Re: [PATCH] notes: Disallow reusing non-blob as a note object

Currently "git notes add -C $object" will read the raw bytes from $object,
and then copy those bytes into the note object, which is hardcoded to be
of type blob. This means that if the given $object is a non-blob (e.g.
tree or commit), the raw bytes from that object is copied into a blob
object. This is probably not useful, and certainly not what any sane
user would expect. So disallow it, by erroring out if the $object passed
to the -C option is not a blob.

The fix also applies to the -c option (in which the user is prompted to
edit/verify the note contents in a text editor), and also when -c/-C is
passed to "git notes append" (which appends the $object contents to an
existing note object). In both cases, passing a non-blob $object does not
make sense.

Also add a couple of tests demonstrating expected behavior.

Suggested-by: Junio C Hamano <redacted>
Signed-off-by: Johan Herland <redacted>
---
 builtin/notes.c  |  6 +++++-
 t/t3301-notes.sh | 27 +++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/builtin/notes.c b/builtin/notes.c
index 2b24d05..bb89930 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c

@@ -269,7 +269,11 @@ static int parse_reuse_arg(const struct option *opt, const char *arg, int unset)
                die(_("Failed to resolve '%s' as a valid ref."), arg);
        if (!(buf = read_sha1_file(object, &type, &len)) || !len) {
                free(buf);
-               die(_("Failed to read object '%s'."), arg);;
+               die(_("Failed to read object '%s'."), arg);
+       }
+       if (type != OBJ_BLOB) {
+               free(buf);
+               die(_("Cannot read note data from non-blob object '%s'."), arg);