[PATCH 2 of 4] revset: add __length_hint__ to smart classes

[Durham Goode]

On 9/29/14, 6:47 PM, Durham Goode wrote:
>
> On 9/29/14, 6:12 PM, Durham Goode wrote:
>> # HG changeset patch
>> # User Durham Goode <durham at fb.com>
>> # Date 1412036731 25200
>> #      Mon Sep 29 17:25:31 2014 -0700
>> # Node ID 93be919300f04bfd26fd5294499fb62c96ba7f93
>> # Parent  c6129c781a9f11be26191e64dcebf8d539c8c76a
>> revset: add __length_hint__ to smart classes
>>
>> This adds a __length_hint__ to the smart revset classes so we can 
>> optimize at
>> runtime to avoid things like iterating over the large set and checking
>> containment against the small set when doing 'X & Y'.
>>
>> diff --git a/mercurial/revset.py b/mercurial/revset.py
>> --- a/mercurial/revset.py
>> +++ b/mercurial/revset.py
>> @@ -2204,6 +2204,9 @@ class baseset(list):
>>           super(baseset, self).__init__(data)
>>           self._set = None
>>   +    def __length_hint__(self):
>> +        return len(self)
>> +
>>       def ascending(self):
>>           """Sorts the set in ascending order (in place).
>>   @@ -2376,6 +2379,9 @@ class lazyset(object):
>>           l = baseset([r for r in self])
>>           return len(l)
>>   +    def __length_hint__(self):
>> +        return self._subset.__length_hint__()
>> +
> I'm not 100% satisfied with this stuff.  _subset is not guaranteed to 
> be a smart set, and therefore might not even implement 
> __length_hint__.  But to fix it would require auditing every revset to 
> ensure that subsets are always one of our smartsets.
I've sent a V2 that addresses this issue.