odb: introduce generic `odb_find_abbrev_len()`

Introduce a new generic `odb_find_abbrev_len()` function as well as
source-specific callback functions. This makes the logic to compute the
required prefix length to make a given object unique fully pluggable.

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

1 files changed, 24 insertions, 0 deletions

diff --git a/odb/source.h b/odb/source.h
index ee5d6ed530..a9d7d0b96f 100644
--- a/odb/source.h
+++ b/odb/source.h
@@ -158,6 +158,18 @@ struct odb_source {
 			     unsigned long *out);
 
 	/*
+	 * This callback is expected to find the minimum required length to
+	 * make the given object ID unique.
+	 *
+	 * The callback is expected to return a negative error code in case it
+	 * failed, 0 otherwise.
+	 */
+	int (*find_abbrev_len)(struct odb_source *source,
+			       const struct object_id *oid,
+			       unsigned min_length,
+			       unsigned *out);
+
+	/*
 	 * This callback is expected to freshen the given object so that its
 	 * last access time is set to the current time. This is used to ensure
 	 * that objects that are recent will not get garbage collected even if
@@ -361,6 +373,18 @@ static inline int odb_source_count_objects(struct odb_source *source,
 }
 
 /*
+ * Determine the minimum required length to make the given object ID unique in
+ * the given source. Returns 0 on success, a negative error code otherwise.
+ */
+static inline int odb_source_find_abbrev_len(struct odb_source *source,
+					     const struct object_id *oid,
+					     unsigned min_len,
+					     unsigned *out)
+{
+	return source->find_abbrev_len(source, oid, min_len, out);
+}
+
+/*
  * Freshen an object in the object database by updating its timestamp.
  * Returns 1 in case the object has been freshened, 0 in case the object does
  * not exist.