object-file: hide internals when we need to reprepare loose sources

There are two different situations where we have to clear the cache of
loose objects:

  - When freeing the loose object source itself to avoid memory leaks.

  - When repreparing the loose object source so that any potentially-
    stale data is getting evicted from the cache.

The former is already handled by `odb_source_loose_free()`. But the
latter case is still done manually by in `odb_reprepare()`, so we are
leaking internals into that code.

Introduce a new `odb_source_loose_reprepare()` function as an equivalent
to `packfile_store_prepare()` to hide these implementation details.
Furthermore, while at it, rename the function `odb_clear_loose_cache()`
to `odb_source_loose_clear()`.

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

Author: pks-t

object-file.c

@@ -1834,12 +1834,17 @@ struct oidtree *odb_source_loose_cache(struct odb_source *source,
 	return source->loose->cache;
 }
 
-void odb_clear_loose_cache(struct odb_source *source)
+static void odb_source_loose_clear_cache(struct odb_source_loose *loose)
 {
-	oidtree_clear(source->loose->cache);
-	FREE_AND_NULL(source->loose->cache);
-	memset(&source->loose->subdir_seen, 0,
-	       sizeof(source->loose->subdir_seen));
+	oidtree_clear(loose->cache);
+	FREE_AND_NULL(loose->cache);
+	memset(&loose->subdir_seen, 0,
+	       sizeof(loose->subdir_seen));
+}
+
+void odb_source_loose_reprepare(struct odb_source *source)
+{
+	odb_source_loose_clear_cache(source->loose);
 }
 
 static int check_stream_oid(git_zstream *stream,
@@ -2008,6 +2013,6 @@ void odb_source_loose_free(struct odb_source_loose *loose)
 {
 	if (!loose)
 		return;
-	odb_clear_loose_cache(loose->source);
+	odb_source_loose_clear_cache(loose);
 	free(loose);
 }

object-file.h

@@ -37,16 +37,16 @@ struct odb_source_loose {
 struct odb_source_loose *odb_source_loose_new(struct odb_source *source);
 void odb_source_loose_free(struct odb_source_loose *loose);
 
+/* Reprepare the loose source by emptying the loose object cache. */
+void odb_source_loose_reprepare(struct odb_source *source);
+
 /*
  * Populate and return the loose object cache array corresponding to the
  * given object ID.
  */
 struct oidtree *odb_source_loose_cache(struct odb_source *source,
 				       const struct object_id *oid);
 
-/* Empty the loose object cache for the specified object directory. */
-void odb_clear_loose_cache(struct odb_source *source);
-
 /*
  * Put in `buf` the name of the file in the local object database that
  * would be used to store a loose object with the specified oid.

odb.c

@@ -1071,7 +1071,7 @@ void odb_reprepare(struct object_database *o)
 	odb_prepare_alternates(o);
 
 	for (source = o->sources; source; source = source->next)
-		odb_clear_loose_cache(source);
+		odb_source_loose_reprepare(source);
 
 	o->approximate_object_count_valid = 0;