odb/source: introduce source type for robustness

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.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/odb/source.h b/odb/source.h
index e6698b73a3..45b72b81a0 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -1,6 +1,17 @@
 #ifndef ODB_SOURCE_H
 #define ODB_SOURCE_H
 
+enum odb_source_type {
+	/*
+	 * The "unknown" type, which should never be in use. This type 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 +30,9 @@ 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 +72,7 @@ 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);