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

[Durham Goode]

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.