Subject: [RFC PATCH 01/14] midx: use `string_list` for retained MIDX files

From: Taylor Blau <[email-masked]>
Date: Tue, 24 Feb 2026 19:20:56 -0500

Both `clear_midx_files_ext()` and `clear_incremental_midx_files_ext()`
build a list of filenames to keep while pruning stale MIDX files. Today
they hand-roll an array instead of using a `string_list`, thus requiring
us to pass an additional length parameter, and makes lookups linear.

Replace the bare array with a `string_list` which can be passed around
as a single parameter. Though it improves lookup performance, the
difference is likely immeasurable given how small the keep_hashes array
typically is.

Signed-off-by: Taylor Blau <[email-masked]>
---
 midx.c | 56 ++++++++++++++++++++++----------------------------------
 1 file changed, 22 insertions(+), 34 deletions(-)

diff --git a/midx.c b/midx.c
index c1b9658240d..c5e3553e2bb 100644
--- a/midx.c
+++ b/midx.c
@@ -755,8 +755,7 @@ int midx_checksum_valid(struct multi_pack_index *m)
 }
 
 struct clear_midx_data {
-	char **keep;
-	uint32_t keep_nr;
+	struct string_list keep;
 	const char *ext;
 };
 
@@ -764,15 +763,12 @@ static void clear_midx_file_ext(const char *full_path, size_t full_path_len UNUS
 				const char *file_name, void *_data)
 {
 	struct clear_midx_data *data = _data;
-	uint32_t i;
 
 	if (!(starts_with(file_name, "multi-pack-index-") &&
 	      ends_with(file_name, data->ext)))
 		return;
-	for (i = 0; i < data->keep_nr; i++) {
-		if (!strcmp(data->keep[i], file_name))
-			return;
-	}
+	if (string_list_has_string(&data->keep, file_name))
+		return;
 	if (unlink(full_path))
 		die_errno(_("failed to remove %s"), full_path);
 }
@@ -780,48 +776,40 @@ static void clear_midx_file_ext(const char *full_path, size_t full_path_len UNUS
 void clear_midx_files_ext(struct odb_source *source, const char *ext,
 			  const char *keep_hash)
 {
-	struct clear_midx_data data;
-	memset(&data, 0, sizeof(struct clear_midx_data));
-
-	if (keep_hash) {
-		ALLOC_ARRAY(data.keep, 1);
-
-		data.keep[0] = xstrfmt("multi-pack-index-%s.%s", keep_hash, ext);
-		data.keep_nr = 1;
-	}
-	data.ext = ext;
-
-	for_each_file_in_pack_dir(source->path,
-				  clear_midx_file_ext,
-				  &data);
+	struct clear_midx_data data = {
+		.keep = STRING_LIST_INIT_NODUP,
+		.ext = ext,
+	};
 
 	if (keep_hash)
-		free(data.keep[0]);
-	free(data.keep);
+		string_list_insert(&data.keep, xstrfmt("multi-pack-index-%s.%s",
+						       keep_hash, ext));
+
+	for_each_file_in_pack_dir(source->path, clear_midx_file_ext, &data);
+
+	string_list_clear(&data.keep, 0);
 }
 
 void clear_incremental_midx_files_ext(struct odb_source *source, const char *ext,
 				      char **keep_hashes,
 				      uint32_t hashes_nr)
 {
-	struct clear_midx_data data;
+	struct clear_midx_data data = {
+		.keep = STRING_LIST_INIT_NODUP,
+		.ext = ext,
+	};
 	uint32_t i;
 
-	memset(&data, 0, sizeof(struct clear_midx_data));
-
-	ALLOC_ARRAY(data.keep, hashes_nr);
 	for (i = 0; i < hashes_nr; i++)
-		data.keep[i] = xstrfmt("multi-pack-index-%s.%s", keep_hashes[i],
-				       ext);
-	data.keep_nr = hashes_nr;
-	data.ext = ext;
+		string_list_append(&data.keep,
+				   xstrfmt("multi-pack-index-%s.%s",
+					   keep_hashes[i], ext));
+	string_list_sort(&data.keep);
 
 	for_each_file_in_pack_subdir(source->path, "multi-pack-index.d",
 				     clear_midx_file_ext, &data);
 
-	for (i = 0; i < hashes_nr; i++)
-		free(data.keep[i]);
-	free(data.keep);
+	string_list_clear(&data.keep, 0);
 }
 
 void clear_midx_file(struct repository *r)
-- 
2.53.0.185.g29bc4dff628