[PATCH 1 of 3] revert: add a fullreposet class

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1398823575 25200
#      Tue Apr 29 19:06:15 2014 -0700
# Node ID 9daf8851618b46b112314848bd639dadf6ca7381
# Parent  273bf648227540a7ef87c4794e96b8a9d915d5b7
revert: add a fullreposet class

Every revset evaluation starts from `subset = spanset(repo)` and a lot of
revset predicates build a `spansetrepo` for their internal needs.

`spanset` is a generic class that can handle any situation. As a result a lot
of operation between spanset result in an `orderedlazyset`, a safe object but
suboptimal in may situation.

So we introduce a `fullreposet` class where some of the operation will be
overwritten to produce more interesting results.

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2845,7 +2845,16 @@ class spanset(_orderedsetmixin):
         return self._start >= self._end
 
     def filter(self, l):
         return orderedlazyset(self, l, ascending=self.isascending())
 
+class fullreposet(spanset):
+    """a set containing all revisions in the repo
+
+    This class exists to host special optimisation.
+    """
+
+    def __init__(self, repo):
+        super(fullreposet, self).__init__(repo)
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = symbols.values()