# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@octobus.net>
# Date 2019-03-07 00:28:24
# Node ID 3ba9ca537f57ecd37ff6f72926d0d8824dc5b0a8
# Parent  6a944bf4c43ad2174f021d790ada9770668188b7

discovery: clarify why the caching of children is valid

Yuya Nishihara pointed out that the code looks wrong without this clarification.
(And, unsurprisingly, Yuya is right)

diff --git a/mercurial/setdiscovery.py b/mercurial/setdiscovery.py
--- a/mercurial/setdiscovery.py
+++ b/mercurial/setdiscovery.py
@@ -175,6 +175,10 @@ class partialdiscovery(object):
     def _childrengetter(self):
 
         if self._childrenmap is not None:
+            # During discovery, the `undecided` set keep shrinking.
+            # Therefore, the map computed for an iteration N will be
+            # valid for iteration N+1. Instead of computing the same
+            # data over and over we cached it the first time.
             return self._childrenmap.__getitem__
 
         # _updatesample() essentially does interaction over revisions to look