Junio C Hamano [off-list ref] writes:

quoted

+static char *separator = "\n";

The only two ways this pointer gains a non-NULL value are with this
initialization and parsing the command line "--separator=<value>"
option with OPT_STRING().  Neither of them allocate new storage but
points an existing string that we do not "own" (and cannot free)
with the pointer.  So it probably is safer to make it a pointer to a
const string, i.e.

static const char *separator = "\n";

quoted

@@ -213,65 +229,96 @@ static void write_note_data(struct note_data *d, struct object_id *oid)
 	}
 }
 
+static void insert_separator(struct strbuf *message, size_t pos)
+{
+	if (separator[strlen(separator) - 1] == '\n')
+		strbuf_addstr(message, separator);
+	else
+		strbuf_insertf(message, pos, "%s%s", separator, "\n");
+}
+
+static void concat_messages(struct note_data *d)
+{
+	struct strbuf msg = STRBUF_INIT;
+
+	size_t i;
+	for (i = 0; i < d->msg_nr ; i++) {

Wrong placement of the blank line that separates the declaration and
the first statement.

Thanks for your advice and detailed explanation. I have noticed
in "what's cooking in git" that this patchset is being planed to
merge into 'next', so I display the diff here for the convenience
of applying, or please let me know if a new patch is required.

diff --git a/builtin/notes.c b/builtin/notes.c
index 8905298b..6eede305 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c

@@ -28,7 +28,7 @@
 #include "worktree.h"
 #include "write-or-die.h"
 
-static const char *separator = "\n";
+static char *separator = "\n";
 static const char * const git_notes_usage[] = {
        N_("git notes [--ref <notes-ref>] [list [<object>]]"),
        N_("git notes [--ref <notes-ref>] add [-f] [--allow-empty] [--separator=<paragraph-break>] [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]"),

@@ -248,8 +248,8 @@ static void append_separator(struct strbuf *message)
 static void concat_messages(struct note_data *d)
 {
        struct strbuf msg = STRBUF_INIT;
-       size_t i;
 
+       size_t i;
        for (i = 0; i < d->msg_nr ; i++) {
                if (d->buf.len)
                        append_separator(&d->buf);