[PATCH v2 1/4] midx: access pack names through `nth_midxed_pack_name()`

[Taylor Blau <me@xxxxxxxxxxxx>]

Accessing a MIDX's 'pack_names' array is somewhat error-prone when
dealing with incremental MIDX chains, where the (global) pack_int_id for
some pack may differ from the containing layer's index for that pack.

Introduce `nth_midxed_pack_name()` in an effort to reduce a common
source of errors by discouraging external callers from accessing a
layer's `pack_names` array directly.

Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
 midx.c                    | 7 +++++++
 midx.h                    | 2 ++
 pack-bitmap.c             | 4 ++--
 t/helper/test-read-midx.c | 7 ++++---
 4 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/midx.c b/midx.c
index cd6e766ce2..6705e77881 100644
--- a/midx.c
+++ b/midx.c
@@ -506,6 +506,13 @@ struct packed_git *nth_midxed_pack(struct multi_pack_index *m,
 	return m->packs[local_pack_int_id];
 }
 
+const char *nth_midxed_pack_name(struct multi_pack_index *m,
+				 uint32_t pack_int_id)
+{
+	uint32_t local_pack_int_id = midx_for_pack(&m, pack_int_id);
+	return m->pack_names[local_pack_int_id];
+}
+
 #define MIDX_CHUNK_BITMAPPED_PACKS_WIDTH (2 * sizeof(uint32_t))
 
 int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
diff --git a/midx.h b/midx.h
index 9d1374cbd5..0fb490f4d4 100644
--- a/midx.h
+++ b/midx.h
@@ -107,6 +107,8 @@ struct multi_pack_index *load_multi_pack_index(struct repository *r,
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
 struct packed_git *nth_midxed_pack(struct multi_pack_index *m,
 				   uint32_t pack_int_id);
+const char *nth_midxed_pack_name(struct multi_pack_index *m,
+				 uint32_t pack_int_id);
 int nth_bitmapped_pack(struct repository *r, struct multi_pack_index *m,
 		       struct bitmapped_pack *bp, uint32_t pack_int_id);
 int bsearch_one_midx(const struct object_id *oid, struct multi_pack_index *m,
diff --git a/pack-bitmap.c b/pack-bitmap.c
index b9f1d86604..8ddc150778 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -490,7 +490,7 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	for (i = 0; i < bitmap_git->midx->num_packs + bitmap_git->midx->num_packs_in_base; i++) {
 		if (prepare_midx_pack(bitmap_repo(bitmap_git), bitmap_git->midx, i)) {
 			warning(_("could not open pack %s"),
-				bitmap_git->midx->pack_names[i]);
+				nth_midxed_pack_name(bitmap_git->midx, i));
 			goto cleanup;
 		}
 	}
@@ -2469,7 +2469,7 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 			struct bitmapped_pack pack;
 			if (nth_bitmapped_pack(r, bitmap_git->midx, &pack, i) < 0) {
 				warning(_("unable to load pack: '%s', disabling pack-reuse"),
-					bitmap_git->midx->pack_names[i]);
+					nth_midxed_pack_name(bitmap_git->midx, i));
 				free(packs);
 				return;
 			}
diff --git a/t/helper/test-read-midx.c b/t/helper/test-read-midx.c
index ac81390899..fbed0f6919 100644
--- a/t/helper/test-read-midx.c
+++ b/t/helper/test-read-midx.c
@@ -53,8 +53,9 @@ static int read_midx_file(const char *object_dir, const char *checksum,
 	printf("\nnum_objects: %d\n", m->num_objects);
 
 	printf("packs:\n");
-	for (i = 0; i < m->num_packs; i++)
-		printf("%s\n", m->pack_names[i]);
+	for (i = m->num_packs_in_base; i < m->num_packs + m->num_packs_in_base;
+	     i++)
+		printf("%s\n", nth_midxed_pack_name(m, i));
 
 	printf("object-dir: %s\n", m->object_dir);
 
@@ -108,7 +109,7 @@ static int read_midx_preferred_pack(const char *object_dir)
 		return 1;
 	}
 
-	printf("%s\n", midx->pack_names[preferred_pack]);
+	printf("%s\n", nth_midxed_pack_name(midx, preferred_pack));
 	close_midx(midx);
 	return 0;
 }
-- 
2.49.0.640.ga4de40e6a8