[PATCH] t4216: fix no-op test that breaks TAP output

[PATCH] t4216: fix no-op test that breaks TAP output

[Patrick Steinhardt]

In t4216 we have have a prerequisite that is active in case the system's
`char` type is signed by default. This prerequisite isn't really used by
anything though: while it is used to guard one of our tests, that
specific test is essentially a no-op. So all this infrastructure does is
to provide some debugging hint to a reader that pays a lot of attention.

Besides that, the way we set up the prerequisite also results in broken
TAP output on systems where `char` is unsigned by default: we use
`test_cmp()` to diff two files outside of of any test body, and if the
files differ we enable the prerequisite. If so, the call to `test_cmp()`
would also print output, and that output is of course not valid TAP
output.

That wasn't a problem before 389c83025d (t: let prove fail when parsing
invalid TAP output, 2026-06-04), because our TAP parser was configured
to be lenient. But starting with that commit, t4216 is now failing on
systems with unsigned chars.

Drop the whole infrastructure. The prerequisite is not used anywhere
else, and the only location where it's used doesn't really provide much
value.

Reported-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
Hi,

as reported in [1]. Thanks!

Patrick

<20260617220330.n6byiFQr@teonanacatl.net>
---
 t/t4216-log-bloom.sh | 21 ---------------------
 1 file changed, 21 deletions(-)

diff --git a/t/t4216-log-bloom.sh b/t/t4216-log-bloom.sh
index 1064990de3..16bc39c359 100755
--- a/t/t4216-log-bloom.sh
+++ b/t/t4216-log-bloom.sh
@@ -569,27 +569,6 @@ test_expect_success 'set up repo with high bit path, version 1 changed-path' '
 	git -C highbit1 commit-graph write --reachable --changed-paths
 '
 
-test_expect_success 'setup check value of version 1 changed-path' '
-	(
-		cd highbit1 &&
-		echo "52a9" >expect &&
-		get_first_changed_path_filter >actual
-	)
-'
-
-# expect will not match actual if char is unsigned by default. Write the test
-# in this way, so that a user running this test script can still see if the two
-# files match. (It will appear as an ordinary success if they match, and a skip
-# if not.)
-if test_cmp highbit1/expect highbit1/actual
-then
-	test_set_prereq SIGNED_CHAR_BY_DEFAULT
-fi
-test_expect_success SIGNED_CHAR_BY_DEFAULT 'check value of version 1 changed-path' '
-	# Only the prereq matters for this test.
-	true
-'
-
 test_expect_success 'setup make another commit' '
 	# "git log" does not use Bloom filters for root commits - see how, in
 	# revision.c, rev_compare_tree() (the only code path that eventually calls

---
base-commit: 95e20213faefeb95df29277c58ac1980ab68f701
change-id: 20260619-pks-t4216-drop-unused-prereq-5793107a0249

Re: [PATCH] t4216: fix no-op test that breaks TAP output

[Taylor Blau]

Hi Patrick,

A couple of thanks are owed: one to Todd for reporting this issue in the
first place, another to Peff for analyizing why it didn't appear broken
before, and a third for you for proposing a patch to fix it.

If you choose to delete this piece of test infrastructure entirely (I
think that there is an alternative direction that I would prefer, but
see below for more on why), I think the patch you wrote below is OK.

But...

On Fri, Jun 19, 2026 at 09:20:20AM +0200, Patrick Steinhardt wrote:
> In t4216 we have have a prerequisite that is active in case the system's
> `char` type is signed by default. This prerequisite isn't really used by
> anything though: while it is used to guard one of our tests, that
> specific test is essentially a no-op. So all this infrastructure does is
> to provide some debugging hint to a reader that pays a lot of attention.

I don't think that this is guarding nothing, but I agree that the test
as written is strange. As I recall, this was to sanity check the v1
Bloom values, but allow failures on platforms where the `char` type is
unsigned by default.

I don't feel that strongly about whether or not we check the exact
value of the filter, but I think there are a couple of arguments in
favor of doing so. Most compelling would be that we know that our
murmur3 implementation is correct (in at least one case) and that we
don't regress that case in the future. We do have these checks for v2
changed-path Bloom filters where the signed-ness of `char` is
irrelevant.

> Besides that, the way we set up the prerequisite also results in broken
> TAP output on systems where `char` is unsigned by default: we use
> `test_cmp()` to diff two files outside of of any test body, and if the
> files differ we enable the prerequisite. If so, the call to `test_cmp()`
> would also print output, and that output is of course not valid TAP
> output.

Given this and the above, I would probably err on the side of
designating this as 'test_lazy_prereq' or otherwise silencing the output
of 'test_cmp' so that this does not taint the TAP output.

Thanks,
Taylor

Re: [PATCH] t4216: fix no-op test that breaks TAP output

[Junio C Hamano]

Taylor Blau <me@ttaylorr.com> writes:

> Given this and the above, I would probably err on the side of
> designating this as 'test_lazy_prereq' or otherwise silencing the output
> of 'test_cmp' so that this does not taint the TAP output.

We can argue the merit and demerit with a good log message.  The
central issue at hand is how precious 52a9 in the script lost by
this patch is (in other words, are we checking more than "is our
char signed or unsigned?").

By the way, I do not quite get the _BY_DEFAULT in the name
SIGNED_CHAR_BY_DEFAULT.  The builder may have configured to use
signed char on a platform that can handle both and their char is by
default unsigned, and under such a condition, we would set this
prerequisite, even though the default on such a platform is
unsigned, no?