obsolete: add a high level function to create an obsolete marker

This function is designed to be used by all code that creates new
obsolete markers in the local repository.

It is not used by debugobsolete because debugobsolete allows the
use of an unknown hash as argument.

mercurial/obsolete.py

@@ -395,3 +395,39 b' def _computesuspendedset(repo):'
 def _computeextinctset(repo):
     """the set of obsolete parents without non obsolete descendants"""
     return set(repo.revs('obsolete() - obsolete()::unstable()'))
+
+def createmarkers(repo, relations, flag=0, metadata=None):
+    """Add obsolete markers between changesets in a repo
+
+    <relations> must be an iterable of (<old>, (<new>, ...)) tuple.
+    `old` and `news` are changectx.
+
+    Trying to obsolete a public changeset will raise an exception.
+
+    Current user and date are used except if specified otherwise in the
+    metadata attribute.
+
+    This function operates within a transaction of its own, but does
+    not take any lock on the repo.
+    """
+    # prepare metadata
+    if metadata is None:
+        metadata = {}
+    if 'date' not in metadata:
+        metadata['date'] = '%i %i' % util.makedate()
+    if 'user' not in metadata:
+        metadata['user'] = repo.ui.username()
+    tr = repo.transaction('add-obsolescence-marker')
+    try:
+        for prec, sucs in relations:
+            if not prec.mutable():
+                raise util.Abort("cannot obsolete immutable changeset: %s"
+                                 % prec)
+            nprec = prec.node()
+            nsucs = tuple(s.node() for s in sucs)
+            if nprec in nsucs:
+                raise util.Abort("changeset %s cannot obsolete itself" % prec)
+            repo.obsstore.create(tr, nprec, nsucs, flag, metadata)
+        tr.close()
+    finally:
+        tr.release()