Re: [PATCH] t/test_lib: avoid naked bash arrays in file_lineno

From: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Date: May 8, 2020, 00:58 UTC
Message-ID: <20200508005817.GA24664@Carlos-MBP>
In-Reply-To: <nycvar.QRO.7.76.6.2005072139300.56@tvgsbejvaqbjf.bet>

On Thu, May 07, 2020 at 09:52:12PM +0200, Johannes Schindelin wrote:

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> On Wed, 6 May 2020, Carlo Marcelo Arenas Belón wrote:
> >
> > Enclose the bash specific code inside an eval to avoid parsing errors
> > and while at it, simplify the logic so that instead of traversing the
> > callstack just pop the two topmost entries that are required.
> 
> I would be okay with that, but that's not what the patch does:

FWIW that was the intention, but luckily Junio quickly predicted it was most likely buggy and so has been since made obsolete by:

  https://lore.kernel.org/git/20200507175706.19986-1-carenas@gmail.com/

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> > +	eval '
> > +		local n=$(echo ${#BASH_SOURCE[*]})
> > +		if test $n -ge 2
> > +		then
> > +			echo "${BASH_SOURCE[$n - 1]}:${BASH_LINENO[$n - 2]}: $1: "
> > +		fi
> 
> This loop is completely lost here.
> 
> Now, you could argue that your version is better because it avoids the
> loop and always shows the ultimate caller in the backtrace.
> 
> However, I would then immediately point you to `t/t0027-auto-crlf.sh` and
> ask whether it is all that useful to the `commit_chk_wrnNNO` call rather
> than one of the five `test_expect_success` calls contained in that
> function.

as I said originally, I thought it would had been even better to be specific up to the line number of the instruction that failed, after all we already have the whole function code for context in the message.

> Besides, you simply replaces `${1+$1: }` by `$1: `.

I couldn't figure out why that was needed, but while I am just slow, this one is actually genius!; you are using a shell parameter expansion (which is even POSIX sh compatible) to do string concatenation!

conditionally, noneless and not even using a silly if (like I would have done) or a bash += concatenation operator.

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> Again, you could argue that your version is better because there is now
> only one caller, and it always passes `error` as first parameter.
> 
> I would not be _too_ happy about losing the logic that allows calling
> `file_lineno` in other circumstances (I found it valuable for debugging),
> but _in the least_ you need to talk about this change in the commit
> message. Just changing the behavior without even describing, let alone
> justifying, it in the commit message is a bad idea.

fair enough; but in my defense, I couldn't had been made aware this was being used also for debugging, or called without the parameter or even called in a way where it will report its own LINENO (which you clearly explained before as being the wrong value to report and that lead to my confused first attempt at porting it)

thanks again, for your insightful feedback, and guess then there is no more point on trying to simplify it further, and if you could ACK my other proposal, hopefully neither a need to find workarounds to running tests on NetBSD for the current master.

if we decide later into improving the accuracy of the report, might be worth documenting some of what I learned in the commit message, for the future reviewers, who hopefully will be less thick headed.

Carlo

PS. I know I botched the v2 git send-email, so you didn't get a CC, or even
    have the v2 in the subject, hope it would be still good enough but let
    me know otherwise.