dgit: Write down quilt mode split brain plans in a comment

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/dgit b/dgit
index fbf5183eabb8f10c22cb1fb4103fe04a69097f0e..109092bee36d39a7f257caa2d7144aa5430d6a3c 100755 (executable)
--- a/dgit
+++ b/dgit
@@ -178,6 +178,29 @@ our $supplementary_message = '';
 our $split_brain = 0;
 our $do_split_brain = 0;
 
+# Interactions between quilt mode and split brain
+# (currently, split brain only implemented iff
+#  madformat_wantfixup && quiltmode_splitbrain)
+#
+#   source format        sane           `3.0 (quilt)'
+#                                       madformat_wantfixup()
+#
+#   quilt mode                          normal              quiltmode
+#                                       (eg linear)         _splitbrain
+#
+#   ------------      ------------------------------------------------
+#
+#   no split          no q cache        no q cache          forbidden,
+#     brain           PM on master      q fixup on master   prevented
+#   !$do_split_brain                    PM on master
+#
+#   split brain       no q cache        q fixup cached, to dgit view
+#                     PM in dgit view   PM in dgit view
+#
+# PM = pseudomerge to make ff, due to overwrite (or split view)
+# "no q cache" = do not record in cache on build, do not check cache
+# `3.0 (quilt)' with --quilt=nocheck is treated as sane format
+
 END {
     local ($@, $?);
     return unless forkcheck_mainprocess();