tests: do not let lazy prereqs inside `test_expect_*` turn off tracing

The `test_expect_*` functions use `test_eval_` and so does
`test_run_lazy_prereq_`. If tracing is enabled via the `-x` option,
`test_eval_` turns on tracing while evaluating the code block, and turns
it off directly after it.

This is unwanted for nested invocations.

One somewhat surprising example of this is when running a test that
calls `test_i18ngrep`: that function requires the `C_LOCALE_OUTPUT`
prereq, and that prereq is a lazy one, so it is evaluated via
`test_eval_`, the command tracing is turned off, and the test case
continues to run _without tracing the commands_.

Another somewhat surprising example is when one lazy prereq depends on
another lazy prereq: the former will call `test_have_prereq` with the
latter one, which in turn calls `test_eval_` and -- you guessed it --
tracing (if enabled) will be turned off _before_ returning to evaluating
the other lazy prereq.

As we will introduce just such a scenario with the GPG, GPGSM and
RFC1991 prereqs, let's fix that by introducing a variable that keeps
track of the current trace level: nested `test_eval_` calls will
increment and then decrement the level, and only when it reaches 0, the
tracing will _actually_ be turned off.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index 3e440c078d..b859721620 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -833,6 +833,19 @@ then
 	exit 1
 fi
 
+test_expect_success 'lazy prereqs do not turn off tracing' "
+	run_sub_test_lib_test lazy-prereq-and-tracing \
+		'lazy prereqs and -x' -v -x <<-\\EOF &&
+	test_lazy_prereq LAZY true
+
+	test_expect_success lazy 'test_have_prereq LAZY && echo trace'
+
+	test_done
+	EOF
+
+	grep 'echo trace' lazy-prereq-and-tracing/err
+"
+
 test_expect_success 'tests clean up even on failures' "
 	run_sub_test_lib_test_err \
 		failing-cleanup 'Failing tests with cleanup commands' <<-\\EOF &&