Re: [PATCH 1/2] replay: fail gracefully when a merge input is unreadable

[Junio C Hamano <gitster@pobox.com>]

"Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Elijah Newren <newren@gmail.com>
>
> When objects involved in the merge cannot be read, the merge machinery
> will return early with result.clean = -1, and result.tree left as NULL.
> pick_regular_commit() tested only "if (!result->clean)", ignoring the
> case where "clean < 0".  That causes the code to try to use
> result->tree, resulting in a SIGSEGV.
>
> Handle clean < 0 explicitly; the merge machinery will already have printed
> messages such as "Could not read <object>" and "collecting merge info
> failed for trees...", so we don't need to add much detail beyond the
> fact that the merge failed.
>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  replay.c                 |  7 +++++++
>  t/t3650-replay-basics.sh | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
>
> diff --git a/replay.c b/replay.c
> index 463c900d6c..33e21b2032 100644
> --- a/replay.c
> +++ b/replay.c
> @@ -327,6 +327,13 @@ static struct commit *pick_regular_commit(struct repository *repo,
>  	merge_opt->ancestor = NULL;
>  	merge_opt->branch2 = NULL;
>  
> +	if (result->clean < 0) {
> +		error(_("merge of %s onto %s failed"),
> +		      oid_to_hex(&pickme->object.oid),
> +		      oid_to_hex(&replayed_base->object.oid));
> +		return NULL;
> +	}
> +
>  	if (!result->clean)
>  		return NULL;

Hmph, so anything but "0 < result->clean" is a failure, but we by
mistake took any non-zero value as OK?  That is an obvious mistake.
Well spotted and fixed.

> +		# Ensure replay gracefully handles the missing object
> +		test_must_fail git replay --onto onto base..side 2>err &&
> +		test_grep ! "[Ss]egmentation" err &&
> +		test_grep "Could not read\|collecting merge info failed" err

"test_must_fail" means "the tested command must fail voluntarily and
in a controlled way", so a segfaulting git-replay invocation would
not pass test_must_fail.  Hence, there is no need to separately
test "test_grep ! '[sS]egmentation'".

Besides, the spelling used by strsignal() is implementation-defined,
so you cannot reliably grep for it anyway.

> +	)
> +'
> +
>  test_done

Thanks.