2 files changed, 38 insertions, 12 deletions

diff --git a/notes.c b/notes.c
index 4ee4fec233..3f4ae35340 100644
--- a/notes.c
+++ b/notes.c
@@ -340,15 +340,28 @@ static void load_subtree(struct leaf_node *subtree, struct int_node *node,
 	free(buf);
 }
 
-static void initialize_notes(const char *notes_ref_name)
+void init_notes(const char *notes_ref, int flags)
 {
 	unsigned char sha1[20], object_sha1[20];
 	unsigned mode;
 	struct leaf_node root_tree;
 
-	if (!notes_ref_name || read_ref(notes_ref_name, object_sha1) ||
-	    get_tree_entry(object_sha1, "", sha1, &mode))
+	assert(!initialized);
+	initialized = 1;
+
+	if (!notes_ref)
+		notes_ref = getenv(GIT_NOTES_REF_ENVIRONMENT);
+	if (!notes_ref)
+		notes_ref = notes_ref_name; /* value of core.notesRef config */
+	if (!notes_ref)
+		notes_ref = GIT_NOTES_DEFAULT_REF;
+
+	if (flags & NOTES_INIT_EMPTY || !notes_ref ||
+	    read_ref(notes_ref, object_sha1))
 		return;
+	if (get_tree_entry(object_sha1, "", sha1, &mode))
+		die("Failed to read notes tree referenced by %s (%s)",
+		    notes_ref, object_sha1);
 
 	hashclr(root_tree.key_sha1);
 	hashcpy(root_tree.val_sha1, sha1);
@@ -379,15 +392,8 @@ void format_note(const unsigned char *object_sha1, struct strbuf *sb,
 	unsigned long linelen, msglen;
 	enum object_type type;
 
-	if (!initialized) {
-		const char *env = getenv(GIT_NOTES_REF_ENVIRONMENT);
-		if (env)
-			notes_ref_name = getenv(GIT_NOTES_REF_ENVIRONMENT);
-		else if (!notes_ref_name)
-			notes_ref_name = GIT_NOTES_DEFAULT_REF;
-		initialize_notes(notes_ref_name);
-		initialized = 1;
-	}
+	if (!initialized)
+		init_notes(NULL, 0);
 
 	sha1 = lookup_notes(object_sha1);
 	if (!sha1)
diff --git a/notes.h b/notes.h
index d745ed12da..6b527991b0 100644
--- a/notes.h
+++ b/notes.h
@@ -1,6 +1,26 @@
 #ifndef NOTES_H
 #define NOTES_H
 
+/*
+ * Flags controlling behaviour of notes tree initialization
+ *
+ * Default behaviour is to initialize the notes tree from the tree object
+ * specified by the given (or default) notes ref.
+ */
+#define NOTES_INIT_EMPTY 1
+
+/*
+ * Initialize internal notes tree structure with the notes tree at the given
+ * ref. If given ref is NULL, the value of the $GIT_NOTES_REF environment
+ * variable is used, and if that is missing, the default notes ref is used
+ * ("refs/notes/commits").
+ *
+ * If you need to re-intialize the internal notes tree structure (e.g. loading
+ * from a different notes ref), please first de-initialize the current notes
+ * tree by calling free_notes().
+ */
+void init_notes(const char *notes_ref, int flags);
+
 /* Free (and de-initialize) the internal notes tree structure */
 void free_notes(void);