builtin/repack.c: use a string_list for 'midx_pack_names'

When writing a new MIDX, repack must determine whether or not there are
any packs in the MIDX it is replacing (if one exists) that are not
somehow represented in the new MIDX (e.g., either by preserving the pack
verbatim, or rolling it up as part of a geometric repack, etc.).

In order to do this, it keeps track of a list of pack names from the
MIDX present in the repository at the start of the repack operation.
Since we manipulate and close the object store, we cannot rely on the
repository's in-core representation of the MIDX, since this is subject
to change and/or go away.

When this behavior was introduced in 5ee86c2 (repack: exclude cruft
pack(s) from the MIDX where possible, 2025-06-23), we maintained an
array of character pointers instead of using a convenience API, such as
string-list.h.

Store the list of MIDX pack names in a string_list, thereby reducing the
number of parameters we have to pass to `midx_has_unknown_packs()`.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

builtin/repack.c

@@ -118,18 +118,17 @@ struct repack_write_midx_opts {
 	int midx_must_contain_cruft;
 };
 
-static int midx_has_unknown_packs(char **midx_pack_names,
-				  size_t midx_pack_names_nr,
+static int midx_has_unknown_packs(struct string_list *midx_pack_names,
 				  struct string_list *include,
 				  struct pack_geometry *geometry,
 				  struct existing_packs *existing)
 {
-	size_t i;
+	struct string_list_item *item;
 
 	string_list_sort(include);
 
-	for (i = 0; i < midx_pack_names_nr; i++) {
-		const char *pack_name = midx_pack_names[i];
+	for_each_string_list_item(item, midx_pack_names) {
+		const char *pack_name = item->string;
 
 		/*
 		 * Determine whether or not each MIDX'd pack from the existing
@@ -191,8 +190,7 @@ static int midx_has_unknown_packs(char **midx_pack_names,
 
 static void midx_included_packs(struct string_list *include,
 				struct existing_packs *existing,
-				char **midx_pack_names,
-				size_t midx_pack_names_nr,
+				struct string_list *midx_pack_names,
 				struct string_list *names,
 				struct pack_geometry *geometry)
 {
@@ -247,8 +245,8 @@ static void midx_included_packs(struct string_list *include,
 	}
 
 	if (midx_must_contain_cruft ||
-	    midx_has_unknown_packs(midx_pack_names, midx_pack_names_nr,
-				   include, geometry, existing)) {
+	    midx_has_unknown_packs(midx_pack_names, include, geometry,
+				   existing)) {
 		/*
 		 * If there are one or more unknown pack(s) present (see
 		 * midx_has_unknown_packs() for what makes a pack
@@ -606,13 +604,12 @@ int cmd_repack(int argc,
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	struct string_list_item *item;
 	struct string_list names = STRING_LIST_INIT_DUP;
+	struct string_list midx_pack_names = STRING_LIST_INIT_DUP;
 	struct existing_packs existing = EXISTING_PACKS_INIT;
 	struct pack_geometry geometry = { 0 };
 	struct tempfile *refs_snapshot = NULL;
 	int i, ret;
 	int show_progress;
-	char **midx_pack_names = NULL;
-	size_t midx_pack_names_nr = 0;
 
 	/* variables to be filled by option parsing */
 	struct repack_config_ctx config_ctx;
@@ -985,13 +982,12 @@ int cmd_repack(int argc,
 		struct multi_pack_index *m =
 			get_multi_pack_index(repo->objects->sources);
 
-		ALLOC_ARRAY(midx_pack_names,
-			    m->num_packs + m->num_packs_in_base);
-
-		for (; m; m = m->base_midx)
-			for (uint32_t i = 0; i < m->num_packs; i++)
-				midx_pack_names[midx_pack_names_nr++] =
-					xstrdup(m->pack_names[i]);
+		for (; m; m = m->base_midx) {
+			for (uint32_t i = 0; i < m->num_packs; i++) {
+				string_list_append(&midx_pack_names,
+						   m->pack_names[i]);
+			}
+		}
 	}
 
 	close_object_store(repo->objects);
@@ -1019,8 +1015,8 @@ int cmd_repack(int argc,
 			.write_bitmaps = write_bitmaps > 0,
 			.midx_must_contain_cruft = midx_must_contain_cruft
 		};
-		midx_included_packs(&include, &existing, midx_pack_names,
-				    midx_pack_names_nr, &names, &geometry);
+		midx_included_packs(&include, &existing, &midx_pack_names,
+				    &names, &geometry);
 
 		ret = write_midx_included_packs(&opts);
 
@@ -1067,11 +1063,9 @@ int cmd_repack(int argc,
 cleanup:
 	string_list_clear(&keep_pack_list, 0);
 	string_list_clear(&names, 1);
+	string_list_clear(&midx_pack_names, 0);
 	existing_packs_release(&existing);
 	pack_geometry_release(&geometry);
-	for (size_t i = 0; i < midx_pack_names_nr; i++)
-		free(midx_pack_names[i]);
-	free(midx_pack_names);
 	pack_objects_args_release(&po_args);
 	pack_objects_args_release(&cruft_po_args);