shortest: move revnum-disambiguation out of revlog

I want to be able to change how we disambiguate and I think having
revlog.shortest() worry only about finding a prefix that's unambiguous
among nodeids makes more sense.

This slows down `hg log -T '{shortest(node,1)}\n'` from 4.0s to 4.1s.

Differential Revision: https://phab.mercurial-scm.org/D3502

mercurial/revlog.py

@@ -1502,18 +1502,6 b' class revlog(object):'
 
     def shortest(self, node, minlength=1):
         """Find the shortest unambiguous prefix that matches node."""
-        def isrev(prefix):
-            try:
-                i = int(prefix)
-                # if we are a pure int, then starting with zero will not be
-                # confused as a rev; or, obviously, if the int is larger
-                # than the value of the tip rev
-                if prefix[0] == '0' or i > len(self):
-                    return False
-                return True
-            except ValueError:
-                return False
-
         def isvalid(prefix):
             try:
                 node = self._partialmatch(prefix)
@@ -1532,9 +1520,10 b' class revlog(object):'
         hexnode = hex(node)
 
         def disambiguate(hexnode, minlength):
+            """Disambiguate against wdirid."""
             for length in range(minlength, 41):
                 prefix = hexnode[:length]
-                if not isrev(prefix) and not maybewdir(prefix):
+                if not maybewdir(prefix):
                     return prefix
 
         if not getattr(self, 'filteredrevs', None):

mercurial/scmutil.py

@@ -449,8 +449,30 b' def shortesthexnodeidprefix(repo, node, '
     # _partialmatch() of filtered changelog could take O(len(repo)) time,
     # which would be unacceptably slow. so we look for hash collision in
     # unfiltered space, which means some hashes may be slightly longer.
+    cl = repo.unfiltered().changelog
+
+    def isrev(prefix):
+        try:
+            i = int(prefix)
+            # if we are a pure int, then starting with zero will not be
+            # confused as a rev; or, obviously, if the int is larger
+            # than the value of the tip rev
+            if prefix[0] == '0' or i > len(cl):
+                return False
+            return True
+        except ValueError:
+            return False
+
+    def disambiguate(prefix):
+        """Disambiguate against revnums."""
+        hexnode = hex(node)
+        for length in range(len(prefix), 41):
+            prefix = hexnode[:length]
+            if not isrev(prefix):
+                return prefix
+
     try:
-        return repo.unfiltered().changelog.shortest(node, minlength)
+        return disambiguate(cl.shortest(node, minlength))
     except error.LookupError:
         raise error.RepoLookupError()