diff -r edc8504bc26b -r 4cabeea6d214 hgext/hooklib/changeset_obsoleted.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext/hooklib/changeset_obsoleted.py	Sat Sep 07 14:50:39 2019 +0200
@@ -0,0 +1,131 @@
+# Copyright 2020 Joerg Sonnenberger <joerg@bec.de>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""changeset_obsoleted is a hook to send a mail when an
+existing draft changeset is obsoleted by an obsmarker without successor.
+
+Correct message threading requires the same messageidseed to be used for both
+the original notification and the new mail.
+
+Usage:
+  [notify]
+  messageidseed = myseed
+
+  [hooks]
+  pretxnclose.changeset_obsoleted = \
+    python:hgext.hooklib.changeset_obsoleted.hook
+"""
+
+from __future__ import absolute_import
+
+import email.errors as emailerrors
+import email.utils as emailutils
+
+from mercurial.i18n import _
+from mercurial import (
+    encoding,
+    error,
+    logcmdutil,
+    mail,
+    obsutil,
+    pycompat,
+    registrar,
+)
+from mercurial.utils import dateutil
+from .. import notify
+
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem(
+    b'notify_obsoleted', b'domain', default=None,
+)
+configitem(
+    b'notify_obsoleted', b'messageidseed', default=None,
+)
+configitem(
+    b'notify_obsoleted',
+    b'template',
+    default=b'''Subject: changeset abandoned
+
+This changeset has been abandoned.
+''',
+)
+
+
+def _report_commit(ui, repo, ctx):
+    domain = ui.config(b'notify_obsoleted', b'domain') or ui.config(
+        b'notify', b'domain'
+    )
+    messageidseed = ui.config(
+        b'notify_obsoleted', b'messageidseed'
+    ) or ui.config(b'notify', b'messageidseed')
+    template = ui.config(b'notify_obsoleted', b'template')
+    spec = logcmdutil.templatespec(template, None)
+    templater = logcmdutil.changesettemplater(ui, repo, spec)
+    ui.pushbuffer()
+    n = notify.notifier(ui, repo, b'incoming')
+
+    subs = set()
+    for sub, spec in n.subs:
+        if spec is None:
+            subs.add(sub)
+            continue
+        revs = repo.revs(b'%r and %d:', spec, ctx.rev())
+        if len(revs):
+            subs.add(sub)
+            continue
+    if len(subs) == 0:
+        ui.debug(
+            b'notify_obsoleted: no subscribers to selected repo and revset\n'
+        )
+        return
+
+    templater.show(
+        ctx,
+        changes=ctx.changeset(),
+        baseurl=ui.config(b'web', b'baseurl'),
+        root=repo.root,
+        webroot=n.root,
+    )
+    data = ui.popbuffer()
+
+    try:
+        msg = mail.parsebytes(data)
+    except emailerrors.MessageParseError as inst:
+        raise error.Abort(inst)
+
+    msg['In-reply-to'] = notify.messageid(ctx, domain, messageidseed)
+    msg['Message-Id'] = notify.messageid(
+        ctx, domain, messageidseed + b'-obsoleted'
+    )
+    msg['Date'] = encoding.strfromlocal(
+        dateutil.datestr(format=b"%a, %d %b %Y %H:%M:%S %1%2")
+    )
+    if not msg['From']:
+        sender = ui.config(b'email', b'from') or ui.username()
+        if b'@' not in sender or b'@localhost' in sender:
+            sender = n.fixmail(sender)
+        msg['From'] = mail.addressencode(ui, sender, n.charsets, n.test)
+    msg['To'] = ', '.join(sorted(subs))
+
+    msgtext = msg.as_bytes() if pycompat.ispy3 else msg.as_string()
+    if ui.configbool(b'notify', b'test'):
+        ui.write(msgtext)
+        if not msgtext.endswith(b'\n'):
+            ui.write(b'\n')
+    else:
+        ui.status(_(b'notify_obsoleted: sending mail for %d\n') % ctx.rev())
+        mail.sendmail(
+            ui, emailutils.parseaddr(msg['From'])[1], subs, msgtext, mbox=n.mbox
+        )
+
+
+def hook(ui, repo, hooktype, node=None, **kwargs):
+    if hooktype != b"pretxnclose":
+        raise error.Abort(
+            _(b'Unsupported hook type %r') % pycompat.bytestr(hooktype)
+        )
+    for rev in obsutil.getobsoleted(repo, repo.currenttransaction()):
+        _report_commit(ui, repo, repo.unfiltered()[rev])