[PATCH] t5503: simplify setup of test which exercises failure of backfill

[PATCH] t5503: simplify setup of test which exercises failure of backfill

[Patrick Steinhardt]

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In the testcase to exercise backfilling of tags for fetches we evoke a
failure of the backfilling mechanism by creating a reference that later
on causes a D/F conflict. Because the assumption was that git-fetch(1)
would notice the D/F conflict early on this conflicting reference was
created via the reference-transaction hook just when we were about to
write the backfilled tag. As it turns out though this is not the case,
and the fetch fails in the same way when we create the conflicting ref
up front.

Simplify the test setup creating the reference up front, which allows us
to get rid of the hook script.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---

This simplifies the test setup of t5503 as discussed in [1]. The patch
applies on top of Junio's ps/fetch-atomic (583bc41923 (fetch: make
`--atomic` flag cover pruning of refs, 2022-02-17)).

Patrick

 t/t5503-tagfollow.sh | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/t/t5503-tagfollow.sh b/t/t5503-tagfollow.sh
index e72fdc2534..a3c01014b7 100755
--- a/t/t5503-tagfollow.sh
+++ b/t/t5503-tagfollow.sh
@@ -212,21 +212,11 @@ test_expect_success 'atomic fetch with backfill should use single transaction' '
 test_expect_success 'backfill failure causes command to fail' '
 	git init clone5 &&
 
-	write_script clone5/.git/hooks/reference-transaction <<-EOF &&
-		while read oldrev newrev reference
-		do
-			if test "\$reference" = refs/tags/tag1
-			then
-				# Create a nested tag below the actual tag we
-				# wanted to write, which causes a D/F conflict
-				# later when we want to commit refs/tags/tag1.
-				# We cannot just `exit 1` here given that this
-				# would cause us to die immediately.
-				git update-ref refs/tags/tag1/nested $B
-				exit \$!
-			fi
-		done
-	EOF
+	# Create a tag that is nested below the tag we are about to fetch via
+	# the backfill mechanism. This causes a D/F conflict when backfilling
+	# and should thus cause the command to fail.
+	empty_blob=$(git -C clone5 hash-object -w --stdin </dev/null) &&
+	git -C clone5 update-ref refs/tags/tag1/nested $empty_blob &&
 
 	test_must_fail git -C clone5 fetch .. $B:refs/heads/something &&
 	test $B = $(git -C clone5 rev-parse --verify refs/heads/something) &&
-- 
2.35.1


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Re: [PATCH] t5503: simplify setup of test which exercises failure of backfill

[Ævar Arnfjörð Bjarmason]

On Thu, Mar 03 2022, Patrick Steinhardt wrote:

> [[PGP Signed Part:Undecided]]
> In the testcase to exercise backfilling of tags for fetches we evoke a
> failure of the backfilling mechanism by creating a reference that later
> on causes a D/F conflict. Because the assumption was that git-fetch(1)
> would notice the D/F conflict early on this conflicting reference was
> created via the reference-transaction hook just when we were about to
> write the backfilled tag. As it turns out though this is not the case,
> and the fetch fails in the same way when we create the conflicting ref
> up front.
>
> Simplify the test setup creating the reference up front, which allows us
> to get rid of the hook script.
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>
> This simplifies the test setup of t5503 as discussed in [1]. The patch
> applies on top of Junio's ps/fetch-atomic (583bc41923 (fetch: make
> `--atomic` flag cover pruning of refs, 2022-02-17)).

FWIW for something in "next" already the OID will be stable, so it's OK
(and better) to mention 583bc419235 in the commit message itself.

> Patrick
>
>  t/t5503-tagfollow.sh | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
>
> diff --git a/t/t5503-tagfollow.sh b/t/t5503-tagfollow.sh
> index e72fdc2534..a3c01014b7 100755
> --- a/t/t5503-tagfollow.sh
> +++ b/t/t5503-tagfollow.sh
> @@ -212,21 +212,11 @@ test_expect_success 'atomic fetch with backfill should use single transaction' '
>  test_expect_success 'backfill failure causes command to fail' '
>  	git init clone5 &&
>  
> -	write_script clone5/.git/hooks/reference-transaction <<-EOF &&
> -		while read oldrev newrev reference
> -		do
> -			if test "\$reference" = refs/tags/tag1
> -			then
> -				# Create a nested tag below the actual tag we
> -				# wanted to write, which causes a D/F conflict
> -				# later when we want to commit refs/tags/tag1.
> -				# We cannot just `exit 1` here given that this
> -				# would cause us to die immediately.
> -				git update-ref refs/tags/tag1/nested $B
> -				exit \$!
> -			fi
> -		done
> -	EOF
> +	# Create a tag that is nested below the tag we are about to fetch via
> +	# the backfill mechanism. This causes a D/F conflict when backfilling
> +	# and should thus cause the command to fail.
> +	empty_blob=$(git -C clone5 hash-object -w --stdin </dev/null) &&
> +	git -C clone5 update-ref refs/tags/tag1/nested $empty_blob &&

This looks better, but FWIW for the discussion about quoted
v.s. unquoted here-doc in this case it's also OK for the pre-image (and
arguably better) to do (and any issues of $? v.s. $! etc. aside):
	
	diff --git a/t/t5503-tagfollow.sh b/t/t5503-tagfollow.sh
	index e72fdc25346..eebf0ddc4c2 100755
	--- a/t/t5503-tagfollow.sh
	+++ b/t/t5503-tagfollow.sh
	@@ -212,18 +212,18 @@ test_expect_success 'atomic fetch with backfill should use single transaction' '
	 test_expect_success 'backfill failure causes command to fail' '
	 	git init clone5 &&
	 
	-	write_script clone5/.git/hooks/reference-transaction <<-EOF &&
	+	write_script clone5/.git/hooks/reference-transaction <<-\EOF &&
	 		while read oldrev newrev reference
	 		do
	-			if test "\$reference" = refs/tags/tag1
	+			if test "$reference" = refs/tags/tag1
	 			then
	 				# Create a nested tag below the actual tag we
	 				# wanted to write, which causes a D/F conflict
	 				# later when we want to commit refs/tags/tag1.
	 				# We cannot just `exit 1` here given that this
	 				# would cause us to die immediately.
	-				git update-ref refs/tags/tag1/nested $B
	-				exit \$!
	+				git update-ref refs/tags/tag1/nested '$B'
	+				exit $!
	 			fi
	 		done
	 	EOF

I.e. to end the quote and interpolate $B. IMO also more readable as
e.g. shell syntax highlighting will show that we're interpolating that
outside-test $B.

>  
>  	test_must_fail git -C clone5 fetch .. $B:refs/heads/something &&
>  	test $B = $(git -C clone5 rev-parse --verify refs/heads/something) &&

(In the pre-image, but..) this way of using "test" will hide segfaults
etc. from the invoked git command.

Better to:

    echo $B >expect &&
    git ... >actual &&
    test_cmp expect actual

Or better yet "test_cmp_rev" in this case, but all of that's in "next"
already, so purely optional (and also more food for the "hiding exit
status" microproject) :)