git-debrebase: comment: explain why tagged linear anchors are evil

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

1 files changed, 9 insertions, 0 deletions

diff --git a/git-debrebase b/git-debrebase
index fcca5b1..5246317 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -396,6 +396,15 @@ sub classify ($) {
 	# BreakwaterStart commits are also anchors in the terminology
 	# of git-debrebase(5), but they are untagged (and always
 	# manually generated).
+	#
+	# We cannot not tolerate any tagged linear commit (ie,
+	# BreakwaterStart commits tagged `[anchor:') because such a
+	# thing could result from an erroneous linearising raw git
+	# rebase of a merge anchor.  That would represent a corruption
+	# of the branch. and we want to detect and reject the results
+	# of such corruption before it makes it out anywhere.  If we
+	# reject it here then we avoid making the pseudomerge which
+	# would be needed to push it.
 
 	my $badanchor = sub { $unknown->("git-debrebase \`anchor' but @_"); };
 	@p == 2 or return $badanchor->("has other than two parents");