repack: move find_pack_prefix() out of the builtin

Both callers within the repack builtin which call functions that take a
'write_pack_opts' structure have the following pattern:

    struct write_pack_opts opts = {
        .packdir = packdir,
        .packtmp = packtmp,
        .pack_prefix = find_pack_prefix(packdir, packtmp),
        /* ... */
    };
    int ret = write_some_kind_of_pack(&opts, /* ... */);

, but both "packdir" and "packtmp" are fields within the write_pack_opts
struct itself!

Instead of also computing the pack_prefix ahead of time, let's have the
callees compute it themselves by moving `find_pack_prefix()` out of the
repack builtin, and have it take a write_pack_opts pointer instead of
the "packdir" and "packtmp" fields directly.

This avoids the callers having to do some prep work that is common
between the two of them, but also avoids the potential pitfall of
accidentally writing:

    .pack_prefix = find_pack_prefix(packtmp, packdir),

(which is well-typed) when the caller meant to instead write:

    .pack_prefix = find_pack_prefix(packdir, packtmp),

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

Author: ttaylorr

builtin/repack.c

@@ -149,6 +149,7 @@ static int write_filtered_pack(const struct write_pack_opts *opts,
 	const char *caret;
 	const char *scratch;
 	int local = skip_prefix(opts->destination, opts->packdir, &scratch);
+	const char *pack_prefix = write_pack_opts_pack_prefix(opts);
 
 	prepare_pack_objects(&cmd, opts->po_args, opts->destination);
 
@@ -173,7 +174,7 @@ static int write_filtered_pack(const struct write_pack_opts *opts,
 	 */
 	in = xfdopen(cmd.in, "w");
 	for_each_string_list_item(item, names)
-		fprintf(in, "^%s-%s.pack\n", opts->pack_prefix, item->string);
+		fprintf(in, "^%s-%s.pack\n", pack_prefix, item->string);
 	for_each_string_list_item(item, &existing->non_kept_packs)
 		fprintf(in, "%s.pack\n", item->string);
 	for_each_string_list_item(item, &existing->cruft_packs)
@@ -233,6 +234,7 @@ static int write_cruft_pack(const struct write_pack_opts *opts,
 	int ret;
 	const char *scratch;
 	int local = skip_prefix(opts->destination, opts->packdir, &scratch);
+	const char *pack_prefix = write_pack_opts_pack_prefix(opts);
 
 	prepare_pack_objects(&cmd, opts->po_args, opts->destination);
 
@@ -265,7 +267,7 @@ static int write_cruft_pack(const struct write_pack_opts *opts,
 	 */
 	in = xfdopen(cmd.in, "w");
 	for_each_string_list_item(item, names)
-		fprintf(in, "%s-%s.pack\n", opts->pack_prefix, item->string);
+		fprintf(in, "%s-%s.pack\n", pack_prefix, item->string);
 	if (combine_cruft_below_size && !cruft_expiration) {
 		combine_small_cruft_packs(in, combine_cruft_below_size,
 					  existing);
@@ -283,17 +285,6 @@ static int write_cruft_pack(const struct write_pack_opts *opts,
 				       local);
 }
 
-static const char *find_pack_prefix(const char *packdir, const char *packtmp)
-{
-	const char *pack_prefix;
-	if (!skip_prefix(packtmp, packdir, &pack_prefix))
-		die(_("pack prefix %s does not begin with objdir %s"),
-		    packtmp, packdir);
-	if (*pack_prefix == '/')
-		pack_prefix++;
-	return pack_prefix;
-}
-
 int cmd_repack(int argc,
 	       const char **argv,
 	       const char *prefix,
@@ -596,11 +587,9 @@ int cmd_repack(int argc,
 	}
 
 	if (pack_everything & PACK_CRUFT) {
-		const char *pack_prefix = find_pack_prefix(packdir, packtmp);
 		struct write_pack_opts opts = {
 			.po_args = &cruft_po_args,
 			.destination = packtmp,
-			.pack_prefix = pack_prefix,
 			.packtmp = packtmp,
 			.packdir = packdir,
 		};
@@ -667,7 +656,6 @@ int cmd_repack(int argc,
 		struct write_pack_opts opts = {
 			.po_args = &po_args,
 			.destination = filter_to,
-			.pack_prefix = find_pack_prefix(packdir, packtmp),
 			.packdir = packdir,
 			.packtmp = packtmp,
 		};

repack.c

@@ -66,6 +66,17 @@ void repack_remove_redundant_pack(struct repository *repo, const char *dir_name,
 	strbuf_release(&buf);
 }
 
+const char *write_pack_opts_pack_prefix(const struct write_pack_opts *opts)
+{
+	const char *pack_prefix;
+	if (!skip_prefix(opts->packtmp, opts->packdir, &pack_prefix))
+		die(_("pack prefix %s does not begin with objdir %s"),
+		    opts->packtmp, opts->packdir);
+	if (*pack_prefix == '/')
+		pack_prefix++;
+	return pack_prefix;
+}
+
 #define DELETE_PACK 1
 #define RETAIN_PACK 2
 

repack.h

@@ -35,11 +35,12 @@ void repack_remove_redundant_pack(struct repository *repo, const char *dir_name,
 struct write_pack_opts {
 	struct pack_objects_args *po_args;
 	const char *destination;
-	const char *pack_prefix;
 	const char *packdir;
 	const char *packtmp;
 };
 
+const char *write_pack_opts_pack_prefix(const struct write_pack_opts *opts);
+
 struct repository;
 struct packed_git;