revset: added isascending and isdescending methods to smartset classes

This methods state if the class is sorted in an ascending or descending order

We need this to implement methods based on order on smartset classes in order
to be able to create new objects with a given order.

We cannot just rely on a simple boolean since unordered set are neither
ascending nor descending.

mercurial/revset.py

@@ -2204,6 +2204,12 b' class baseset(list):'
         l = [r for r in x if r not in s]
         return baseset(list(self) + l)
 
+    def isascending(self):
+        return False
+
+    def isdescending(self):
+        return False
+
     def filter(self, l):
         return lazyset(self, l)
 
@@ -2270,6 +2276,12 b' class lazyset(object):'
     def set(self):
         return set([r for r in self])
 
+    def isascending(self):
+        return False
+
+    def isdescending(self):
+        return False
+
     def filter(self, l):
         return lazyset(self, l)
 
@@ -2309,6 +2321,12 b' class orderedlazyset(lazyset):'
                 self._subset.sort(reverse=reverse)
         self._ascending = not reverse
 
+    def isascending(self):
+        return self._ascending
+
+    def isdescending(self):
+        return not self._ascending
+
     def reverse(self):
         self._subset.reverse()
         self._ascending = not self._ascending
@@ -2621,6 +2639,12 b' class spanset(object):'
     def set(self):
         return self
 
+    def isascending(self):
+        return self._start < self._end
+
+    def isdescending(self):
+        return self._start > self._end
+
     def filter(self, l):
         if self._start <= self._end:
             return orderedlazyset(self, l)