revset: extend fullreposet to make "null" revision magically appears in set

As per fullreposet.__and__, it can omit the range check of rev.  Therefore,
"null" revision is accepted automagically.

It seems this can fix many query results involving null symbol.  Originally,
the simplest "(null)" query did fail if there were hidden revisions.  Tests
are randomly chosen.

fullreposet mimics the behavior of localrepo, where "null" revision is not
listed but contained.

mercurial/revset.py

@@ -323,8 +323,6 b' def _getrevsource(repo, r):'
 
 def stringset(repo, subset, x):
     x = repo[x].rev()
-    if x == -1 and len(subset) == len(repo):
-        return baseset([-1])
     if x in subset:
         return baseset([x])
     return baseset()
@@ -3312,16 +3310,17 b' class spanset(abstractsmartset):'
 class fullreposet(spanset):
     """a set containing all revisions in the repo
 
-    This class exists to host special optimization.
+    This class exists to host special optimization and magic to handle virtual
+    revisions such as "null".
     """
 
     def __init__(self, repo):
         super(fullreposet, self).__init__(repo)
 
     def __contains__(self, rev):
+        # assumes the given rev is valid
         hidden = self._hiddenrevs
-        return ((self._start <= rev < self._end)
-                and not (hidden and rev in hidden))
+        return not (hidden and rev in hidden)
 
     def __and__(self, other):
         """As self contains the whole repo, all of the other set should also be

tests/test-obsolete.t

@@ -187,6 +187,8 b' check that various commands work well wi'
   [255]
   $ hg debugrevspec 'rev(6)'
   $ hg debugrevspec 'rev(4)'
+  $ hg debugrevspec 'null'
+  -1
 
 Check that public changeset are not accounted as obsolete:
 

tests/test-revset.t

@@ -478,8 +478,33 b' Test explicit numeric revision'
   [255]
 
 Test null revision
+  $ log '(null)'
+  -1
+  $ log '(null:0)'
+  -1
+  0
+  $ log '(0:null)'
+  0
+  -1
+  $ log 'null::0'
+  -1
+  0
+  $ log 'null:tip - 0:'
+  -1
+  $ log 'null: and null::' | head -1
+  -1
+  $ log 'null: or 0:' | head -2
+  -1
+  0
   $ log 'ancestors(null)'
   -1
+  $ log 'reverse(null:)' | tail -2
+  0
+  -1
+  $ log 'first(null:)'
+  -1
+  $ log 'min(null:)'
+  -1
   $ log 'tip:null and all()' | tail -2
   1
   0