Re: [PATCH v5 05/10] rebase: fix incompatiblity checks for --[no-]reapply-cherry-picks

> From: Elijah Newren <newren@gmail.com>
> 
> --[no-]reapply-cherry-picks was traditionally only supported by the
> sequencer.  Support was added for the apply backend, when --keep-base is
> also specified, in commit ce5238a690 ("rebase --keep-base: imply
> --reapply-cherry-picks", 2022-10-17).  Make the code error out when
> --[no-]reapply-cherry-picks is specified AND the apply backend is used
> AND --keep-base is not specified.  Also, clarify a number of comments
> surrounding the interaction of these flags.

> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>   Documentation/git-rebase.txt           |  2 +-
>   builtin/rebase.c                       | 34 ++++++++++++++++----------
>   t/t3422-rebase-incompatible-options.sh | 10 ++++++++
>   3 files changed, 32 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
> index 846aeed1b69..8a09f12d897 100644
> --- a/Documentation/git-rebase.txt
> +++ b/Documentation/git-rebase.txt
> @@ -650,7 +650,7 @@ are incompatible with the following options:
>    * --exec
>    * --no-keep-empty
>    * --empty=
> - * --reapply-cherry-picks
> + * --[no-]reapply-cherry-picks when used without --keep-base
>    * --edit-todo
>    * --update-refs
>    * --root when used without --onto
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index b742cc8fb5c..05b130bfae5 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -1224,13 +1224,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>   		if (options.fork_point < 0)
>   			options.fork_point = 0;
>   	}
> -	/*
> -	 * --keep-base defaults to --reapply-cherry-picks to avoid losing
> -	 * commits when using this option.
> -	 */
> -	if (options.reapply_cherry_picks < 0)
> -		options.reapply_cherry_picks = keep_base;
> -
>   	if (options.root && options.fork_point > 0)
>   		die(_("options '%s' and '%s' cannot be used together"), "--root", "--fork-point");
>   
> @@ -1406,12 +1399,27 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
>   	if (options.empty != EMPTY_UNSPECIFIED)
>   		imply_merge(&options, "--empty");
>   
> -	/*
> -	 * --keep-base implements --reapply-cherry-picks by altering upstream so
> -	 * it works with both backends.
> -	 */
> -	if (options.reapply_cherry_picks && !keep_base)
> -		imply_merge(&options, "--reapply-cherry-picks");
> +	if (options.reapply_cherry_picks < 0)
> +		/*
> +		 * We default to --no-reapply-cherry-picks unless
> +		 * --keep-base is given; when --keep-base is given, we want
> +		 * to default to --reapply-cherry-picks.
> +		 */
> +		options.reapply_cherry_picks = keep_base;
> +	else if (!keep_base)
> +		/*
> +		 * The apply backend always searches for and drops cherry
> +		 * picks.  This is often not wanted with --keep-base, so
> +		 * --keep-base allows --reapply-cherry-picks to be
> +		 * simulated by altering the upstream such that
> +		 * cherry-picks cannot be detected and thus all commits are
> +		 * reapplied.  Thus, --[no-]reapply-cherry-picks is
> +		 * supported when --keep-base is specified, but not when
> +		 * --keep-base is left out.
> +		 */
> +		imply_merge(&options, options.reapply_cherry_picks ?
> +					  "--reapply-cherry-picks" :
> +					  "--no-reapply-cherry-picks");
>   
>   	if (gpg_sign)
>   		options.gpg_sign_opt = xstrfmt("-S%s", gpg_sign);
> diff --git a/t/t3422-rebase-incompatible-options.sh b/t/t3422-rebase-incompatible-options.sh
> index f86274990b0..826f3b94ae6 100755
> --- a/t/t3422-rebase-incompatible-options.sh
> +++ b/t/t3422-rebase-incompatible-options.sh
> @@ -60,6 +60,16 @@ test_rebase_am_only () {
>   		test_must_fail git rebase $opt --exec 'true' A
>   	"
>   
> +	test_expect_success "$opt incompatible with --no-reapply-cherry-picks" "
> +		git checkout B^0 &&
> +		test_must_fail git rebase $opt --no-reapply-cherry-picks A
> +	"
> +
> +	test_expect_success "$opt incompatible with --reapply-cherry-picks" "
> +		git checkout B^0 &&
> +		test_must_fail git rebase $opt --reapply-cherry-picks A
> +	"
> +
>   	test_expect_success "$opt incompatible with --update-refs" "
>   		git checkout B^0 &&
>   		test_must_fail git rebase $opt --update-refs A