Subject: Re: [PATCH 2/2] builtin add -p: fix hunk splitting

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Mon, 20 Dec 2021 20:06:00 +0100

On Mon, Dec 20 2021, Phillip Wood via GitGitGadget wrote:

> From: Phillip Wood <[email-masked]>
>
> To determine whether a hunk can be split a counter is incremented each
> time a context line follows an insertion or deletion. If at the end of
> the hunk the value of this counter is greater than one then the hunk
> can be split into that number of smaller hunks. If the last hunk in a
> file ends with an insertion or deletion then there is no following
> context line and the counter will not be incremented. This case is
> already handled at the end of the loop where counter is incremented if
> the last hunk ended with an insertion or deletion. Unfortunately there
> is no similar check between files (likely because the perl version
> only ever parses one diff at a time). Fix this by checking if the last
> hunk ended with an insertion or deletion when we see the diff header
> of a new file and extend the existing regression test.
>
> Reproted-by: SZEDER Gábor <[email-masked]>
> Signed-off-by: Phillip Wood <[email-masked]>
> ---
>  add-patch.c                |  7 ++++++
>  t/t3701-add-interactive.sh | 46 ++++++++++++++++++++++++++++++++++----
>  2 files changed, 49 insertions(+), 4 deletions(-)
>
> diff --git a/add-patch.c b/add-patch.c
> index 8c41cdfe39b..5cea70666e9 100644
> --- a/add-patch.c
> +++ b/add-patch.c
> @@ -472,6 +472,13 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
>  			eol = pend;
>  
>  		if (starts_with(p, "diff ")) {
> +			if (marker == '-' || marker == '+')
> +				/*
> +				 * Last hunk ended in non-context line (i.e. it
> +				 * appended lines to the file, so there are no
> +				 * trailing context lines).
> +				 */
> +				hunk->splittable_into++;

I wondered if factoring out these several "marker == '-' || marker ==
'+'" cases in parse_diff() into a "is_plus_minus(marker)" was worth it,
but probably not.

>  			ALLOC_GROW_BY(s->file_diff, s->file_diff_nr, 1,
>  				   file_diff_alloc);
>  			file_diff = s->file_diff + s->file_diff_nr - 1;
> diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
> index 77de0029ba5..94537a6b40a 100755
> --- a/t/t3701-add-interactive.sh
> +++ b/t/t3701-add-interactive.sh
> @@ -326,7 +326,9 @@ test_expect_success 'correct message when there is nothing to do' '
>  test_expect_success 'setup again' '
>  	git reset --hard &&
>  	test_chmod +x file &&
> -	echo content >>file
> +	echo content >>file &&
> +	test_write_lines A B C D>file2 &&

style nit: "cmd args >file2" not "cmd args>file2"

> @@ -373,8 +411,8 @@ test_expect_success 'setup expected' '
>  test_expect_success 'add first line works' '
>  	git commit -am "clear local changes" &&
>  	git apply patch &&
> -	test_write_lines s y y | git add -p file 2>error >raw-output &&
> -	sed -n -e "s/^([1-2]\/[1-2]) Stage this hunk[^@]*\(@@ .*\)/\1/" \
> +	test_write_lines s y y s y n y | git add -p 2>error >raw-output &&
> +	sed -n -e "s/^([1-9]\/[1-9]) Stage this hunk[^@]*\(@@ .*\)/\1/" \
>  	       -e "/^[-+@ \\\\]"/p raw-output >output &&
>  	test_must_be_empty error &&
>  	git diff --cached >diff &&

style/diff nit: maybe worth it to in 1/2 do some version of:

    test_write_lines ... >lines &&
    git ... <lines .. &&
    ...
    sed -n \
    	-e ... \
        -e ... \
        >output

Just to make the diff smaller, i.e. just the "test_write_lines" line
would be modified here.

The changes themselves & this series LGTM.