rebase: improve error message for empty --source set Before, it just said 'nothing to rebase' in this case. Now, it aborts mentioning the reason: 'empty "source" revision set'. Specifying revisions that cannot be rebased is a 'soft' error, but specifying an empty set deserves an abort that explains exactly what the problem is.

--- a/tests/test-rebase-parameters.t
+++ b/tests/test-rebase-parameters.t
@@ -83,6 +83,10 @@
   abort: empty "rev" revision set - nothing to rebase
   [255]
 
+  $ hg rebase --source '1 & !1'
+  abort: empty "source" revision set - nothing to rebase
+  [255]
+
   $ hg rebase
   nothing to rebase
   [1]