[PATCH 0/2] replay: die descriptively when invalid commit-ish

From: Kristoffer Haugsbakk <code@khaugsbakk.name>

You get this error when you for example mistype the argument to `--onto`:

    fatal: Replaying down to root commit is not supported yet!

Consider that you might not know yourself that you have mistyped something; then this looks even more puzzling. You might have given a range like `main..topic` but the command says that it would need to replay down to the root commit.

The only thing that’s happened though is that `NULL` has been interpreted in the wrong way.

Let’s instead die immediately when the real error happens, in other words when we can’t find the commit for the given commit-ish.

Also add more regression tests.

Somewhat unrelated to this change—and caveat not a C programmer—I was confused by `determine_replay_mode`. Most of the function deals with three cases:

    if (onto_name) {
    ...
    } else if (*advance_name) {
    ...
    } else {
    ...
    }

But I don’t get the `else` since you now need to provide either `--onto` or `--advance`. And both require an argument. So when can the fallthrough `else` happen?

I thought that maybe the `else` was old code that predated `--onto` and `--advance` being mandatory. But that whole method and this check was added in the same commit, in 22d99f01 (replay: add --advance or 'cherry-pick' mode, 2023-11-24):

    if (!onto_name && !advance_name) {
            error(_("option --onto or --advance is mandatory"));

But just ignore this section if I’m simply confused.

Kristoffer Haugsbakk (2):
  replay: die descriptively when invalid commit-ish
  t3650: add more regression tests for failure conditions

 builtin/replay.c         |  2 +-
 t/t3650-replay-basics.sh | 43 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)

base-commit: 9a2fb147f2c61d0cab52c883e7e26f5b7948e3ed