obsstore: add a flag for sha256 hashes

We add flag to inform that the marker is using sha256 hashes. As format 0 is not
able to handle sha256 hashes (32 bytes long), we plain crash if we even attempt to
encode a sha256 with it.

mercurial/obsolete.py

@@ -112,6 +112,7 b' from i18n import _'
 # bumped version and fix the situation, breaking the transitivity of
 # "bumped" here.
 bumpedfix = 1
+usingsha256 = 2
 
 ## Parsing and writing of version "0"
 #
@@ -193,6 +194,8 b' def _fm0readmarkers(data, off=0):'
 
 def _fm0encodeonemarker(marker):
     pre, sucs, flags, metadata, date, parents = marker
+    if flags & usingsha256:
+        raise util.Abort(_('cannot handle sha256 with old obsstore format'))
     metadata = dict(metadata)
     metadata['date'] = '%d %i' % date
     if parents is not None: