[PATCH] parallel-checkout: use grep -c to count workers in tests

The parallel checkout tests fail when run with /bin/dash on MacOS 11.4,
reporting the following error:

   ./t2080-parallel-checkout-basics.sh: 33: local: 0: bad variable name

This seems to be caused by a bug in dash, which doesn't like the pipe
into wc for some reason.  We can work around it and make the test
slightly shorter and faster by having grep do the counting, though, so
let's do that.

Signed-off-by: René Scharfe <redacted>
---
Reduced test case for underlying dash issue:

   $ dash -c 'foo () { local bar=$(echo baz | wc); }; foo'
   dash: 1: local: 1: bad variable name


The pipe is not even required to trigger the issue:

   $ dash -c 'foo () { local bar=$(wc /dev/null); }; foo'
   dash: 1: local: 0: bad variable name

Turning wc into a function calms the shell:

   $ dash -c 'foo () { local bar=$(echo baz | wc); }; wc () { :; }; foo'

Setting a global variable also works fine:

   $ dash -c 'foo () { bar=$(echo baz | wc); }; foo'

 t/lib-parallel-checkout.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/t/lib-parallel-checkout.sh b/t/lib-parallel-checkout.sh
index 21f5759732..145276eb4c 100644
--- a/t/lib-parallel-checkout.sh
+++ b/t/lib-parallel-checkout.sh

@@ -27,7 +27,7 @@ test_checkout_workers () {
 	rm -f "$trace_file" &&
 	GIT_TRACE2="$(pwd)/$trace_file" "$@" 2>&8 &&

-	local workers=$(grep "child_start\[..*\] git checkout--worker" "$trace_file" | wc -l) &&
+	local workers=$(grep -c "child_start\[..*\] git checkout--worker" <"$trace_file") &&
 	test $workers -eq $expected_workers &&
 	rm "$trace_file"
 } 8>&2 2>&4
--

2.31.1