[PATCH v2] test-lib: unset trace2 parent envvars

[Josh Steadmon <steadmon@google.com>]

The trace2 subsystem can inherit certain information from parent
processes via environment variables; e.g., the parent command name and
session ID. This allows trace2 to note when a command is the child
process of another Git process, and to adjust various pieces of output
accordingly.

This behavior breaks certain tests that examine trace2 output when the
tests run as a child of another git process, such as in `git rebase -x
"make test"`.

While we could fix this by unsetting the relevant variables in the
affected tests (currently t0210, t0211, t0212, and t6421), this would
leave other tests vulnerable to similar breakage if new test cases are
added which inspect trace2 output.

In t/test-lib.sh, we keep a pattern of permitted GIT_* environment
variables. Variables matching /^GIT_TRACE.*/ are currently allowed via
this pattern. We want to preserve this behavior, because it can be
useful to collect trace output over the entire test suite. Instead of
modifying the allow-pattern, we instead fix this issue by unsetting only
the GIT_TRACE2_PARENT_NAME and GIT_TRACE2_PARENT_SID in t/test-lib.sh.

Reported-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Josh Steadmon <steadmon@google.com>
---
Updated commit message and added code comments to explain why we keep
"TRACE" in the allow pattern.

 t/test-lib.sh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0f7a137c7d..faf25ba1b2 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -432,7 +432,7 @@ EDITOR=:
 unset VISUAL EMAIL LANGUAGE $("$PERL_PATH" -e '
 	my @env = keys %ENV;
 	my $ok = join("|", qw(
-		TRACE
+		TRACE	# Allow tracing in general, but see unsets below.
 		DEBUG
 		TEST
 		.*_TEST
@@ -449,6 +449,10 @@ unset VISUAL EMAIL LANGUAGE $("$PERL_PATH" -e '
 unset XDG_CACHE_HOME
 unset XDG_CONFIG_HOME
 unset GITPERLLIB
+# Unset trace environment variables that can interfere with trace output used in
+# certain tests.
+unset GIT_TRACE2_PARENT_NAME
+unset GIT_TRACE2_PARENT_SID
 TEST_AUTHOR_LOCALNAME=author
 TEST_AUTHOR_DOMAIN=example.com
 GIT_AUTHOR_EMAIL=${TEST_AUTHOR_LOCALNAME}@${TEST_AUTHOR_DOMAIN}

base-commit: dcc0cd074f0c639a0df20461a301af6d45bd582e
-- 
2.35.0.rc0.227.g00780c9af4-goog