From: Phillip Wood <phillip.wood@dunelm.org.uk>

The only todo commands that accept a merge commit are "merge" and
"reset". All the other commands like "pick" or "reword" fail when they
try to pick a a merge commit and print the message

    error: commit abc123 is a merge but no -m option was given.

followed by a hint about the command being rescheduled. This message is
designed to help the user when they cherry-pick a merge and forget to
pass "-m". For users who are rebasing the message is confusing as there
is no way for rebase to cherry-pick the merge.

Improve the user experience by detecting the error when the todo list is
parsed rather than waiting for the "pick" command to fail and print a
message recommending the "merge" command instead. We recommend "merge"
rather than "exec git cherry-pick -m ..." on the assumption that
cherry-picking merges is relatively rare and it is more likely that the
user chose "pick" by a mistake.

It would be possible to support cherry-picking merges by allowing the
user to pass "-m" to "pick" commands but that adds complexity to do
something that can already be achieved with

    exec git cherry-pick -m1 abc123

The change is relatively straight forward but is complicated slightly as
we now need to tell the parser if we're rebasing or not.

Reported-by: Stefan Haller <lists@haller-berlin.de>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>

Submitted-As: https://lore.kernel.org/git/pull.1672.git.1708945087691.gitgitgadget@gmail.com