On Wed, Sep 15, 2021 at 4:22 AM Phillip Wood <phillip.wood123@xxxxxxxxx> wrote:
>
> On 15/09/2021 11:25, Phillip Wood wrote:
> > I do wonder (though a brief try failed to trigger it) if there are cases
> > where the diff algorithm does something "clever" which means it does not
> > treat a common prefix or suffix as unchanged (see d2f82950a9
> > ("Re(-re)*fix trim_common_tail()", 2007-12-20) for a related issue). We
> > could just trim the common prefix and suffix from the two sides
> > ourselves using xdl_recmatch().
>
> Here is an evil test case that shows this problem (diff on top of your patch)
>
>
> diff --git a/t/t6427-diff3-conflict-markers.sh b/t/t6427-diff3-conflict-markers.sh
> index de9c6190b9..836843c6b0 100755
> --- a/t/t6427-diff3-conflict-markers.sh
> +++ b/t/t6427-diff3-conflict-markers.sh
> @@ -219,8 +219,9 @@ test_setup_zdiff3 () {
> test_write_lines 1 2 3 4 5 6 7 8 9 >basic &&
> test_write_lines 1 2 3 AA 4 5 BB 6 7 8 >middle-common &&
> test_write_lines 1 2 3 4 5 6 7 8 9 >interesting &&
> + test_write_lines 1 2 3 4 5 6 7 8 9 >evil &&
>
> - git add basic middle-common &&
> + git add basic middle-common interesting evil &&
> git commit -m base &&
>
> git branch left &&
> @@ -230,19 +231,21 @@ test_setup_zdiff3 () {
> test_write_lines 1 2 3 4 A B C D E 7 8 9 >basic &&
> test_write_lines 1 2 3 CC 4 5 DD 6 7 8 >middle-common &&
> test_write_lines 1 2 3 4 A B C D E F G H I J 7 8 9 >interesting &&
> + test_write_lines 1 2 3 4 X A B C 7 8 9 >evil &&
> git add -u &&
> git commit -m letters &&
>
> git checkout right &&
> test_write_lines 1 2 3 4 A X C Y E 7 8 9 >basic &&
> test_write_lines 1 2 3 EE 4 5 FF 6 7 8 >middle-common &&
> test_write_lines 1 2 3 4 A B C 5 6 G H I J 7 8 9 >interesting &&
> + test_write_lines 1 2 3 4 Y A B C B C 7 8 9 >evil &&
> git add -u &&
> git commit -m permuted
> )
> }
>
> -test_expect_failure 'check zdiff3 markers' '
> +test_expect_success 'check zdiff3 markers' '
...except your new testcase makes it fail.
> test_setup_zdiff3 &&
> (
> cd zdiff3 &&
> @@ -251,6 +254,14 @@ test_expect_failure 'check zdiff3 markers' '
>
> test_must_fail git -c merge.conflictstyle=zdiff3 merge -s recursive right^0 &&
>
> + test_write_lines \
> + 1 2 3 4 \
> + "<<<<<<< HEAD" X A \
> + "||||||| $(git rev-parse --short HEAD^1)" 5 6 ======= \
> + Y A B C ">>>>>>> right^0" \
> + B C 7 8 9 >expect &&
> + test_cmp expect evil &&
> +
Yeah, this is an interesting testcase, and I agree with the 'expect'
choice you wrote, but the current code doesn't produce it. I'll
update the patches and send out another round, and then do you want to
try your xdl_recmatch() magic to fix this testcase?
