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Re: policy around 'wontfix' bug tag




On Tue, Feb 06, 2018 at 01:48:19PM +0100, Vincent Lefevre wrote:
> On 2018-02-05 09:39:12 -0500, Greg Wooledge wrote:
> > Anyway, here's what I came up with:
> > 
> > lastday() {
> >     date +%Y-%m-%d -d "$1 1 day ago + 1 month"
> > }
> 
> But the exact meaning of "month" seems undocumented, which may
> silently break in a future version (e.g. possibly as a consequence
> of a bug fix). So this is a good example of what you should *not*
> do.

If I have the luxury of writing in a real language, then I prefer
to use that language's date/time libraries, if they exist and don't
suck.

In bash, you get this, or you get to write your own date/time code
by hand.

> This is completely crazy:

> Where is the logic behind that?

As noted by someone else earlier in this thread, date recently learned
a --debug option (this is my first time hearing about it), so let's
try that:

wooledg:~$ date --debug +%Y-%m-%d -d '2003-09-01 1 day ago + 1 month'
date: parsed date part: (Y-M-D) 2003-09-01
date: parsed relative part: -1 day(s)
date: parsed relative part: +1 month(s) -1 day(s)
date: input timezone: -05:00 (set from system default)
date: warning: using midnight as starting time: 00:00:00
date: starting date/time: '(Y-M-D) 2003-09-01 00:00:00 TZ=-05:00'
date: warning: when adding relative months/years, it is recommended to specify the 15th of the months
date: warning: when adding relative days, it is recommended to specify 12:00pm
date: after date adjustment (+0 years, +1 months, -1 days),
date:     new date/time = '(Y-M-D) 2003-09-30 00:00:00 TZ=-05:00'
date: '(Y-M-D) 2003-09-30 00:00:00 TZ=-05:00' = 1064894400 epoch-seconds
date: output timezone: -05:00 (set from system default)
date: final: 1064894400.000000000 (epoch-seconds)
date: final: (Y-M-D) 2003-09-30 04:00:00 (UTC0)
date: final: (Y-M-D) 2003-09-30 00:00:00 (output timezone TZ=-05:00)
2003-09-30

So, it adds "a month" first, then subtracts "a day" second.  I suppose
I could have rearranged the sub-arguments to make that clearer, but
honestly, I stopped tweaking it once I had a working invocation.  It's
so fragile that I didn't want to change *anything* for fear of breaking
it.

In some cases, I dealt with this stuff using a truly ancient version
of GNU date from the sh-utils package, before coreutils existed.  Some
of the more modern invocations didn't work with the older program, so
I often had to find different tricks that would work.  I don't know
whether this was one such case.  It could have been.