The reply indicator for individual messages was always empty, and the
reply indicator for the cover letter showed comments for the entire
series.  (This happened to be correct for the two cases I used for
testing...).  Use an EXISTS subquery just like the series view does
to fix it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
	I've applied this patch.

 mods/diff.py | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/mods/diff.py b/mods/diff.py
index d1b30af..eb8dfb8 100644
--- a/mods/diff.py
+++ b/mods/diff.py
@@ -17,6 +17,7 @@ from django.http import Http404
 from django.urls import reverse
 from django.utils.html import format_html
 from django.utils.safestring import mark_safe
+from django.db.models import Exists, OuterRef
 from mod import PatchewModule
 from api.models import Project, Message
 from api.rest import PluginMethodField
@@ -76,7 +77,7 @@ class DiffModule(PatchewModule):
             html = html + format_html(' <a href="{}">v{}</a>', url, v)
         message.extra_links.append({"html": mark_safe(html), "icon": "exchange" })
 
-    def _get_series_for_diff(self, s):
+    def _get_series_for_diff(self, q):
         def _get_message_data(m):
             filtered = ""
             sep = ""
@@ -92,21 +93,28 @@ class DiffModule(PatchewModule):
             return PatchInfo(
                 subject=m.subject,
                 link=m.get_message_view_url(),
-                has_replies=m.last_comment_date is not None,
+                has_replies=m.has_replies,
                 body=filtered)
 
+        def _add_has_replies(q, **kwargs):
+            replies = Message.objects.filter(in_reply_to=OuterRef('message_id'), **kwargs)
+            return q.annotate(has_replies=Exists(replies))
+
+        q = _add_has_replies(q, is_patch=False)
+        s = q.first()
+
         ret = list()
+        data = _get_message_data(s)
+        ret.append(data)
         if not s.is_patch:
-            data = _get_message_data(s)
-            ret.append(data)
-        for p in s.get_patches():
-            data = _get_message_data(p)
-            ret.append(data)
+            for p in _add_has_replies(s.get_patches()):
+                data = _get_message_data(p)
+                ret.append(data)
         return ret
 
     def www_view_series_diff(self, request, project, series_left, series_right):
-        sl = Message.objects.filter(project__name=project, message_id=series_left).first()
-        sr = Message.objects.filter(project__name=project, message_id=series_right).first()
+        sl = Message.objects.filter(project__name=project, message_id=series_left)
+        sr = Message.objects.filter(project__name=project, message_id=series_right)
         return render_page(request, "series-diff.html",
                            series_left=self._get_series_for_diff(sl),
                            series_right=self._get_series_for_diff(sr))
-- 
2.14.3