Re: [PATCHv6 06/23] notes.h/c: Propagate combine_notes_fn return value to add_note() and beyond

The combine_notes_fn functions uses a non-zero return value to indicate
failure. However, this return value was converted to a call to die()
in note_tree_insert().

Instead, propagate this return value out to add_note(), and return it
from there to enable the caller to handle errors appropriately.

Existing add_note() callers are updated to die() upon failure, thus
preserving the current behaviour. The only exceptions are copy_note()
and notes_cache_put() where we are able to propagate the add_note()
return value instead.

This patch has been improved by the following contributions:
- Jonathan Nieder: Future-proof by always checking add_note() return value
- Jonathan Nieder: Improve clarity of final if-condition in note_tree_insert()

Thanks-to: Jonathan Nieder [off-list ref]
Signed-off-by: Johan Herland <redacted>
---
 builtin/notes.c |   11 ++++++-----
 notes-cache.c   |    3 +--
 notes.c         |   55 ++++++++++++++++++++++++++++---------------------------
 notes.h         |   11 ++++++++---
 4 files changed, 43 insertions(+), 37 deletions(-)

diff --git a/builtin/notes.c b/builtin/notes.c
index fbc347c..35f6eb6 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c

@@ -573,8 +573,8 @@ static int add(int argc, const char **argv, const char *prefix)

       if (is_null_sha1(new_note))
               remove_note(t, object);
-       else
-               add_note(t, object, new_note, combine_notes_overwrite);
+       else if (add_note(t, object, new_note, combine_notes_overwrite))
+               die("confused: combine_notes_overwrite failed");