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

[René Scharfe]

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....@web.de>
---
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