[PATCH] tests: prefer host Git to verify chainlint self-checks

[Patrick Steinhardt <ps@pks.im>]

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The "check-chainlint" target runs automatically when running tests and
performs self-checks to verify that the chainlinter itself produces the
expected output. Originally, the chainlinter was implemented via sed,
but the infrastructure has been rewritten in fb41727b7e (t: retire
unused chainlint.sed, 2022-09-01) to use a Perl script instead.

The rewrite caused some slight whitespace changes in the output that are
ultimately not of much importance. In order to be able to assert that
the actual chainlinter errors match our expectations we thus have to
ignore whitespace characters when diffing them. As the `-w` flag is not
in POSIX we try to use `git diff -w --no-index` before we fall back to
`diff -w -u`.

To accomodate for cases where the host system has no Git installation we
use the locally-compiled version of Git. This can result in problems
though when the Git project's repository is using extensions that the
locally-compiled version of Git doesn't understand. It will refuse to
run and thus cause the checks to fail.

Fix this issue by prefering the host's Git resolved via PATH. If it
doesn't exist, then we fall back to the locally-compiled Git version and
diff as before.

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

I've started to dogfood the reftable backend on my local machine and
have converted many repositories to use the reftable backend. This
surfaced the described issue because the repository now sets up the
"extensions.refStorage" extension, and thus "check-chainlint" fails
depending on which versions of Git I'm trying to compile and test.

 t/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/t/Makefile b/t/Makefile
index 225aaf78ed..8b7f7aceaa 100644
--- a/t/Makefile
+++ b/t/Makefile
@@ -111,7 +111,9 @@ check-chainlint:
 	if test -f ../GIT-BUILD-OPTIONS; then \
 		. ../GIT-BUILD-OPTIONS; \
 	fi && \
-	if test -x ../git$$X; then \
+	if command -v git >/dev/null 2>&1; then \
+		DIFFW="git --no-pager diff -w --no-index"; \
+	elif test -x ../git$$X; then \
 		DIFFW="../git$$X --no-pager diff -w --no-index"; \
 	else \
 		DIFFW="diff -w -u"; \
-- 
2.43.GIT


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