This partially reverts 6c627fb30d "cli: default to log when no subcommand is
provided." We could reject an empty alias at all, but we would still need to
ensure that the expanded alias contained a subcommand name.
The help output is a bit odd as the <COMMAND> can be omitted, but I think
that's acceptable. If we do care about that, maybe we can override_usage().
This is basically the same as Mercurial's workaround. I don't know about Git,
but arguments order is very restricted in git, so -C path can be parsed prior
to alias expansion. In hg and jj, doing that would be messy and unreliable.
Closes#2414
This is a naive implementation, which cannot deal with multiple children
or parents stemming from merges.
Note: I gave each command separate a separate argument struct
for extensibility.
Fixes#878
I've extracted the `builtin_log_root` template for users to customize the
default templates without fully overriding them, for example I would remove
the change_id/commit_id for myself - and we discussed in Discord that leaving
those makes sense for the user to be reminded/teached that the root commit has
a change id made from z's.
