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

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 27 Jan 2022 04:23:10 +0100

On Wed, Jan 26 2022, Josh Steadmon wrote:

> 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 <[email-masked]>
> Signed-off-by: Josh Steadmon <[email-masked]>
> ---
> 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.

I think it would be good to turn that -e into a -we, which would tell
you why this doesn't work the way you think:

    Possible attempt to put comments in qw() list at -e line 14.
    Possible attempt to separate words with commas at -e line 14.

I.e. you added one string "#" to the array, and a string "Allow" etc.

I think replacing it with this would be clearer, and means that...

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0f7a137c7d8..9a7611f412f 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 $ok = join("|", qw(
-		TRACE
+		TRACE(?!2_(?:PARENT_NAME|PARENT_SID)$)
 		DEBUG
 		TEST
 		.*_TEST

>  		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

...you won't need this hunk, since it'll be obvious that we're
specifically excluding those variables.

But more generally I think it's best to replace this with the below,
i.e. to also fold the nearby "unset" into this command which'll find
everything we need to unset for us, since it was doing most of the work
anyway.

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 0f7a137c7d8..ff4d4a553be 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -426,13 +426,12 @@ export LANG LC_ALL PAGER TZ COLUMNS
 EDITOR=:
 
 # A call to "unset" with no arguments causes at least Solaris 10
-# /usr/xpg4/bin/sh and /bin/ksh to bail out.  So keep the unsets
-# deriving from the command substitution clustered with the other
-# ones.
-unset VISUAL EMAIL LANGUAGE $("$PERL_PATH" -e '
+# /usr/xpg4/bin/sh and /bin/ksh to bail out.  So we'll need at least
+# one unconditional variable here, which might as well be VISUAL.
+unset VISUAL $("$PERL_PATH" -we '
 	my @env = keys %ENV;
 	my $ok = join("|", qw(
-		TRACE
+		TRACE(?!2_(?:PARENT_NAME|PARENT_SID)$)
 		DEBUG
 		TEST
 		.*_TEST
@@ -444,11 +443,20 @@ unset VISUAL EMAIL LANGUAGE $("$PERL_PATH" -e '
 		TRACE_CURL
 	));
 	my @vars = grep(/^GIT_/ && !/^GIT_($ok)/o, @env);
+	my @nongit = qw(
+		CDPATH
+		EMAIL
+		GITPERLLIB
+		GREP_OPTIONS
+		LANGUAGE
+		UNZIP
+		XDG_CACHE_HOME
+		XDG_CONFIG_HOME
+	);
+	push @vars => grep { exists $ENV{$_} } @nongit;
 	print join("\n", @vars);
 ')
-unset XDG_CACHE_HOME
-unset XDG_CONFIG_HOME
-unset GITPERLLIB
+
 TEST_AUTHOR_LOCALNAME=author
 TEST_AUTHOR_DOMAIN=example.com
 GIT_AUTHOR_EMAIL=${TEST_AUTHOR_LOCALNAME}@${TEST_AUTHOR_DOMAIN}
@@ -524,13 +532,6 @@ else
 	}
 fi
 
-# Protect ourselves from common misconfiguration to export
-# CDPATH into the environment
-unset CDPATH
-
-unset GREP_OPTIONS
-unset UNZIP
-
 case $(echo $GIT_TRACE |tr "[A-Z]" "[a-z]") in
 1|2|true)
 	GIT_TRACE=4