pack-objects: Allow missing base objects when creating thin packs

If we are building a thin pack and one of the base objects we would
consider for deltification is missing its OK, the other side already
has that base object.  We may be able to get a delta from another
object, or we can simply send the new object whole (no delta).

This change allows a shallow clone to store only the objects which
are unique to it, as well as the boundary commit and its trees, but
avoids storing the boundary blobs.  This special form of a shallow
clone is able to represent just the difference between two trees.

Pack objects change suggested by Nicolas Pitre.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 2dadec1..b43e0b8 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1096,9 +1096,12 @@ static void check_object(struct object_entry *entry)
 	}
 
 	entry->type = sha1_object_info(entry->idx.sha1, &entry->size);
-	if (entry->type < 0)
-		die("unable to get type of object %s",
-		    sha1_to_hex(entry->idx.sha1));
+	/*
+	 * The error condition is checked in prepare_pack().  This is
+	 * to permit a missing preferred base object to be ignored
+	 * as a preferred base.  Doing so can result in a larger
+	 * pack file, but the transfer will still take place.
+	 */
 }
 
 static int pack_offset_sort(const void *_a, const void *_b)
@@ -1722,8 +1725,12 @@ static void prepare_pack(int window, int depth)
 		if (entry->no_try_delta)
 			continue;
 
-		if (!entry->preferred_base)
+		if (!entry->preferred_base) {
 			nr_deltas++;
+			if (entry->type < 0)
+				die("unable to get type of object %s",
+				    sha1_to_hex(entry->idx.sha1));
+		}
 
 		delta_list[n++] = entry;
 	}