Subject: Re: [PATCH v4 0/3] test-lib.sh: have all tests pass under "-x", remove BASH_XTRACEFD

From: SZEDER Gábor <[email-masked]>
Date: Mon, 13 Dec 2021 06:43:53 +0100

On Mon, Dec 13, 2021 at 02:38:33AM +0100, Ævar Arnfjörð Bjarmason wrote:
> A re-arrangement-only change to v3[1]. The previous 2/2 is now split
> into two commits, as requested by SZEDER[2] in the removal of
> BASH_XTRACEFD is now its own commit & the rationale for doing so is
> outlined in detail.

I'm afraid I wasn't clear.  What I meant was that if we were to remove
BASH_XTRACEFD, then it should be done its own commit.

But again: BASH_XTRACEFD is the only simple yet reliable and robust
way to get -x trace from our tests, so do not remove it.

> 1. https://lore.kernel.org/git/[email-masked]/
> 2. https://lore.kernel.org/git/[email-masked]/
> 
> Ævar Arnfjörð Bjarmason (3):
>   t1510: remove need for "test_untraceable", retain coverage
>   test-lib.sh: remove the now-unused "test_untraceable" facility
>   test-lib.sh: remove "BASH_XTRACEFD"
> 
>  t/README              |  3 --
>  t/t1510-repo-setup.sh | 85 +++++++++++++++++++++----------------------
>  t/test-lib.sh         | 66 ++++-----------------------------
>  3 files changed, 49 insertions(+), 105 deletions(-)
> 
> Range-diff against v3:
> 1:  7876202c5b0 = 1:  9e7b089dc50 t1510: remove need for "test_untraceable", retain coverage
> -:  ----------- > 2:  60883fd95cb test-lib.sh: remove the now-unused "test_untraceable" facility
> 2:  a7fc794e20d ! 3:  8b5ae33376e test-lib.sh: remove the now-unused "test_untraceable" facility
>     @@ Metadata
>      Author: Ævar Arnfjörð Bjarmason <[email-masked]>
>      
>       ## Commit message ##
>     -    test-lib.sh: remove the now-unused "test_untraceable" facility
>     +    test-lib.sh: remove "BASH_XTRACEFD"
>      
>     -    In the preceding commit the use of "test_untraceable=UnfortunatelyYes"
>     -    was removed from "t1510-repo-setup.sh" in favor of more narrow
>     -    redirections of the output of specific commands (and not entire
>     -    sub-shells or functions).
>     +    Stop setting "BASH_XTRACEFD=4" to direct "-x" output to file
>     +    descriptor 4 under bash.
>      
>     -    This is in line with the fixes in the series that introduced the
>     -    "test_untraceable" facility. See 571e472dc43 (Merge branch
>     -    'sg/test-x', 2018-03-14) for the series as a whole, and
>     -    e.g. 91538d0cde9 (t5570-git-daemon: don't check the stderr of a
>     -    subshell, 2018-02-24) for a commit that's in line with the changes in
>     -    the preceding commit.
>     +    When it was added in d88785e424a (test-lib: set BASH_XTRACEFD
>     +    automatically, 2016-05-11) it was needed as a workaround for various
>     +    tests that didn't pass cleanly under "-x".
>      
>     -    We've thus solved the TODO item noted when "test_untraceable" was
>     -    added to "t1510-repo-setup.sh" in 58275069288 (t1510-repo-setup: mark
>     -    as untraceable with '-x', 2018-02-24).
>     +    Most of those were later fixed in 71e472dc43 (Merge branch
>     +    'sg/test-x', 2018-03-14), and in the preceding commits we've fixed the
>     +    final remaining and removed the "test_untraceable" facility.
>      
>     -    So let's remove the feature entirely. Not only is it currently unused,
>     -    but it actively encourages an anti-pattern in our tests. We should be
>     -    testing the output of specific commands, not entire subshells or
>     -    functions.
>     +    The reason we don't need this anymore is becomes clear from reading
>     +    the rationale in d88785e424a and applying those arguments to the
>     +    current state of the codebase. In particular it said (with "this" and
>     +    "it" referring to the problem of tests failing under "-x"):
>      
>     -    That the "-x" output had to be disabled as a result is only one
>     -    symptom, but even under bash those tests will be harder to debug as
>     -    the subsequent check of the redirected file will be far removed from
>     -    the command that emitted the output.
>     +        "there here isn't a portable or scalable solution to this [...] we
>     +        can work around it by pointing the "set -x" output to our
>     +        descriptor 4"
>      
>     -    Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
>     +    And finally that:
>      
>     - ## t/README ##
>     -@@ t/README: appropriately before running "make". Short options can be bundled, i.e.
>     - -x::
>     - 	Turn on shell tracing (i.e., `set -x`) during the tests
>     - 	themselves. Implies `--verbose`.
>     --	Ignored in test scripts that set the variable 'test_untraceable'
>     --	to a non-empty value, unless it's run with a Bash version
>     --	supporting BASH_XTRACEFD, i.e. v4.1 or later.
>     - 
>     - -d::
>     - --debug::
>     +        "Automatic tests for our "-x" option may be a bit too meta"
>     +
>     +    Those tests are exactly what we've had since aedffe95250 (travis-ci:
>     +    run tests with '-x' tracing, 2018-02-24), so punting on fixing issues
>     +    with "-x" by using "BASH_XTRACEFD=4" isn't needed anymore, we're now
>     +    committing to maintaining the test suite in a way that won't break
>     +    under "-x".
>     +
>     +    We could retain "BASH_XTRACEFD=4" anyway, but doing so is bad because:
>     +
>     +     1) Since we're caring about "-x" passing in CI under "dash" on Ubuntu
>     +        using "BASH_XTRACEFD=4" will amount to hiding an error we'll run
>     +        into eventually. Tests will pass locally with "bash", but fail in
>     +        CI with "dash" (or under other non-"bash" shells).
>     +
>     +     2) As the amended code in "test_eval_" shows (an amended revert to
>     +        the pre-image of d88785e424a) it's simpler to not have to take
>     +        this "bash" special-case into account.
>     +
>     +    Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
>      
>       ## t/test-lib.sh ##
>     -@@ t/test-lib.sh: then
>     - 	exit
>     - fi
>     - 
>     --if test -n "$trace" && test -n "$test_untraceable"
>     --then
>     --	# '-x' tracing requested, but this test script can't be reliably
>     --	# traced, unless it is run with a Bash version supporting
>     --	# BASH_XTRACEFD (introduced in Bash v4.1).
>     --	#
>     --	# Perform this version check _after_ the test script was
>     --	# potentially re-executed with $TEST_SHELL_PATH for '--tee' or
>     --	# '--verbose-log', so the right shell is checked and the
>     --	# warning is issued only once.
>     --	if test -n "$BASH_VERSION" && eval '
>     --	     test ${BASH_VERSINFO[0]} -gt 4 || {
>     --	       test ${BASH_VERSINFO[0]} -eq 4 &&
>     --	       test ${BASH_VERSINFO[1]} -ge 1
>     --	     }
>     --	   '
>     --	then
>     --		: Executed by a Bash version supporting BASH_XTRACEFD.  Good.
>     --	else
>     --		echo >&2 "warning: ignoring -x; '$0' is untraceable without BASH_XTRACEFD"
>     --		trace=
>     --	fi
>     --fi
>     - if test -n "$trace" && test -z "$verbose_log"
>     - then
>     - 	verbose=t
>      @@ t/test-lib.sh: else
>       	exec 4>/dev/null 3>/dev/null
>       fi
> -- 
> 2.34.1.1024.g573f2f4b767
>