object-file: introduce function to iterate through objects

We have multiple divergent interfaces to iterate through objects of a
specific backend:

  - `for_each_loose_object()` yields all loose objects.

  - `for_each_packed_object()` (somewhat obviously) yields all packed
    objects.

These functions have different function signatures, which makes it hard
to create a common abstraction layer that covers both of these.

Introduce a new function `odb_source_loose_for_each_object()` to plug
this gap. This function doesn't take any data specific to loose objects,
but instead it accepts a `struct object_info` that will be populated the
exact same as if `odb_source_loose_read_object()` was called.

The benefit of this new interface is that we can continue to pass
backend-specific data, as `struct object_info` contains a union for
these exact use cases. This will allow us to unify how we iterate
through objects across both loose and packed objects in a subsequent
commit.

The `for_each_loose_object()` function continues to exist for now, but
it will be removed at the end of this patch series.

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

1 files changed, 12 insertions, 0 deletions

diff --git a/odb.h b/odb.h
index 74503addf1..f97f249580 100644
--- a/odb.h
+++ b/odb.h
@@ -463,6 +463,18 @@ enum odb_for_each_object_flags {
 	ODB_FOR_EACH_OBJECT_SKIP_ON_DISK_KEPT_PACKS = (1<<4),
 };
 
+/*
+ * A callback function that can be used to iterate through objects. If given,
+ * the optional `oi` parameter will be populated the same as if you would call
+ * `odb_read_object_info()`.
+ *
+ * Returning a non-zero error code will cause iteration to abort. The error
+ * code will be propagated.
+ */
+typedef int (*odb_for_each_object_cb)(const struct object_id *oid,
+				      struct object_info *oi,
+				      void *cb_data);
+
 enum {
 	/*
 	 * By default, `odb_write_object()` does not actually write anything