[PATCH] sha1_name: simplify strbuf handling in interpret_nth_prior_checkout()

[René Scharfe <l.s.r@xxxxxx>]

Pass the target strbuf to the callback function grab_nth_branch_switch()
by reference so that it can add the result string directly instead of
having it put the string into a temporary strbuf first.  This gets rid
of an extra allocation and a string copy.

Signed-off-by: René Scharfe <l.s.r@xxxxxx>
---
Patch formatted with --function-context for easier reviewing.

 sha1-name.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/sha1-name.c b/sha1-name.c
index c665e3f96d..85196929c7 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -1286,70 +1286,67 @@ static int get_oid_oneline(struct repository *r,

 struct grab_nth_branch_switch_cbdata {
 	int remaining;
-	struct strbuf buf;
+	struct strbuf *sb;
 };

 static int grab_nth_branch_switch(struct object_id *ooid, struct object_id *noid,
 				  const char *email, timestamp_t timestamp, int tz,
 				  const char *message, void *cb_data)
 {
 	struct grab_nth_branch_switch_cbdata *cb = cb_data;
 	const char *match = NULL, *target = NULL;
 	size_t len;

 	if (skip_prefix(message, "checkout: moving from ", &match))
 		target = strstr(match, " to ");

 	if (!match || !target)
 		return 0;
 	if (--(cb->remaining) == 0) {
 		len = target - match;
-		strbuf_reset(&cb->buf);
-		strbuf_add(&cb->buf, match, len);
+		strbuf_reset(cb->sb);
+		strbuf_add(cb->sb, match, len);
 		return 1; /* we are done */
 	}
 	return 0;
 }

 /*
  * Parse @{-N} syntax, return the number of characters parsed
  * if successful; otherwise signal an error with negative value.
  */
 static int interpret_nth_prior_checkout(struct repository *r,
 					const char *name, int namelen,
 					struct strbuf *buf)
 {
 	long nth;
 	int retval;
 	struct grab_nth_branch_switch_cbdata cb;
 	const char *brace;
 	char *num_end;

 	if (namelen < 4)
 		return -1;
 	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 		return -1;
 	brace = memchr(name, '}', namelen);
 	if (!brace)
 		return -1;
 	nth = strtol(name + 3, &num_end, 10);
 	if (num_end != brace)
 		return -1;
 	if (nth <= 0)
 		return -1;
 	cb.remaining = nth;
-	strbuf_init(&cb.buf, 20);
+	cb.sb = buf;

 	retval = refs_for_each_reflog_ent_reverse(get_main_ref_store(r),
 			"HEAD", grab_nth_branch_switch, &cb);
 	if (0 < retval) {
-		strbuf_reset(buf);
-		strbuf_addbuf(buf, &cb.buf);
 		retval = brace - name + 1;
 	} else
 		retval = 0;

-	strbuf_release(&cb.buf);
 	return retval;
 }

--
2.23.0