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Re: use v5.36; use warnings;

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From:
Dan Book
Date:
June 18, 2021 20:24
Subject:
Re: use v5.36; use warnings;
Message ID:
CABMkAVWiDAXhnO7iBEyzL0Ns_ay=Z=LPqK2YUK3nh45pA1VGtQ@mail.gmail.com
On Fri, Jun 18, 2021 at 3:26 PM Ricardo Signes <perl.p5p@rjbs.manxome.org>
wrote:

> On Sun, Jun 6, 2021, at 8:03 PM, Ricardo Signes wrote:
>
> I think I need to give it a big think, but here's the reasoning as I was
> able to quickly swap it back in:
>
> […]
> At ten years' remove, I'm not sure what I think of this decision anymore,
> but I urge you to read the reasoning behind it before coming to a
> conclusion.
>
>
> If you don't know what I'm quoting, I urge you to read my previous message
> and, just maybe, the 2011-ish thread it's summarizing.
>
> This topic got a bunch of PSC discussion.  In the end, I promised to write
> things up, so here I am.
>
> The idea, as I summarized previously, was that we wanted to make "use
> v5.40" work like "reset to defaults, then turn on all the v5.40 stuff".
> This meant that:
>
>    - "use v5.10" means "use feature 'say'" so "use v5.8" should mean "no
>    feature 'say'"
>    - so similarly: "use v5.12" means "use strict" so "use v5.10" should
>    mean "no strict"
>    - but some people had already been writing "use strict; use warnings;
>    use v5.10.0" and we didn't want to hurt them
>
>
> The point I advocated in a call with Neil and Nick was that our real
> problem was not clearly defining the *kinds* of actions that "use vX"
> might take.  We acted like it took one action:  "alter the semantics of the
> scope."   But some of those actions were hard to rationalize, especially
> after the fact.  Then, we left some things surprising:  If you say "no
> feature 'say'; use v5.10" you'll end up with say enabled.  So, "use
> feature" is not sticky in the same way that "use strict" is.
>
> I think this whole thing was a mess, and it was a mess on my watch, and I
> regret it.
>
> I think we should declare that "use vX" does this:
>
>    - use feature ":default"; use feature ":X";
>    - use xyz; (for various xyz);
>
> That means it would unconditionally turn on strict.  If we add warnings,
> it will unconditionally turn on warnings.
>
> Right now, I believe the *only* effect this will have is that code which
> has says "no strict; use v5.12.0", which would now begin turning on
> strictures.  We can detect this, for now, and issue a deprecation-style
> "this will turn on warnings in v5.40" starting in v5.36, but can begin
> having "use warnings" follow this rule from the start.
>
> I think this is the right way to go, even though it's a bit of a pain.
>

This sounds reasonable to me. We should *not* retroactively make it turn
off strict or warnings on older versions, but unconditionally enabling it
on the new versions would be more intuitive.

-Dan

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