git-debrebase(5): Document commit message annotations

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

1 files changed, 17 insertions, 0 deletions

diff --git a/git-debrebase b/git-debrebase
index cdd6348..5b2312d 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -438,6 +438,23 @@ sub classify ($) {
 	# multi-orig upstreams are represented with an anchor merge
 	# from a single upstream commit which combines the orig tarballs
 
+	# Every anchor tagged this way must be a merge.
+	# We are relying on the
+	#     [git-debrebase anchor: ...]
+	# commit message annotation in "declare" anchor merges (which
+	# do not have any upstream changes), to distinguish those
+	# anchor merges from ordinary pseudomerges (which we might
+	# just try to strip).
+	#
+	# However, the user is going to be doing git-rebase a lot.  We
+	# really don't want them to rewrite an anchor commit.
+	# git-rebase trips up on merges, so that is a useful safety
+	# catch.
+	#
+	# BreakwaterStart commits are also anchors in the terminology
+	# of git-debrebase(5), but they are untagged (and always
+	# manually generated).
+
 	my $badanchor = sub { $unknown->("git-debrebase \`anchor' but @_"); };
 	@p == 2 or return $badanchor->("has other than two parents");
 	$haspatches and return $badanchor->("contains debian/patches");