tests: replace chainlint subshell with a function

To test that we don't break the &&-chain, test-lib.sh does something
like:

   (exit 117) && $test_commands

and checks that the result is exit code 117. We don't care what that
initial command is, as long as it exits with a unique code. Using "exit"
works and is simple, but is a bit expensive since it requires a subshell
(to avoid exiting the whole script!). This isn't usually very
noticeable, but it can add up for scripts which have a large number of
tests.

Using "return" naively won't work here, because we'd return from the
function eval-ing the snippet (and it wouldn't find &&-chain breakages).
But if we further push that into its own function, it does exactly what
we want, without extra subshell overhead.

According to hyperfine, this produces a measurable improvement when
running t3070 (which has 1800 tests, all of them quite short):

  'HEAD' ran
    1.09 ± 0.01 times faster than 'HEAD~1'

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 097895663747fed84e31fe57495e478dad026065..cfcbd899c5a4bd136f9976dfccda92e8fda76639 100644 (file)
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1086,6 +1086,10 @@ test_eval_ () {
        return $test_eval_ret_
 }
 
+fail_117 () {
+       return 117
+}
+
 test_run_ () {
        test_cleanup=:
        expecting_failure=$2
@@ -1097,7 +1101,7 @@ test_run_ () {
                trace=
                # 117 is magic because it is unlikely to match the exit
                # code of other programs
-               if test "OK-117" != "$(test_eval_ "(exit 117) && $1${LF}${LF}echo OK-\$?" 3>&1)"
+               if test "OK-117" != "$(test_eval_ "fail_117 && $1${LF}${LF}echo OK-\$?" 3>&1)"
                then
                        BUG "broken &&-chain or run-away HERE-DOC: $1"
                fi