alternates: provide helper for adding to alternates list

The submodule code wants to temporarily add an alternate
object store to our in-memory alt_odb list, but does it
manually. Let's provide a helper so it can reuse the code in
link_alt_odb_entry().

While we're adding our new add_to_alternates_memory(), let's
document add_to_alternates_file(), as the two are related.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/sha1_file.c b/sha1_file.c
index 3d8c1e8..7a3b745 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -440,6 +440,17 @@ void add_to_alternates_file(const char *reference)
 	free(alts);
 }
 
+void add_to_alternates_memory(const char *reference)
+{
+	/*
+	 * Make sure alternates are initialized, or else our entry may be
+	 * overwritten when they are.
+	 */
+	prepare_alt_odb();
+
+	link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+}
+
 /*
  * Compute the exact path an alternate is at and returns it. In case of
  * error NULL is returned and the human readable error is added to `err`