On Sun, Aug 9, 2020 at 3:12 PM Junio C Hamano <gitster@xxxxxxxxx> wrote:
> The motivation makes quite a lot of sense.
>
> I suspect that it is a bug to use "-", i.e. "read from the standard
> input", for "$2", because
>
> (1) if it is used for the expected output, we got the comparison in
> the wrong direction;
I had the same concern that it didn't necessarily make sense to allow
"-" for $2, but eventually thought of a case such as:
sed '...' actual | test_cmp expect - &&
which massages 'actual' before test_cmp() sees it. True, we don't
actually have such callers, but it theoretically is legitimate.
> (2) if it is used for the actual output, we have a command whose
> output we are interested in on the upstream side of a pipe to
> discard its exit status.
If the command upstream is a Git command, that could indeed be a
reason for concern, but, as illustrated above, it could just be a
system command.
