Merge branch 'tb/multi-pack-reuse-fix'

A data corruption bug when multi-pack-index is used and the same
objects are stored in multiple packfiles has been corrected.

* tb/multi-pack-reuse-fix:
  builtin/pack-objects.c: do not open-code `MAX_PACK_OBJECT_HEADER`
  pack-bitmap.c: avoid repeated `pack_pos_to_offset()` during reuse
  builtin/pack-objects.c: translate bit positions during pack-reuse
  pack-bitmap: tag bitmapped packs with their corresponding MIDX
  t/t5332-multi-pack-reuse.sh: verify pack generation with --strict

1 files changed, 37 insertions, 9 deletions

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 778be80f56..c6e2852d3c 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1072,7 +1072,7 @@ static void write_reused_pack_one(struct packed_git *reuse_packfile,
 		fixup = find_reused_offset(offset) -
 			find_reused_offset(base_offset);
 		if (fixup) {
-			unsigned char ofs_header[10];
+			unsigned char ofs_header[MAX_PACK_OBJECT_HEADER];
 			unsigned i, ofs_len;
 			off_t ofs = offset - base_offset - fixup;
 
@@ -1191,6 +1191,7 @@ static void write_reused_pack(struct bitmapped_pack *reuse_packfile,
 		size_t pos = (i * BITS_IN_EWORD);
 
 		for (offset = 0; offset < BITS_IN_EWORD; ++offset) {
+			uint32_t pack_pos;
 			if ((word >> offset) == 0)
 				break;
 
@@ -1199,14 +1200,41 @@ static void write_reused_pack(struct bitmapped_pack *reuse_packfile,
 				continue;
 			if (pos + offset >= reuse_packfile->bitmap_pos + reuse_packfile->bitmap_nr)
 				goto done;
-			/*
-			 * Can use bit positions directly, even for MIDX
-			 * bitmaps. See comment in try_partial_reuse()
-			 * for why.
-			 */
-			write_reused_pack_one(reuse_packfile->p,
-					      pos + offset - reuse_packfile->bitmap_pos,
-					      f, pack_start, &w_curs);
+
+			if (reuse_packfile->bitmap_pos) {
+				/*
+				 * When doing multi-pack reuse on a
+				 * non-preferred pack, translate bit positions
+				 * from the MIDX pseudo-pack order back to their
+				 * pack-relative positions before attempting
+				 * reuse.
+				 */
+				struct multi_pack_index *m = reuse_packfile->from_midx;
+				uint32_t midx_pos;
+				off_t pack_ofs;
+
+				if (!m)
+					BUG("non-zero bitmap position without MIDX");
+
+				midx_pos = pack_pos_to_midx(m, pos + offset);
+				pack_ofs = nth_midxed_offset(m, midx_pos);
+
+				if (offset_to_pack_pos(reuse_packfile->p,
+						       pack_ofs, &pack_pos) < 0)
+					BUG("could not find expected object at offset %"PRIuMAX" in pack %s",
+					    (uintmax_t)pack_ofs,
+					    pack_basename(reuse_packfile->p));
+			} else {
+				/*
+				 * Can use bit positions directly, even for MIDX
+				 * bitmaps. See comment in try_partial_reuse()
+				 * for why.
+				 */
+				pack_pos = pos + offset;
+			}
+
+			write_reused_pack_one(reuse_packfile->p, pack_pos, f,
+					      pack_start, &w_curs);
 			display_progress(progress_state, ++written);
 		}
 	}