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>

2 files changed, 49 insertions, 0 deletions

diff --git a/odb/source-files.c b/odb/source-files.c
index e90bb689bb..76797569de 100644
--- a/odb/source-files.c
+++ b/odb/source-files.c
@@ -122,6 +122,30 @@ out:
 	return ret;
 }
 
+static int odb_source_files_find_abbrev_len(struct odb_source *source,
+					    const struct object_id *oid,
+					    unsigned min_len,
+					    unsigned *out)
+{
+	struct odb_source_files *files = odb_source_files_downcast(source);
+	unsigned len = min_len;
+	int ret;
+
+	ret = packfile_store_find_abbrev_len(files->packed, oid, len, &len);
+	if (ret < 0)
+		goto out;
+
+	ret = odb_source_loose_find_abbrev_len(source, oid, len, &len);
+	if (ret < 0)
+		goto out;
+
+	*out = len;
+	ret = 0;
+
+out:
+	return ret;
+}
+
 static int odb_source_files_freshen_object(struct odb_source *source,
 					   const struct object_id *oid)
 {
@@ -250,6 +274,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 	files->base.read_object_stream = odb_source_files_read_object_stream;
 	files->base.for_each_object = odb_source_files_for_each_object;
 	files->base.count_objects = odb_source_files_count_objects;
+	files->base.find_abbrev_len = odb_source_files_find_abbrev_len;
 	files->base.freshen_object = odb_source_files_freshen_object;
 	files->base.write_object = odb_source_files_write_object;
 	files->base.write_object_stream = odb_source_files_write_object_stream;
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.