[PATCH 5 of 5 EVOLVE] fold: improve error messages for multiple heads and roots

[Jordi Gutiérrez Hermoso]

# HG changeset patch
# User Jordi Gutiérrez Hermoso <jordigh at octave.org>
# Date 1404149929 14400
#      Mon Jun 30 13:38:49 2014 -0400
# Node ID a8b505057e4e4bac8ffa54bd0f89ef7eaa03edc6
# Parent  410a9c3b3232bbb0fd6cd4427b0174311c3ce803
fold: improve error messages for multiple heads and roots

This commit adds hints and i18n to the error messages about non-linear
revisions, along with corresponding tests.

diff --git a/hgext/evolve.py b/hgext/evolve.py
--- a/hgext/evolve.py
+++ b/hgext/evolve.py
@@ -2116,13 +2116,15 @@ def fold(ui, repo, *revs, **opts):
 
     roots = repo.revs('roots(%ld)', revs)
     if len(roots) > 1:
-        raise util.Abort("set has multiple roots")
+        raise util.Abort(_("cannot fold non-linear revisions"),
+                           hint=_("multiple roots detected"))
     root = repo[roots[0]]
     if root.phase() <= phases.public:
         raise util.Abort(_("cannot fold public revisions"))
     heads = repo.revs('heads(%ld)', revs)
     if len(heads) > 1:
-        raise util.Abort("set has multiple heads")
+        raise util.Abort(_("cannot fold non-linear revisions"),
+                           hint=_("multiple heads detected"))
     head = repo[heads[0]]
     wlock = lock = None
     try:
diff --git a/tests/test-evolve.t b/tests/test-evolve.t
--- a/tests/test-evolve.t
+++ b/tests/test-evolve.t
@@ -619,6 +619,14 @@ Test fold
   $ hg fold .
   single revision specified, nothing to fold
   [1]
+  $ hg fold 0::10 --rev 1 --exact
+  abort: cannot fold non-linear revisions
+  (multiple heads detected)
+  [255]
+  $ hg fold -r 4 -r 6 --exact
+  abort: cannot fold non-linear revisions
+  (multiple roots detected)
+  [255]
   $ hg fold 10 1
   abort: cannot fold non-linear revisions
   (given revisions are unrelated to parent of working directory)