[PATCH 1 of 4] revset: fix crash on empty sort key

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1465990644 -32400
#      Wed Jun 15 20:37:24 2016 +0900
# Node ID 05e51f240485ea6a8490342deda2ce1f08c33bbf
# Parent  8bf84295e59ba0c98e64fd7ccf3f809e4da5b237
revset: fix crash on empty sort key

Make it noop as before 2188f170f5b6. We could change it to an error, but
allowing empty key makes some sense for scripting that builds a key string
programmatically.

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1890,6 +1890,8 @@ def sort(repo, subset, x):
                 'topo.firstbranch can only be used when using the topo sort '
                 'key'))
 
+    if not keys:
+        return revs
     if keys == ["rev"]:
         revs.sort()
         return revs
diff --git a/tests/test-revset.t b/tests/test-revset.t
--- a/tests/test-revset.t
+++ b/tests/test-revset.t
@@ -962,6 +962,13 @@ test sorting two sorted collections in d
   6
   2
 
+test empty sort key which is noop
+
+  $ log 'sort(0 + 2 + 1, "")'
+  0
+  2
+  1
+
 test invalid sort keys
 
   $ log 'sort(all(), -invalid)'