Re: [PATCH v2 7/8] midx: replace `get_midx_rev_filename()` with a generic helper

> Commit f894081deae (pack-revindex: read multi-pack reverse indexes,
> 2021-03-30) introduced the `get_midx_rev_filename()` helper (later
> modified by commit 60980aed786 (midx.c: write MIDX filenames to
> strbuf, 2021-10-26)).
> 
> This function returns the location of the classic ".rev" files we used
> to write for MIDXs (prior to 95e8383bac1 (midx.c: make changing the
> preferred pack safe, 2022-01-25)), which is always of the form:
> 
>     $GIT_DIR/objects/pack/multi-pack-index-$HASH.rev
> 
> Replace this function with a generic helper that populates a strbuf with
> the above form, replacing the ".rev" extension with a caller-provided
> argument.

> +void get_midx_filename_ext(struct strbuf *out, const char *object_dir,
> +			   const unsigned char *hash, const char *ext)
>  {
>  	strbuf_addf(out, "%s/pack/multi-pack-index", object_dir);
> -}
> -
> -void get_midx_rev_filename(struct strbuf *out, struct multi_pack_index *m)
> -{
> -	get_midx_filename(out, m->object_dir);
> -	strbuf_addf(out, "-%s.rev", hash_to_hex(get_midx_checksum(m)));
> +	if (ext)
> +		strbuf_addf(out, "-%s.%s", hash_to_hex(hash), ext);
>  }