smartset: split generatorset classes to avoid cycle...
smartset: split generatorset classes to avoid cycle
I uncovered a cycle manifesting in a memory leak by running
`hgperfrevset '::tip'`. The cycle was due to generatorset.__init__
assigning a bound method to self.__contains__. Internet sleuthing
revealed that assigning a bound method to an instance attribute
always creates a cycle.
This commit creates two new variants of generatorset for the special
cases of ascending and descending generators. The special
implementations of __contains__ have been extracted to these classes
where they are defined as __contains__.
generatorset now implements __new__ and changes the spawned type to
one of the new classes if needed.
Differential Revision:
https://phab.mercurial-scm.org/D1780
