Re: [PATCH v2 2/2] rebase: mark --update-refs as requiring the merge backend

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Elijah

Thanks for working on this

On 20/01/2023 04:56, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@gmail.com>
> 
> --update-refs is built in terms of the sequencer, which requires the
> merge backend.  It was already marked as incompatible with the apply
> backend in the git-rebase manual, but the code didn't check for this
> incompatibility and warn the user.  Check and warn now.

Strictly speaking we die rather than warn but I don't think that 
warrants a re-roll. I just had a quick look to see how easy it would be 
to add the advice Stolee's patch had if the user has set 
rebase.updaterefs but does not pass "--no-update-refs" when using the 
apply backend but it looks a bit fiddly unfortunately as we could die in 
imply_merge() or later on.

Thinking more generally, imply_merge() does a good job of telling the 
user which option is incompatible with "--apply" but if the user passes 
a merge option with "--whitespace=fix" and omits "--apply" then we just 
print a generic message saying "apply options and merge options cannot 
be used together" which isn't terribly helpful to the user (doubly so 
when the merge option come from a config setting).

I've also noticed that "--autosquash" is ignored if we end up using the 
apply backend. That's a separate issue but shares the "this may have 
come from a config setting rather than a command line argument" problem.

All in all I'm not sure if it is friendlier to die when the user has 
rebsase.updaterefs set and they try to rebase with "--whitespace=fix" or 
if it is better just to ignore the config in that case. If we can find a 
way to print some help when we die in that case it would be nicer for 
the user.

Best Wishes

Phillip

> While at it, fix a typo in t3422...and fix some misleading wording (all
> useful options other than --whitespace=fix have long since been
> implemented in the merge backend).
> 
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>   builtin/rebase.c                       |  3 +++
>   t/t3422-rebase-incompatible-options.sh | 15 ++++++++++-----
>   2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index ace8bd4a41c..e8bcdbf9fcd 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -1507,6 +1507,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>   		}
>   	}
>   
> +	if (options.update_refs)
> +		imply_merge(&options, "--update-refs");
> +
>   	if (options.type == REBASE_UNSPECIFIED) {
>   		if (!strcmp(options.default_backend, "merge"))
>   			imply_merge(&options, "--merge");
> diff --git a/t/t3422-rebase-incompatible-options.sh b/t/t3422-rebase-incompatible-options.sh
> index ebcbd79ab8a..d72c863b21b 100755
> --- a/t/t3422-rebase-incompatible-options.sh
> +++ b/t/t3422-rebase-incompatible-options.sh
> @@ -25,11 +25,11 @@ test_expect_success 'setup' '
>   '
>   
>   #
> -# Rebase has lots of useful options like --whitepsace=fix, which are
> -# actually all built in terms of flags to git-am.  Since neither
> -# --merge nor --interactive (nor any options that imply those two) use
> -# git-am, using them together will result in flags like --whitespace=fix
> -# being ignored.  Make sure rebase warns the user and aborts instead.
> +# Rebase has a useful option, --whitespace=fix, which is actually
> +# built in terms of flags to git-am.  Since neither --merge nor
> +# --interactive (nor any options that imply those two) use git-am,
> +# using them together will result in --whitespace=fix being ignored.
> +# Make sure rebase warns the user and aborts instead.
>   #
>   
>   test_rebase_am_only () {
> @@ -60,6 +60,11 @@ test_rebase_am_only () {
>   		test_must_fail git rebase $opt --exec 'true' A
>   	"
>   
> +	test_expect_success "$opt incompatible with --update-refs" "
> +		git checkout B^0 &&
> +		test_must_fail git rebase $opt --update-refs A
> +	"
> +
>   }
>   
>   test_rebase_am_only --whitespace=fix