Re: [PATCH v2 1/8] builtin/clone: defer setup of the object database

> When cloning a repository we defer initialization of the reference
> database. This is because we don't yet know all details required for us
> to initialize the refdb in the first place. Most importantly, what we
> are missing is information about the object hash.
> 
> We don't do the same thing for the object database yet, but here we
> essentially have the same problem. While the "files" database does not
> need any information about the object format at creation time, alternate
> backends are likely to require that information so that they can
> properly set up their data structures.

> Besides this forward-looking future proofing though, we also have a
> second use case for deferring initialization of the object database,
> namely alternates. When initializing the object database we do not yet
> know whether we'll need alternates or not because this depends on the
> repository we're about to clone from. If it is a local repository and
> the user has passed "--refernce{,-if-able}", then we will end up writing
> alternates into the object database.
> 
> The ugly part though is that we cannot determine where the repository is
> getting cloned from before it has been initialized. While we of course
> already have access to the user-provided URI, that URI can be very well
> rewritten via "url.<base>.insteadOf". We can of course read the global-
> and system-level configuration to resolve it. But we explicitly resolve
> the URI a second time after we have initialized the repository because
> it can happen that we copy a ".git/config" over from our templates, and
> that file may cause us to rewrite the path.
> 
> In a subsequent commit though we'll start to write alternates as part of
> the repository initialization, so we'll need to have the URI properly
> resolved before we can initialize the object database. This is ugly, but
> as mentioned above it makes sense for us to defer its initialization
> anyway so that we also know about the object hash already.

> Introduce a new flag that makes `init_db()` skip initializing the object
> database. Expose `create_object_database()` and make use of it after we
> have resolved the URI.
> 
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  builtin/clone.c | 12 ++++++++----
>  setup.c         |  8 +++++---
>  setup.h         | 15 ++++++++++-----
>  3 files changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/builtin/clone.c b/builtin/clone.c
> index 5b25cca510..0a67492ebd 100644
> --- a/builtin/clone.c
> +++ b/builtin/clone.c
> @@ -1184,11 +1184,14 @@ int cmd_clone(int argc,
>  	 * database. We do not yet know about the object format of the
>  	 * repository, and reference backends may persist that information into
>  	 * their on-disk data structures.
> +	 *
> +	 * Furthermore, we skip initializing the object database so that we can
> +	 * first resolve potential alternates before creating it.
>  	 */
>  	init_db(the_repository, git_dir, real_git_dir, work_tree, option_template,
>  		GIT_HASH_UNKNOWN, ref_storage_format, NULL,
>  		do_not_override_repo_unix_permissions,
> -		INIT_DB_QUIET | INIT_DB_SKIP_REFDB);
> +		INIT_DB_QUIET | INIT_DB_SKIP_REFDB | INIT_DB_SKIP_ODB);

>  	if (real_git_dir) {
>  		free((char *)git_dir);
> @@ -1311,9 +1314,6 @@ int cmd_clone(int argc,
>  		strbuf_reset(&key);
>  	}
>  
> -	if (option_required_reference.nr || option_optional_reference.nr)
> -		setup_reference();
> -
>  	remote = remote_get_early(remote_name);
>  
>  	if (!option_rev)
> @@ -1342,6 +1342,10 @@ int cmd_clone(int argc,
>  	if (option_local > 0 && !is_local)
>  		warning(_("--local is ignored"));
>  
> +	create_object_database(the_repository);