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

> Hi Ævar
>
> On 20/12/2021 19:06, Ævar Arnfjörð Bjarmason wrote:
>> On Mon, Dec 20 2021, Phillip Wood via GitGitGadget wrote:
>> 
>>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>>
>>> 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 <szeder.dev@gmail.com>
>>> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>>> ---
>>>   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.
>
> Yeah in the end I just factored out this hunk into a new function but
> I didn't add a function for "marker == '-' || marker ==
>> '+'"
>
>>>   			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.
>
> In the end I decided to leave this as is, while refactoring slightly
> simplifies this patch it makes the previous one bigger and means that 
> would need to be reviewed again.

>> The changes themselves & this series LGTM.
>
> Thanks
>
> Best Wishes
>
> Phillip