Re: [PATCH v2 02/10] builtin/cat-file: wire up an option to filter objects

> In batch mode, git-cat-file(1) enumerates all objects and prints them
> by iterating through both loose and packed objects. This works without
> considering their reachability at all, and consequently most options to
> filter objects as they exist in e.g. git-rev-list(1) are not applicable.
> In some situations it may still be useful though to filter objects based
> on properties that are inherent to them. This includes the object size
> as well as its type.
>
> Such a filter already exists in git-rev-list(1) with the `--filter=`
> command line option. While this option supports a couple of filters that
> are not applicable to our usecase, some of them are quite a neat fit.
>
> Wire up the filter as an option for git-cat-file(1). This allows us to
> reuse the same syntax as in git-rev-list(1) so that we don't have to
> reinvent the wheel. For now, we die when any of the filter options has
> been passed by the user, but they will be wired up in subsequent
> commits.
>
> Further note that the filters that we are about to introduce don't
> significantly speed up the runtime of git-cat-file(1). While we can skip
> emitting a lot of objects in case they are uninteresting to us, the
> majority of time is spent reading the packfile, which is bottlenecked by
> I/O and not the processor. This will change though once we start to make
> use of bitmaps, which will allow us to skip reading the whole packfile.
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  Documentation/git-cat-file.adoc |  6 ++++++
>  builtin/cat-file.c              | 37 +++++++++++++++++++++++++++++++++----
>  t/t1006-cat-file.sh             | 32 ++++++++++++++++++++++++++++++++
>  3 files changed, 71 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/git-cat-file.adoc b/Documentation/git-cat-file.adoc
> index d5890ae3686..f7f57b7f538 100644
> --- a/Documentation/git-cat-file.adoc
> +++ b/Documentation/git-cat-file.adoc
> @@ -81,6 +81,12 @@ OPTIONS
>  	end-of-line conversion, etc). In this case, `<object>` has to be of
>  	the form `<tree-ish>:<path>`, or `:<path>`.
>  
> +--filter=<filter-spec>::
> +--no-filter::
> +	Omit objects from the list of printed objects. This can only be used in
> +	combination with one of the batched modes. The '<filter-spec>' may be
> +	one of the following:
> +
>  --path=<path>::
>  	For use with `--textconv` or `--filters`, to allow specifying an object
>  	name and a path separately, e.g. when it is difficult to figure out
> diff --git a/builtin/cat-file.c b/builtin/cat-file.c
> index 8e40016dd24..940900d92ad 100644
> --- a/builtin/cat-file.c
> +++ b/builtin/cat-file.c
> @@ -936,10 +946,13 @@ int cmd_cat_file(int argc,
>  	int opt_cw = 0;
>  	int opt_epts = 0;
>  	const char *exp_type = NULL, *obj_name = NULL;
> -	struct batch_options batch = {0};
> +	struct batch_options batch = {
> +		.objects_filter = LIST_OBJECTS_FILTER_INIT,
> +	};
>  	int unknown_type = 0;
>  	int input_nul_terminated = 0;
>  	int nul_terminated = 0;
> +	int ret;
>  
>  	const char * const builtin_catfile_usage[] = {
>  		N_("git cat-file <type> <object>"),
> @@ -1000,6 +1013,8 @@ int cmd_cat_file(int argc,
>  			    N_("run filters on object's content"), 'w'),
>  		OPT_STRING(0, "path", &force_path, N_("blob|tree"),
>  			   N_("use a <path> for (--textconv | --filters); Not with 'batch'")),
> +		OPT_CALLBACK(0, "filter", &batch.objects_filter, N_("args"),
> +			     N_("object filtering"), opt_parse_list_objects_filter),