[PATCH] maintenance tests: fix systemd v2.34.0-rc* test regression

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Fix tests added in b681b191f92 (maintenance: add support for systemd
timers on Linux, 2021-09-04) to run successfully no systems where
systemd-analyze is installed, but on which there's a discrepancy
between a FILE argument of "/lib/systemd/system/basic.target" and
"systemd/user/git-maintenance@.service" succeeding.

There was an attempt to work around previous breakage in these tests
in 670e5973992 (maintenance: fix test t7900-maintenance.sh,
2021-09-27), as noted in my [1] that commit is wrong about its
assumption that we can use "/lib/systemd/system/basic.target" as a
canary.argument.

To fix this let's adjust this test to test what it really should be
testing: If we've got systemd-analyze reporting anything useful, we
should use it to check the syntax of our just-generated
"systemd/user/git-maintenance@.service" file.

Even on systems where this previously succeeded we weren't effectively
doing that, because "systemd-analyze" will pass various syntax errors
by and exit with a status code of 0, e.g. if the "[Unit]" section is
replaced with a nonsensical "[HlaghUnfUnf]" section.

To do that ignore whatever exit code we get from "systemd-analyze
verify", and filter its stderr output to extract the sorts of lines it
emits no note syntax warnings and errors. We need to filter out
"Failed to load", which would be emitted e.g. on the
gcc135.fsffrance.org test box[1].

We also need to pipe this output to FD's 5 & 6, to avoid mixing up the
trace output with our own output under "-x".

1. https://lore.kernel.org/git/211026.8635oo11jk.gmgdl@evledraar.gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---

Junio: I think you'll want this in v2.34.0 per the report in
<211026.8635oo11jk.gmgdl@evledraar.gmail.com>.

 t/t7900-maintenance.sh | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 74aa6384755..5fe2ea03c1d 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -20,15 +20,16 @@ test_xmllint () {
 	fi
 }
 
-test_lazy_prereq SYSTEMD_ANALYZE '
-	systemd-analyze verify /lib/systemd/system/basic.target
-'
-
 test_systemd_analyze_verify () {
-	if test_have_prereq SYSTEMD_ANALYZE
-	then
-		systemd-analyze verify "$@"
-	fi
+	# Ignoring any errors from systemd-analyze is intentional
+	systemd-analyze verify "$@" >systemd.out 2>systemd.err;
+
+	cat systemd.out >&5 &&
+	sed -n \
+		-e '/^Failed to load/d' \
+		-e '/git-maintenance@i*\.service:/x' \
+		<systemd.err >&6 &&
+	rm systemd.out systemd.err
 }
 
 test_expect_success 'help text' '
@@ -697,7 +698,11 @@ test_expect_success 'start and stop Linux/systemd maintenance' '
 	# start registers the repo
 	git config --get --global --fixed-value maintenance.repo "$(pwd)" &&
 
-	test_systemd_analyze_verify "systemd/user/git-maintenance@.service" &&
+	# If we have a systemd-analyze on the system we can verify the
+	# generated file.
+	test_systemd_analyze_verify "systemd/user/git-maintenance@.service" 5>out 6>err &&
+	test_must_be_empty out &&
+	test_must_be_empty err &&
 
 	printf -- "--user enable --now git-maintenance@%s.timer\n" hourly daily weekly >expect &&
 	test_cmp expect args &&
-- 
2.33.1.1570.g069344fdd45