Re: Confusing error message in rebase when commit becomes empty

[Jeff King <peff@peff.net>]

On Wed, Jun 11, 2014 at 01:49:04PM +0100, Peter Krefting wrote:

> Hi!
> 
> I am rebasing a branch to combine a couple of commits. One is a revert of a
> previous commit. Since there are commits in-between, I do "squash" to make
> sure I get everything, and then add the actual change on top of that. The
> problem is that rebase stops with a confusing error message (from commit,
> presumably):
> 
>   $ git rebase --interactive
>   [...]
>   You asked to amend the most recent commit, but doing so would make
>   it empty. You can repeat your command with --allow-empty, or you can
>   remove the commit entirely with "git reset HEAD^".
>   rebase in progress; onto 342b22f
>   You are currently rebasing branch 'mybranch' on '342b22f'.
> 
>   No changes
> 
>   Could not apply 4682a1f20f6ac29546536921bc6ea0386441e23e... Revert "something"
> 
> OK, so I should retry the command with --allow-empty, then:
> 
>   $ git rebase --interactive --allow-empty
>   error: unknown option `allow-empty'
> 
> Nope, that's not quite right.

Yeah, that message comes from "commit --amend", which is called by
rebase to handle the squash. The "repeat your command" part is
confusing. The right thing to do here is:

  git commit --amend --allow-empty

if you want to have an empty commit, or:

  git reset HEAD^

if you want to have nothing.

Of course the first one would never occur to you, because it is not
"your command" in the first place. :)

We could change it to say "use git commit --amend --allow-empty", though
that is slightly incomplete for other cases (e.g., you might have
actually said "git commit --amend -a", and the right advice is to
include that "-a".

Commit understands a "whence" flag that could let it customize the
message for the case of rebase. But I think you would have to teach
determine_whence to figure out that we are in a rebase.

> Running "git rebase --continue" does work as expected, but perhaps it just
> shouldn't stop in this case?

As you noticed later in the thread, doing "--continue" omits the revert.
That's because it is telling rebase "OK, I've fixed this up, we can keep
going". But of course it wasn't fixed.