Re: [RFC][PATCH v4 06/11] Provide backward compatibility for strftime family (bug 10871).

[Rical Jasan <ricaljasan at pacific dot net>]

On 11/14/2016 05:38 PM, Rafal Luzynski wrote:
> Thank you, Rical for your feedback.  It's valuable even if I don't
> agree.  I'm sorry if I'm repeating the same thing again

I should apologize because I was not nearly as up on this bug as I
thought I was.  Thank you for the links; following the gnome/glib bug
which referenced the glibc bug 10871 as "glibc developers are not
interested in solving this on their level" had me paying closer
attention to the history there (7 years...) and putting this thread in
that context.

As I understand it:

 1. the standard doesn't say %B/MON_ should be genitive or nominative
 2. the standard does say UB for %O'x', x not in the list
 3. the current glibc %B/MON_ returns nominative
 4. the BSD/POSIX (proposed) %OB/ALTMON_ returns nominative

So your patch is changing the behaviour of the format specifier %B in a
way allowable by the standard, and it adds a non-standard extension %OB
which the standard explicitly states is undefined, but not disallowed.
Additionally, binaries built against pre-%OB glibc running on post-%OB
glibc will still have the old behaviour.

I'm fine what that; I had a different version of this in my mind (see
below).  Thank you for prompting me to give this more thought.  You are
definitely between a rock and hard place.  :)

I think I should respond to Florian's objection [5] at this point.

Florian,

Were you opposed to the work of trying to make %B a little smarter?  It
looks like Rafal abandoned that approach voluntarily, and opted to chase
the unification on the horizon when it was pointed out BSD and the POSIX
proposal were actually the same.  [6]

I was originally opposed to the idea of making %B act differently in
different contexts where it didn't before, but in light of the fact the
implementation isn't restricted to a particular format/case, that does
seem a reasonable compromise.  The POSIX proposal is 6-1/2 years old
now, barely younger than this bug, and we have someone who is interested
in fixing it *now*, in a way that keeps us flexible for whatever happens
with the standards, who-knows-when.  We could avoid a new specifier
extension (in lieu of standardization), and %B could be viewed as
partially "fixed", in that it just might get it right more often than it
already does.

The bug is about returning the correct case, in a context we might be
able to determine, not whether we should define our own standard for %B
or an extension %OB.  Could we avoid addressing the whole future
standards issue by limiting the fix to making %B return genitive in
cases where it can be sure it should, where the genitive is even available?

Rical

[1]
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap07.html#tag_07_03_05
[2] http://pubs.opengroup.org/onlinepubs/009695399/functions/strftime.html
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=10871
[4] http://austingroupbugs.net/view.php?id=258
[5] https://sourceware.org/ml/libc-alpha/2016-11/msg00322.html
[6] https://sourceware.org/bugzilla/show_bug.cgi?id=10871#c40