[PATCH v2 10/16] repack-midx: extract `repack_fill_midx_stdin_packs()`

[Taylor Blau <me@ttaylorr.com>]

The function `write_midx_included_packs()` manages the lifecycle of
writing packs to stdin when running `git multi-pack-index write` as a
child process.

Extract a standalone `repack_fill_midx_stdin_packs()` helper, which
handles `--stdin-packs` argument setup, starting the command, writing
pack names to its standard input, and finishing the command.

This simplifies `write_midx_included_packs()` and prepares for a
subsequent commit where the same helper is called with `cmd->out = -1`
to capture the MIDX's checksum from the command's standard output,
which is needed when writing MIDX layers with `--checksum-only`.

No functional changes are included in this patch.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 repack-midx.c | 38 ++++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/repack-midx.c b/repack-midx.c
index 83151d4734a..78f069c2151 100644
--- a/repack-midx.c
+++ b/repack-midx.c
@@ -292,23 +292,42 @@ static void repack_prepare_midx_command(struct child_process *cmd,
 		strvec_push(&cmd->args, "--bitmap");
 }
 
+static int repack_fill_midx_stdin_packs(struct child_process *cmd,
+					struct string_list *include)
+{
+	struct string_list_item *item;
+	FILE *in;
+	int ret;
+
+	cmd->in = -1;
+
+	strvec_push(&cmd->args, "--stdin-packs");
+
+	ret = start_command(cmd);
+	if (ret)
+		return ret;
+
+	in = xfdopen(cmd->in, "w");
+	for_each_string_list_item(item, include)
+		fprintf(in, "%s\n", item->string);
+	fclose(in);
+
+	return finish_command(cmd);
+}
+
 int write_midx_included_packs(struct repack_write_midx_opts *opts)
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	struct string_list include = STRING_LIST_INIT_DUP;
 	struct string_list_item *item;
 	struct packed_git *preferred = pack_geometry_preferred_pack(opts->geometry);
-	FILE *in;
 	int ret = 0;
 
 	midx_included_packs(&include, opts);
 	if (!include.nr)
 		goto done;
 
-	cmd.in = -1;
-
 	repack_prepare_midx_command(&cmd, opts, "write");
-	strvec_push(&cmd.args, "--stdin-packs");
 
 	if (preferred)
 		strvec_pushf(&cmd.args, "--preferred-pack=%s",
@@ -350,16 +369,7 @@ int write_midx_included_packs(struct repack_write_midx_opts *opts)
 		strvec_pushf(&cmd.args, "--refs-snapshot=%s",
 			     opts->refs_snapshot);
 
-	ret = start_command(&cmd);
-	if (ret)
-		goto done;
-
-	in = xfdopen(cmd.in, "w");
-	for_each_string_list_item(item, &include)
-		fprintf(in, "%s\n", item->string);
-	fclose(in);
-
-	ret = finish_command(&cmd);
+	ret = repack_fill_midx_stdin_packs(&cmd, &include);
 done:
 	if (!ret && opts->write_bitmaps)
 		remove_redundant_bitmaps(&include, opts->packdir);
-- 
2.54.0.9.gb905fd5d0ae