't care very much *how* this is resolved. All I want is to get the 
regressions in Zope 2 and CMF fixed.

Cheers, Yuppie