Merge branch 'ps/missing-btmp-fix'

GIt 2.44 introduced a regression that makes the updated code to
barf in repositories with multi-pack index written by older
versions of Git, which has been corrected.

* ps/missing-btmp-fix:
  pack-bitmap: gracefully handle missing BTMP chunks

Author: gitster

midx.c

@@ -170,9 +170,10 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 
 	pair_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets,
 		   &m->chunk_large_offsets_len);
-	pair_chunk(cf, MIDX_CHUNKID_BITMAPPEDPACKS,
-		   (const unsigned char **)&m->chunk_bitmapped_packs,
-		   &m->chunk_bitmapped_packs_len);
+	if (git_env_bool("GIT_TEST_MIDX_READ_BTMP", 1))
+		pair_chunk(cf, MIDX_CHUNKID_BITMAPPEDPACKS,
+			   (const unsigned char **)&m->chunk_bitmapped_packs,
+			   &m->chunk_bitmapped_packs_len);
 
 	if (git_env_bool("GIT_TEST_MIDX_READ_RIDX", 1))
 		pair_chunk(cf, MIDX_CHUNKID_REVINDEX, &m->chunk_revindex,

pack-bitmap.c

@@ -2049,7 +2049,10 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 
 	load_reverse_index(r, bitmap_git);
 
-	if (bitmap_is_midx(bitmap_git)) {
+	if (!bitmap_is_midx(bitmap_git) || !bitmap_git->midx->chunk_bitmapped_packs)
+		multi_pack_reuse = 0;
+
+	if (multi_pack_reuse) {
 		for (i = 0; i < bitmap_git->midx->num_packs; i++) {
 			struct bitmapped_pack pack;
 			if (nth_bitmapped_pack(r, bitmap_git->midx, &pack, i) < 0) {
@@ -2062,34 +2065,32 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 			if (!pack.bitmap_nr)
 				continue;
 
-			if (!multi_pack_reuse && pack.bitmap_pos) {
-				/*
-				 * If we're only reusing a single pack, skip
-				 * over any packs which are not positioned at
-				 * the beginning of the MIDX bitmap.
-				 *
-				 * This is consistent with the existing
-				 * single-pack reuse behavior, which only reuses
-				 * parts of the MIDX's preferred pack.
-				 */
-				continue;
-			}
-
 			ALLOC_GROW(packs, packs_nr + 1, packs_alloc);
 			memcpy(&packs[packs_nr++], &pack, sizeof(pack));
 
 			objects_nr += pack.p->num_objects;
-
-			if (!multi_pack_reuse)
-				break;
 		}
 
 		QSORT(packs, packs_nr, bitmapped_pack_cmp);
 	} else {
-		ALLOC_GROW(packs, packs_nr + 1, packs_alloc);
+		struct packed_git *pack;
+
+		if (bitmap_is_midx(bitmap_git)) {
+			uint32_t preferred_pack_pos;
+
+			if (midx_preferred_pack(bitmap_git->midx, &preferred_pack_pos) < 0) {
+				warning(_("unable to compute preferred pack, disabling pack-reuse"));
+				return;
+			}
 
-		packs[packs_nr].p = bitmap_git->pack;
-		packs[packs_nr].bitmap_nr = bitmap_git->pack->num_objects;
+			pack = bitmap_git->midx->packs[preferred_pack_pos];
+		} else {
+			pack = bitmap_git->pack;
+		}
+
+		ALLOC_GROW(packs, packs_nr + 1, packs_alloc);
+		packs[packs_nr].p = pack;
+		packs[packs_nr].bitmap_nr = pack->num_objects;
 		packs[packs_nr].bitmap_pos = 0;
 
 		objects_nr = packs[packs_nr++].bitmap_nr;

t/t5326-multi-pack-bitmaps.sh

@@ -513,4 +513,21 @@ test_expect_success 'corrupt MIDX with bitmap causes fallback' '
 	)
 '
 
+for allow_pack_reuse in single multi
+do
+	test_expect_success "reading MIDX without BTMP chunk does not complain with $allow_pack_reuse pack reuse" '
+		test_when_finished "rm -rf midx-without-btmp" &&
+		git init midx-without-btmp &&
+		(
+			cd midx-without-btmp &&
+			test_commit initial &&
+
+			git repack -Adbl --write-bitmap-index --write-midx &&
+			GIT_TEST_MIDX_READ_BTMP=false git -c pack.allowPackReuse=$allow_pack_reuse \
+				pack-objects --all --use-bitmap-index --stdout </dev/null >/dev/null 2>err &&
+			test_must_be_empty err
+		)
+	'
+done
+
 test_done