test-lib: add a GIT_TEST_PASSING_SANITIZE_LEAK=check mode

Add a new "GIT_TEST_PASSING_SANITIZE_LEAK=check" mode to the
test-lib.sh.

As noted in the updated "t/README" this compliments the existing
"GIT_TEST_PASSING_SANITIZE_LEAK=true" mode added in
956d2e4639 (tests: add a test mode for SANITIZE=leak, run it in CI,
2021-09-23).

Rather than document this all in one (even more) dense paragraph split
up the discussion of how it combines with --immediate into its own
paragraph following the discussion of
"GIT_TEST_SANITIZE_LEAK_LOG=true".

Before the removal of "test_external" in a preceding commit we would
have had to special-case t9700-perl-git.sh and t0202-gettext-perl.sh.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/README

@@ -371,11 +371,28 @@ declared themselves as leak-free by setting
 "TEST_PASSES_SANITIZE_LEAK=true" before sourcing "test-lib.sh". This
 test mode is used by the "linux-leaks" CI target.
 
+GIT_TEST_PASSING_SANITIZE_LEAK=check checks that our
+"TEST_PASSES_SANITIZE_LEAK=true" markings are current. Rather than
+skipping those tests that haven't set "TEST_PASSES_SANITIZE_LEAK=true"
+before sourcing "test-lib.sh" this mode runs them with
+"--invert-exit-code". This is used to check that there's a one-to-one
+mapping between "TEST_PASSES_SANITIZE_LEAK=true" and those tests that
+pass under "SANITIZE=leak". This is especially useful when testing a
+series that fixes various memory leaks with "git rebase -x".
+
 GIT_TEST_SANITIZE_LEAK_LOG=true will log memory leaks to
 "test-results/$TEST_NAME.leak/trace.*" files. The logs include a
 "dedup_token" (see +"ASAN_OPTIONS=help=1 ./git") and other options to
 make logs +machine-readable.
 
+GIT_TEST_PASSING_SANITIZE_LEAK=check when combined with "--immediate"
+will run to completion faster, and result in the same failing
+tests. The only practical reason to run
+GIT_TEST_PASSING_SANITIZE_LEAK=check without "--immediate" is to
+combine it with "GIT_TEST_SANITIZE_LEAK_LOG=true". If we stop at the
+first failing test case our leak logs won't show subsequent leaks we
+might have run into.
+
 GIT_TEST_PROTOCOL_VERSION=<n>, when set, makes 'protocol.version'
 default to n.
 

t/test-lib.sh

@@ -1451,18 +1451,35 @@ BAIL_OUT_ENV_NEEDS_SANITIZE_LEAK () {
 
 if test -n "$SANITIZE_LEAK"
 then
-	if test_bool_env GIT_TEST_PASSING_SANITIZE_LEAK false
+	# Normalize with test_bool_env
-	then
+	passes_sanitize_leak=
-		# We need to see it in "git env--helper" (via
-		# test_bool_env)
-		export TEST_PASSES_SANITIZE_LEAK
 
-		if ! test_bool_env TEST_PASSES_SANITIZE_LEAK false
+	# We need to see TEST_PASSES_SANITIZE_LEAK in "git
+	# env--helper" (via test_bool_env)
+	export TEST_PASSES_SANITIZE_LEAK
+	if test_bool_env TEST_PASSES_SANITIZE_LEAK false
+	then
+		passes_sanitize_leak=t
+	fi
+
+	if test "$GIT_TEST_PASSING_SANITIZE_LEAK" = "check"
+	then
+		if test -n "$invert_exit_code"
+		then
+			BAIL_OUT "cannot use --invert-exit-code under GIT_TEST_PASSING_SANITIZE_LEAK=check"
+		fi
+
+		if test -z "$passes_sanitize_leak"
+		then
+			say "in GIT_TEST_PASSING_SANITIZE_LEAK=check mode, setting --invert-exit-code for TEST_PASSES_SANITIZE_LEAK != true"
+			invert_exit_code=t
+		fi
+	elif test -z "$passes_sanitize_leak" &&
+	     test_bool_env GIT_TEST_PASSING_SANITIZE_LEAK false
 	then
 		skip_all="skipping $this_test under GIT_TEST_PASSING_SANITIZE_LEAK=true"
 		test_done
 	fi
-	fi
 
 	if test_bool_env GIT_TEST_SANITIZE_LEAK_LOG false
 	then
@@ -1480,7 +1497,8 @@ then
 		prepend_var LSAN_OPTIONS : log_path=\"$TEST_RESULTS_SAN_FILE\"
 		export LSAN_OPTIONS
 	fi
-elif test_bool_env GIT_TEST_PASSING_SANITIZE_LEAK false
+elif test "$GIT_TEST_PASSING_SANITIZE_LEAK" = "check" ||
+     test_bool_env GIT_TEST_PASSING_SANITIZE_LEAK false
 then
 	BAIL_OUT_ENV_NEEDS_SANITIZE_LEAK "GIT_TEST_PASSING_SANITIZE_LEAK=true"
 elif test_bool_env GIT_TEST_SANITIZE_LEAK_LOG false