[PATCH v2 7/8] repack: defer allocating the append plan's write step

[Taylor Blau <ttaylorr@openai.com>]

The append plan creates a write step before iterating over newly
written packs. The next change will consider additional packs and skip
those already covered by the MIDX chain, so a non-empty candidate list
will no longer imply that a write step is needed.

Allocate the step when adding its first pack instead. Continue to
consider only newly written packs here, preserving the existing plan.

Signed-off-by: Taylor Blau <ttaylorr@openai.com>
---
 repack-midx.c | 35 +++++++++++++++--------------------
 1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/repack-midx.c b/repack-midx.c
index 61832114671..06eadb9df82 100644
--- a/repack-midx.c
+++ b/repack-midx.c
@@ -559,33 +559,28 @@ static void repack_make_midx_append_plan(struct repack_write_midx_opts *opts,
 	struct odb_source_files *files = odb_source_files_downcast(opts->existing->source);
 	struct multi_pack_index *m;
 	struct midx_compaction_step *steps = NULL;
-	struct midx_compaction_step *step;
+	struct midx_compaction_step *step = NULL;
+	struct strbuf buf = STRBUF_INIT;
 	size_t steps_nr = 0, steps_alloc = 0;
+	uint32_t i;
 
 	odb_reprepare(opts->existing->repo->objects);
 	m = get_multi_pack_index(files->packed);
 
-	if (opts->names->nr) {
-		struct strbuf buf = STRBUF_INIT;
-		uint32_t i;
-
-		ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
-
-		step = &steps[steps_nr++];
-		memset(step, 0, sizeof(*step));
-
-		step->type = MIDX_COMPACTION_STEP_WRITE;
-		string_list_init_dup(&step->u.write);
-
-		for (i = 0; i < opts->names->nr; i++) {
-			strbuf_reset(&buf);
-			strbuf_addf(&buf, "pack-%s.idx",
-				    opts->names->items[i].string);
-			string_list_append(&step->u.write, buf.buf);
+	for (i = 0; i < opts->names->nr; i++) {
+		if (!step) {
+			ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
+			step = &steps[steps_nr++];
+			memset(step, 0, sizeof(*step));
+			step->type = MIDX_COMPACTION_STEP_WRITE;
+			string_list_init_dup(&step->u.write);
 		}
-
-		strbuf_release(&buf);
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "pack-%s.idx",
+			    opts->names->items[i].string);
+		string_list_append(&step->u.write, buf.buf);
 	}
+	strbuf_release(&buf);
 
 	for (; m; m = m->base_midx) {
 		ALLOC_GROW(steps, st_add(steps_nr, 1), steps_alloc);
-- 
2.56.0.8.ga42f775cbe2