smartset: fix generatorset.last() to not return the first element (issue5609)

mercurial/smartset.py

@@ -766,6 +766,11 b' class generatorset(abstractsmartset):'
     be iterated more than once.
     When asked for membership it generates values until either it finds the
     requested one or has gone through all the elements in the generator
+
+    >>> xs = generatorset([0, 1, 4], iterasc=True)
+    >>> assert xs.last() == xs.last()
+    >>> xs.last()  # cached
+    4
     """
     def __init__(self, gen, iterasc=None):
         """
@@ -937,7 +942,7 b' class generatorset(abstractsmartset):'
             # we need to consume all and try again
             for x in self._consumegen():
                 pass
-            return self.first()
+            return self.last()
         return next(it(), None)
 
     def __repr__(self):

tests/test-revset.t

@@ -1337,6 +1337,16 b' Test order of first/last revisions'
   0
   1
 
+Test scmutil.revsingle() should return the last revision
+
+  $ hg debugrevspec -s 'last(0::)'
+  * set:
+  <baseset slice=0:1
+    <generatorset->>
+  9
+  $ hg identify -r '0::' --num
+  9
+
 Test matching
 
   $ log 'matching(6)'