Re: [PATCH v3 2/2] test-lib.sh: remove the now-unused "test_untraceable" facility

On Mon, Dec 13, 2021 at 10:51:14AM -0800, Junio C Hamano wrote:

quoted

I don't see any argument pertinent to BASH_XTRACEFD in general in that
email, of in favor of its removal in particular, and there are no
valid arguments for its removal in earlier emails in this thread
either.

If I am reading Ævar right, the argument is "dash would not be fixed
with BASH_XTRACEFD, so there needs another way that would work there,
and if the approach happens to work also for bash, then there is no
reason to use BASH_XTRACEFD", I think.

Now, if the way Ævar came up with to help shells with "-x" not to
contaminate their standard error stream that our test scripts want
to inspect is worse to write, understand, and maintain, compared to
the way we have been writing our tests that inspect their standard
errors, without having to worry about "-x" output thanks to the use
of BASH_XTRACEFD, it may make a regression to developer
productivity, but I am not sure if that is the case.

I think the method for handling this in the test scripts _is_ worse to
write, understand, and maintain. The problem to me is less that it's
ugly to workaround (which as you note in this case is not great, but not
_too_ bad), but that it's a subtle friction point that may jump up and
bite any test-writer who does something like:

  (foo && bar) 2>stderr

So my view had always been that BASH_XTRACEFD is the good solution, and
if people want to make "-x" work reliably under other shells, then I
won't stop them. But somewhere along the way Gábor did a bunch of fixes
to get things mostly running, and the use of dash with "-x" got added to
CI, so now it's a de facto requirement (if you care about CI
complaining, which we increasingly do).

Maybe that's OK. We've had fewer incidences of the problem popping up
than I would have expected.

My vision was that we'd leave BASH_XTRACEFD so people using it could
remain oblivious if they chose, but if the ship has sailed via CI, then
that might have less value.

I think [1/2] of this same series can serve an example of how tests
must be tweaked to live under the world order without BASH_XTRACEFD?
Having to set and use a temporary file to capture the standard error
output and append to it upfront looks uglier than each individual
test locally capturing the standard error output from a single
invocation of a helper function, but it does not look _too_ bad to
me.  Can we find another example to argue for BASH_XTRACEFD, how
much it makes it easier to write tests that work even under "-x"?

I think the fixes from 571e472dc4 (Merge branch 'sg/test-x', 2018-03-14)
show what had to be done to get where we are today.

-Peff