git notes merge: Add another auto-resolving strategy: "cat_sort_uniq"

This new strategy is similar to "concatenate", but in addition to
concatenating the two note candidates, this strategy sorts the resulting
lines, and removes duplicate lines from the result. This is equivalent to
applying the "cat | sort | uniq" shell pipeline to the two note candidates.

This strategy is useful if the notes follow a line-based format where one
wants to avoid duplicate lines in the merge result.

Note that if either of the note candidates contain duplicate lines _prior_
to the merge, these will also be removed by this merge strategy.

The patch also contains tests and documentation for the new strategy.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/notes-merge.c b/notes-merge.c
index 459b1c2bf..71c4d45fc 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -453,6 +453,13 @@ static int merge_one_change(struct notes_merge_options *o,
 			die("failed to concatenate notes "
 			    "(combine_notes_concatenate)");
 		return 0;
+	case NOTES_MERGE_RESOLVE_CAT_SORT_UNIQ:
+		OUTPUT(o, 2, "Concatenating unique lines in local and remote "
+		       "notes for %s", sha1_to_hex(p->obj));
+		if (add_note(t, p->obj, p->remote, combine_notes_cat_sort_uniq))
+			die("failed to concatenate notes "
+			    "(combine_notes_cat_sort_uniq)");
+		return 0;
 	}
 	die("Unknown strategy (%i).", o->strategy);
 }