From: Karthik Nayak <karthik.188@gmail.com>
Date: Thu, 05 Mar 2026 10:50:57 GMT
Subject: Re: [PATCH 05/17] odb/source: introduce source type for robustness
Message-ID: <CAOLa=ZR3cQjgdzF9_hRHSW6iO3p0qzduBBvO4-yTnc-1P-oFpg@mail.gmail.com>
In-Reply-To: <20260223-b4-pks-odb-source-pluggable-v1-5-253bac1db598@pks.im>

Patrick Steinhardt <ps@pks.im> writes:

> When a caller holds a `struct odb_source`, they have no way of telling
> what type the source is. This doesn't really cause any problems in the
> current status quo as we only have a single type anyway, "files". But
> going forward we expect to add more types, and if so it will become
> necessary to tell the sources apart.
>
> Introduce a new enum to cover this use case and assert that the given
> source actually matches the target source when performing the downcast.
>

So this is what I was talking about in a previous commit, nice to see.

> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  odb/source-files.c |  2 +-
>  odb/source-files.h |  2 ++
>  odb/source.c       |  2 ++
>  odb/source.h       | 16 ++++++++++++++++
>  4 files changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/odb/source-files.c b/odb/source-files.c
> index df0ea9ee62..7496e1d9f8 100644
> --- a/odb/source-files.c
> +++ b/odb/source-files.c
> @@ -36,7 +36,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
>  	struct odb_source_files *files;
>
>  	CALLOC_ARRAY(files, 1);
> -	odb_source_init(&files->base, odb, path, local);
> +	odb_source_init(&files->base, odb, ODB_SOURCE_FILES, path, local);
>  	files->loose = odb_source_loose_new(&files->base);
>  	files->packed = packfile_store_new(&files->base);
>
> diff --git a/odb/source-files.h b/odb/source-files.h
> index 58753d40de..803fa995fb 100644
> --- a/odb/source-files.h
> +++ b/odb/source-files.h
> @@ -30,6 +30,8 @@ void odb_source_files_free(struct odb_source_files *files);
>   */
>  static inline struct odb_source_files *odb_source_files_downcast(struct odb_source *source)
>  {
> +	if (source->type != ODB_SOURCE_FILES)
> +		BUG("trying to downcast source of type '%d' to files", source->type);
>  	return container_of(source, struct odb_source_files, base);
>  }
>
> diff --git a/odb/source.c b/odb/source.c
> index d8b2176a94..c7dcc528f6 100644
> --- a/odb/source.c
> +++ b/odb/source.c
> @@ -13,10 +13,12 @@ struct odb_source *odb_source_new(struct object_database *odb,
>
>  void odb_source_init(struct odb_source *source,
>  		     struct object_database *odb,
> +		     enum odb_source_type type,
>  		     const char *path,
>  		     bool local)
>  {
>  	source->odb = odb;
> +	source->type = type;
>  	source->local = local;
>  	source->path = xstrdup(path);
>  }
> diff --git a/odb/source.h b/odb/source.h
> index e6698b73a3..a1f2f8fdb1 100644
> --- a/odb/source.h
> +++ b/odb/source.h
> @@ -1,6 +1,18 @@
>  #ifndef ODB_SOURCE_H
>  #define ODB_SOURCE_H
>
> +enum odb_source_type {
> +	/*
> +	 * The "unknown" type, which should never be in use. This is type

Nit: s/is//

> +	 * mostly exists to catch cases where the type field remains zeroed
> +	 * out.
> +	 */
> +	ODB_SOURCE_UNKNOWN,
> +
> +	/* The "files" backend that uses loose objects and packfiles. */
> +	ODB_SOURCE_FILES,
> +};
> +
>  /*
>   * The source is the part of the object database that stores the actual
>   * objects. It thus encapsulates the logic to read and write the specific
> @@ -19,6 +31,9 @@ struct odb_source {
>  	/* Object database that owns this object source. */
>  	struct object_database *odb;
>
> +	/* The type used by this source. */
> +	enum odb_source_type type;
> +
>  	/*
>  	 * Figure out whether this is the local source of the owning
>  	 * repository, which would typically be its ".git/objects" directory.
> @@ -58,6 +73,7 @@ struct odb_source *odb_source_new(struct object_database *odb,
>   */
>  void odb_source_init(struct odb_source *source,
>  		     struct object_database *odb,
> +		     enum odb_source_type type,
>  		     const char *path,
>  		     bool local);
>
>
> --
> 2.53.0.536.g309c995771.dirty