Re: [GSoC PATCH v5 2/5] repo: add the field references.format

> This commit is part of the series that introduces the new subcommand
> git-repo-info.
> 
> The flag `--show-ref-format` from git-rev-parse is used for retrieving
> the reference format (i.e. `files` or `reftable`). This way, it is
> used for querying repository metadata, fitting in the purpose of
> git-repo-info.
> 
> Then, add a new field `references.format` to the repo-info subcommand
> containing that information.
> 
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Helped-by: Junio C Hamano <gitster@pobox.com>
> Helped-by: Justin Tobler <jltobler@gmail.com>
> Mentored-by: Karthik Nayak <karthik.188@gmail.com>
> Mentored-by: Patrick Steinhardt <ps@pks.im>
> Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
> ---
>  Documentation/git-repo.adoc |  4 ++
>  builtin/repo.c              | 75 ++++++++++++++++++++++++++++++++++++-
>  t/meson.build               |  1 +
>  t/t1900-repo.sh             | 50 +++++++++++++++++++++++++
>  4 files changed, 128 insertions(+), 2 deletions(-)
>  create mode 100755 t/t1900-repo.sh
> 
> diff --git a/Documentation/git-repo.adoc b/Documentation/git-repo.adoc
> index caee7d8aef..cf8483ec49 100644
> --- a/Documentation/git-repo.adoc
> +++ b/Documentation/git-repo.adoc
> @@ -29,6 +29,10 @@ INFO KEYS
>  The set of data that `git repo` can return is grouped into the following
>  categories:
>  
> +`references`::
> +Reference-related data:
> +* `format`: the reference storage format
> +
>  SEE ALSO
>  --------
>  linkgit:git-rev-parse[1]
> diff --git a/builtin/repo.c b/builtin/repo.c
> index d4f01e35e2..5beae0f781 100644
> --- a/builtin/repo.c
> +++ b/builtin/repo.c
> @@ -1,12 +1,83 @@
>  #include "builtin.h"
>  #include "parse-options.h"
> +#include "refs.h"
>  
> -static int repo_info(int argc UNUSED, const char **argv UNUSED,
> -		     const char *prefix UNUSED, struct repository *repo UNUSED)
> +typedef const char *get_value_fn(struct repository *repo);
> +
> +struct field {
> +	const char *key;
> +	get_value_fn *add_field_callback;
> +};
> +
> +static const char *get_references_format(struct repository *repo)
> +{
> +	return ref_storage_format_to_name(repo->ref_storage_format);
> +}
> +
> +/* repo_info_fields keys should be in lexicographical order */
> +static const struct field repo_info_fields[] = {
> +	{ "references.format", get_references_format },
> +};

> +
> +static int repo_info_fields_cmp(const void *va, const void *vb)
> +{
> +	const struct field *a = va;
> +	const struct field *b = vb;
> +
> +	return strcmp(a->key, b->key);
> +}
> +
> +static get_value_fn *get_value_callback(const char *key)
>  {
> +	const struct field search_key = { key, NULL };
> +	const struct field *found = bsearch(&search_key, repo_info_fields,
> +					    ARRAY_SIZE(repo_info_fields),
> +					    sizeof(struct field),
> +					    repo_info_fields_cmp);
> +	return found ? found->add_field_callback : NULL;
> +}
> +
> +static int qsort_strcmp(const void *va, const void *vb)
> +{
> +	const char *a = *(const char **)va;
> +	const char *b = *(const char **)vb;
> +
> +	return strcmp(a, b);
> +}
> +
> +static int print_fields(int argc, const char **argv, struct repository *repo)
> +{
> +	const char *last = "";
> +
> +	QSORT(argv, argc, qsort_strcmp);
> +
> +	for (int i = 0; i < argc; i++) {
> +		get_value_fn *callback;
> +		const char *key = argv[i];
> +		const char *value;
> +
> +		if (!strcmp(key, last))
> +			continue;
> +
> +		callback = get_value_callback(key);
> +
> +		if (!callback)
> +			return error("key %s not found", key);
> +
> +		value = callback(repo);
> +		printf("%s=%s\n", key, value);
> +		last = key;
> +	}

> +
>  	return 0;
>  }
>  
> +static int repo_info(int argc, const char **argv, const char *prefix UNUSED,
> +		     struct repository *repo)
> +{
> +	return print_fields(argc - 1, argv + 1, repo);
> +}
> +
>  int cmd_repo(int argc, const char **argv, const char *prefix,
>  	     struct repository *repo)
>  {