Re: [PATCH 1/9] odb: compute compat object ID in `odb_write_object_ext()`

> Repositories can have a compatibility hash configured, which means that
> such a repository is expected to maintain a mapping between canonical
> and compatibility object hashes. Maintaining this mapping is the
> responsibility of the object database sources, where we either store
> them as part of the loose objects map or in packfile indices v3 (once we
> gain support for this feature).

> But besides storing these compatibility hashes, the sources are also
> responsible for generating the compatibility hash in the first place.
> This is somewhat unnecessary though, as the compatibility hash should be
> computed the same no matter which source is being used. The consequence
> is that we need to duplicate this functionality across the different
> backends, which does not make a lot of sense.

> Refactor the code so that we instead compute the compatibility hash in
> `odb_write_object_ext()` and then pass the computed value to the
> sources. No callers need adjustment as there are none that write objects
> via the source interfaces directly.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  odb.c                 | 26 ++++++++++++++++++++++++--
>  odb.h                 | 10 ++++++----
>  odb/source-files.c    |  2 +-
>  odb/source-inmemory.c |  2 +-
>  odb/source-loose.c    | 24 +++---------------------
>  odb/source-packed.c   |  2 +-
>  odb/source.h          |  4 ++--
>  7 files changed, 38 insertions(+), 32 deletions(-)
> 
> diff --git a/odb.c b/odb.c
> index cf6e7938c0..1d6538163b 100644
> --- a/odb.c
> +++ b/odb.c
> @@ -989,11 +989,33 @@ int odb_write_object_ext(struct object_database *odb,
>  			 const void *buf, unsigned long len,
>  			 enum object_type type,
>  			 struct object_id *oid,
> -			 struct object_id *compat_oid,
> +			 const struct object_id *compat_oid_in,
>  			 enum odb_write_object_flags flags)
>  {
> +	const struct git_hash_algo *compat = odb->repo->compat_hash_algo;
> +	struct object_id compat_oid, *compat_oid_p = NULL;
> +
> +	if (compat) {
> +		const struct git_hash_algo *algo = odb->repo->hash_algo;
> +
> +		if (compat_oid_in) {
> +			oidcpy(&compat_oid, compat_oid_in);
> +		} else if (type == OBJ_BLOB) {
> +			hash_object_file(compat, buf, len, type, &compat_oid);
> +		} else {
> +			struct strbuf converted = STRBUF_INIT;
> +			convert_object_file(odb->repo, &converted, algo, compat,
> +					    buf, len, type, 0);
> +			hash_object_file(compat, converted.buf, converted.len,
> +					 type, &compat_oid);
> +			strbuf_release(&converted);
> +		}
> +
> +		compat_oid_p = &compat_oid;
> +	}