Subject: Re: [PATCH v2] parallel-checkout: avoid dash local bug in tests

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Sat, 05 Jun 2021 21:56:05 +0200

On Sat, Jun 05 2021, René Scharfe wrote:

> 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
>
> That's because wc's output contains leading spaces and this version of
> dash erroneously expands the variable declaration as "local workers= 0",
> i.e. it tries to set the "workers" variable to the empty string and also
> declare a variable named "0", which not a valid name.  This is a known
> dash bug (https://bugs.launchpad.net/ubuntu/+source/dash/+bug/139097).
>
> Work around it by passing the command output directly to test instead of
> storing it in a variable first.  While at it, let grep count the number
> of lines instead of piping its output to wc, which is a bit shorter and
> more efficient.
>
> Helped-by: Matheus Tavares Bernardino <[email-masked]>
> Signed-off-by: René Scharfe <[email-masked]>
> ---
> Changes since v1:
> - Explain the root cause.
> - Get rid of the local variable "workers".
> - Adjust title accordingly.
> - Still use grep -c, though.
> - Remove input redirection.
>
>  t/lib-parallel-checkout.sh | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/t/lib-parallel-checkout.sh b/t/lib-parallel-checkout.sh
> index 21f5759732..66350d5207 100644
> --- a/t/lib-parallel-checkout.sh
> +++ b/t/lib-parallel-checkout.sh
> @@ -27,8 +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) &&
> -	test $workers -eq $expected_workers &&
> +	test $(grep -c "child_start\[..*\] git checkout--worker" "$trace_file") -eq $expected_workers &&
>  	rm "$trace_file"
>  } 8>&2 2>&4

I'd find this thing much clearer if the v2 just narrowly focused on
avoiding the "local", and thus demonstrated the non-portable shell
issue, and perhaps with something like:
	
	diff --git a/t/check-non-portable-shell.pl b/t/check-non-portable-shell.pl
	index fd3303552be..aad6f3e2bf1 100755
	--- a/t/check-non-portable-shell.pl
	+++ b/t/check-non-portable-shell.pl
	@@ -48,6 +48,7 @@ sub err {
	 	/\bexport\s+[A-Za-z0-9_]*=/ and err '"export FOO=bar" is not portable (use FOO=bar && export FOO)';
	 	/^\s*([A-Z0-9_]+=(\w*|(["']).*?\3)\s+)+(\w+)/ and exists($func{$4}) and
	 		err '"FOO=bar shell_func" assignment extends beyond "shell_func"';
	+	/\blocal\b \S+=\$\(.*?\|\s*\bwc -l\)/ and err 'whitespace handling in local=$(... | wc -l) differs in some dash versions';
	 	$line = '';
	 	# this resets our $. for each file
	 	close ARGV if eof;

The let's do grep -c while we're at it part of this IMO just adds
confusion while skimming future portability issues with --grep=dash or
--grep=POSIX in the future, and looking at the history in v1 it's just
there because in v1 the root cause wasn't fully understood.

If we're doing a general cleanup of that pattern it would seem to be
better to search-replace this with the rest of them in another commit:

    $ git grep '\$\(grep.*\| wc -l' -- t | wc -l
    27