# HG changeset patch
# User Augie Fackler <augie@google.com>
# Date 2018-09-20 13:52:59
# Node ID 5adc5fe41a7daa292272f43493a23e4aa7a3d9b6
# Parent  e03c1a63155cb6443f9b5da592ef40a1b17208f8

changegroup: reintroduce some comments that have gotten lost over the years

I got concerned about the correctness of the pruning logic, but I was
misreading it. I didn't figure that out until I walked all the way
back to 0252abaafb8a from 20111, where I was finally able to see (in
the deleted side of the change!) a complete explanation from
b6d9ea0bc107 in 2005.

Differential Revision: https://phab.mercurial-scm.org/D4686

diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -1071,8 +1071,14 @@ class cgpacker(object):
             store = mfl.getstorage(tree)
 
             if not self._filematcher.visitdir(store.tree[:-1] or '.'):
+                # No nodes to send because this directory is out of
+                # the client's view of the repository (probably
+                # because of narrow clones).
                 prunednodes = []
             else:
+                # Avoid sending any manifest nodes we can prove the
+                # client already has by checking linkrevs. See the
+                # related comment in generatefiles().
                 prunednodes = self._prunemanifests(store, nodes, commonrevs)
             if tree and not prunednodes:
                 continue
@@ -1164,6 +1170,10 @@ class cgpacker(object):
                 return linkrevnodes[x]
 
             frev, flr = filerevlog.rev, filerevlog.linkrev
+            # Skip sending any filenode we know the client already
+            # has. This avoids over-sending files relatively
+            # inexpensively, so it's not a problem if we under-filter
+            # here.
             filenodes = [n for n in linkrevnodes
                          if flr(frev(n)) not in commonrevs]