Subject: Re: [PATCH 2/7] merge-ort: maintain expected invariant for priv member

From: Taylor Blau <[email-masked]>
Date: Thu, 13 Jun 2024 18:59:02 -0400

On Thu, Jun 13, 2024 at 08:25:02PM +0000, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <[email-masked]>
>
> The calling convention for the merge machinery is
>    One call to          init_merge_options()
>    One or more calls to merge_incore_[non]recursive()
>    One call to          merge_finalize()
>       (possibly indirectly via merge_switch_to_result())
> Both merge_switch_to_result() and merge_finalize() expect
>    opt->priv == NULL && result->priv != NULL
> which is supposed to be set up by our move_opt_priv_to_result_priv()
> function.  However, two codepath dealing with error cases did not

s/codepath/&s/ ?

> execute this necessary logic, which could result in assertion failures
> (or, if assertions were compiled out, could result in segfaults).  Fix
> the oversight and add a test that would have caught one of these
> problems.
>
> While at it, also tighten an existing test for a non-recursive merge
> to verify that it fails correctly, i.e. with the expected exit code
> rather than with an assertion failure.

I suspect that this test was flaky, too, since if the assertion errors
were compiled out and it died via a segfault, the test would have failed
outright as test_must_fail does not allow for segfaults typically.

So I'm glad to see us tightening up that area of the test suite.

> Reported-by: Matt Cree <[email-masked]>
> Signed-off-by: Elijah Newren <[email-masked]>
> ---
>  merge-ort.c           |  3 ++-
>  t/t6406-merge-attr.sh | 42 +++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/merge-ort.c b/merge-ort.c
> index 10f5a655f29..6ca7b0f9be4 100644
> --- a/merge-ort.c
> +++ b/merge-ort.c
> @@ -5015,7 +5015,7 @@ static void move_opt_priv_to_result_priv(struct merge_options *opt,
>  	 * to move it.
>  	 */
>  	assert(opt->priv && !result->priv);
> -	if (!opt->priv->call_depth) {
> +	if (!opt->priv->call_depth || result->clean < 0) {
>  		result->priv = opt->priv;
>  		result->_properly_initialized = RESULT_INITIALIZED;
>  		opt->priv = NULL;
> @@ -5052,6 +5052,7 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
>  		    oid_to_hex(&side1->object.oid),
>  		    oid_to_hex(&side2->object.oid));
>  		result->clean = -1;
> +		move_opt_priv_to_result_priv(opt, result);
>  		return;
>  	}
>  	trace2_region_leave("merge", "collect_merge_info", opt->repo);
> diff --git a/t/t6406-merge-attr.sh b/t/t6406-merge-attr.sh
> index 156a1efacfe..b6db5c2cc36 100755
> --- a/t/t6406-merge-attr.sh
> +++ b/t/t6406-merge-attr.sh
> @@ -185,7 +185,7 @@ test_expect_success !WINDOWS 'custom merge driver that is killed with a signal'
>
>  	>./please-abort &&
>  	echo "* merge=custom" >.gitattributes &&
> -	test_must_fail git merge main 2>err &&
> +	test_expect_code 2 git merge main 2>err &&
>  	grep "^error: failed to execute internal merge" err &&
>  	git ls-files -u >output &&
>  	git diff --name-only HEAD >>output &&
> @@ -261,4 +261,44 @@ test_expect_success 'binary files with union attribute' '
>  	grep -i "warning.*cannot merge.*HEAD vs. bin-main" output
>  '
>
> +test_expect_success !WINDOWS 'custom merge driver that is killed with a signal on recursive merge' '
> +	test_when_finished "rm -f output please-abort" &&
> +	test_when_finished "git checkout side" &&
> +
> +	git reset --hard anchor &&
> +
> +	git checkout -b base-a main^ &&
> +	echo base-a >text &&
> +	git commit -m base-a text &&
> +
> +	git checkout -b base-b main^ &&
> +	echo base-b >text &&
> +	git commit -m base-b text &&
> +
> +	git checkout -b recursive-a base-a &&
> +	test_must_fail git merge base-b &&

Here and below, do you care about the particular exit code of merging as
above? IOW, should these be `test_expect_code`'s as well?

Thanks,
Taylor