diff hgext/notify.py @ 44631:947e6df4ff77

notify: optional mail threading based on obsmarker

When notify.reply is set and a changeset has a predecessor in the
repository, include In-Reply-To pointing to the message-id that would
have been generated for the oldest predecessor. This allows mail
threading like Phabricator for common cases like rebasing changes, but
will be optimal for cases like folding.

Differential Revision: https://phab.mercurial-scm.org/D8172

--- a/hgext/notify.py	Fri Mar 27 10:39:59 2020 -0400
+++ b/hgext/notify.py	Wed Feb 26 22:35:39 2020 +0100
@@ -133,6 +133,15 @@
   the "From" field of the notification mail. If not set, take the user
   from the pushing repo.  Default: False.
 
+notify.reply-to-predecessor (EXPERIMENTAL)
+  If set and the changeset has a predecessor in the repository, try to thread
+  the notification mail with the predecessor. This adds the "In-Reply-To" header
+  to the notification mail with a reference to the predecessor with the smallest
+  revision number. Mail threads can still be torn, especially when changesets
+  are folded.
+
+  This option must  be used in combination with ``notify.messageidseed``.
+
 If set, the following entries will also be used to customize the
 notifications:
 
@@ -160,6 +169,7 @@
     error,
     logcmdutil,
     mail,
+    obsutil,
     patch,
     pycompat,
     registrar,
@@ -219,6 +229,9 @@
     b'notify', b'outgoing', default=None,
 )
 configitem(
+    b'notify', b'reply-to-predecessor', default=False,
+)
+configitem(
     b'notify', b'sources', default=b'serve',
 )
 configitem(
@@ -281,6 +294,16 @@
         self.merge = self.ui.configbool(b'notify', b'merge')
         self.showfunc = self.ui.configbool(b'notify', b'showfunc')
         self.messageidseed = self.ui.config(b'notify', b'messageidseed')
+        self.reply = self.ui.configbool(b'notify', b'reply-to-predecessor')
+
+        if self.reply and not self.messageidseed:
+            raise error.Abort(
+                _(
+                    b'notify.reply-to-predecessor used without '
+                    b'notify.messageidseed'
+                )
+            )
+
         if self.showfunc is None:
             self.showfunc = self.ui.configbool(b'diff', b'showfunc')
 
@@ -437,6 +460,26 @@
         msg['X-Hg-Notification'] = 'changeset %s' % ctx
         if not msg['Message-Id']:
             msg['Message-Id'] = messageid(ctx, self.domain, self.messageidseed)
+        if self.reply:
+            unfi = self.repo.unfiltered()
+            has_node = unfi.changelog.index.has_node
+            predecessors = [
+                unfi[ctx2]
+                for ctx2 in obsutil.allpredecessors(unfi.obsstore, [ctx.node()])
+                if ctx2 != ctx.node() and has_node(ctx2)
+            ]
+            if predecessors:
+                # There is at least one predecessor, so which to pick?
+                # Ideally, there is a unique root because changesets have
+                # been evolved/rebased one step at a time. In this case,
+                # just picking the oldest known changeset provides a stable
+                # base. It doesn't help when changesets are folded. Any
+                # better solution would require storing more information
+                # in the repository.
+                pred = min(predecessors, key=lambda ctx: ctx.rev())
+                msg['In-Reply-To'] = messageid(
+                    pred, self.domain, self.messageidseed
+                )
         msg['To'] = ', '.join(sorted(subs))
 
         msgtext = msg.as_bytes() if pycompat.ispy3 else msg.as_string()