make pack-objects a bit more resilient to repo corruption

Right now, packing valid objects could fail when creating a thin pack
simply because a pack edge object used as a preferred base is corrupted.
Since preferred base objects are not strictly needed to produce a valid
pack, let's not consider the inability to read them as a fatal error.
Delta compression may well be attempted against other objects in the
search window.  To avoid warning storms (we are in the inner loop of
the delta search window) a warning is emitted only on the first
occurrence.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index f8eba53c82242d0c435524ab9ffab70ba2e2d5ad..3cbeb299d172c51b8ab6940a836efdf8a1a8e4ce 100644 (file)
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1298,9 +1298,23 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
                read_lock();
                src->data = read_sha1_file(src_entry->idx.sha1, &type, &sz);
                read_unlock();
-               if (!src->data)
+               if (!src->data) {
+                       if (src_entry->preferred_base) {
+                               static int warned = 0;
+                               if (!warned++)
+                                       warning("object %s cannot be read",
+                                               sha1_to_hex(src_entry->idx.sha1));
+                               /*
+                                * Those objects are not included in the
+                                * resulting pack.  Be resilient and ignore
+                                * them if they can't be read, in case the
+                                * pack could be created nevertheless.
+                                */
+                               return 0;
+                       }
                        die("object %s cannot be read",
                            sha1_to_hex(src_entry->idx.sha1));
+               }
                if (sz != src_size)
                        die("object %s inconsistent object length (%lu vs %lu)",
                            sha1_to_hex(src_entry->idx.sha1), sz, src_size);