Reapply "docs: clarify effect of $^H, %^H, ${^WARNING_BITS}"

[perl5.git] / pod / perlpolicy.pod

=encoding utf8

=head1 NAME

perlpolicy - Various and sundry policies and commitments related to the Perl core

=head1 DESCRIPTION

This document is the master document which records all written
policies about how the Perl 5 Porters collectively develop and maintain
the Perl core.

=head1 GOVERNANCE

=head2 Perl 5 Porters

Subscribers to perl5-porters (the porters themselves) come in several flavours.
Some are quiet curious lurkers, who rarely pitch in and instead watch
the ongoing development to ensure they're forewarned of new changes or
features in Perl.  Some are representatives of vendors, who are there
to make sure that Perl continues to compile and work on their
platforms.  Some patch any reported bug that they know how to fix,
some are actively patching their pet area (threads, Win32, the regexp
-engine), while others seem to do nothing but complain.  In other
words, it's your usual mix of technical people.

Among these people are the core Perl team.  These are trusted volunteers
involved in the ongoing development of the Perl language and interpreter.
They are not required to be language developers or committers.

Over this group of porters presides Larry Wall.  He has the final word
in what does and does not change in any of the Perl programming languages.
These days, Larry spends most of his time on Raku, while Perl 5 is
shepherded by a steering council of porters responsible for deciding what
goes into each release and ensuring that releases happen on a regular
basis.

Larry sees Perl development along the lines of the US government:
there's the Legislature (the porters, represented by the core team), the
Executive branch (the steering council), and the Supreme Court (Larry).
The legislature can discuss and submit patches to the executive branch
all they like, but the executive branch is free to veto them.  Rarely,
the Supreme Court will side with the executive branch over the
legislature, or the legislature over the executive branch.  Mostly,
however, the legislature and the executive branch are supposed to get
along and work out their differences without impeachment or court cases.

You might sometimes see reference to Rule 1 and Rule 2.  Larry's power
as Supreme Court is expressed in The Rules:

=over 4

=item 1

Larry is always by definition right about how Perl should behave.
This means he has final veto power on the core functionality.

=item 2

Larry is allowed to change his mind about any matter at a later date,
regardless of whether he previously invoked Rule 1.

=back

Got that?  Larry is always right, even when he was wrong.  It's rare
to see either Rule exercised, but they are often alluded to.

For the specifics on how the members of the core team and steering
council are elected or rotated, consult L<perlgov>, which spells it all
out in detail.

=head1 MAINTENANCE AND SUPPORT

Perl 5 is developed by a community, not a corporate entity. Every change
contributed to the Perl core is the result of a donation. Typically, these
donations are contributions of code or time by individual members of our
community. On occasion, these donations come in the form of corporate
or organizational sponsorship of a particular individual or project.

As a volunteer organization, the commitments we make are heavily dependent
on the goodwill and hard work of individuals who have no obligation to
contribute to Perl.

That being said, we value Perl's stability and security and have long
had an unwritten covenant with the broader Perl community to support
and maintain releases of Perl.

This document codifies the support and maintenance commitments that
the Perl community should expect from Perl's developers:

=over

=item *

We "officially" support the two most recent stable release series.  5.30.x
and earlier are now out of support.  As of the release of 5.36.0, we will
"officially" end support for Perl 5.32.x, other than providing security
updates as described below.

=item *

To the best of our ability, we will attempt to fix critical issues
in the two most recent stable 5.x release series.  Fixes for the
current release series take precedence over fixes for the previous
release series.

=item *

To the best of our ability, we will provide "critical" security patches
/ releases for any major version of Perl whose 5.x.0 release was within
the past three years.  We can only commit to providing these for the
most recent .y release in any 5.x.y series.

=item *

We will not provide security updates or bug fixes for development
releases of Perl.

=item *

We encourage vendors to ship the most recent supported release of
Perl at the time of their code freeze.

=item *

As a vendor, you may have a requirement to backport security fixes
beyond our 3 year support commitment.  We can provide limited support and
advice to you as you do so and, where possible will try to apply
those patches to the relevant -maint branches in git, though we may or
may not choose to make numbered releases or "official" patches
available. See L<perlsec/SECURITY VULNERABILITY CONTACT INFORMATION>
for details on how to begin that process.

=back

=head1 BACKWARD COMPATIBILITY AND DEPRECATION

Our community has a long-held belief that backward-compatibility is a
virtue, even when the functionality in question is a design flaw.

We would all love to unmake some mistakes we've made over the past
decades.  Living with every design error we've ever made can lead
to painful stagnation.  Unwinding our mistakes is very, very
difficult.  Doing so without actively harming our users is
nearly impossible.

Lately, ignoring or actively opposing compatibility with earlier versions
of Perl has come into vogue.  Sometimes, a change is proposed which
wants to usurp syntax which previously had another meaning.  Sometimes,
a change wants to improve previously-crazy semantics.

Down this road lies madness.

Requiring end-user programmers to change just a few language constructs,
even language constructs which no well-educated developer would ever
intentionally use is tantamount to saying "you should not upgrade to
a new release of Perl unless you have 100% test coverage and can do a
full manual audit of your codebase."  If we were to have tools capable of
reliably upgrading Perl source code from one version of Perl to another,
this concern could be significantly mitigated.

We want to ensure that Perl continues to grow and flourish in the coming
years and decades, but not at the expense of our user community.

Existing syntax and semantics should only be marked for destruction in
very limited circumstances.  If they are believed to be very rarely used,
stand in the way of actual improvement to the Perl language or perl
interpreter, and if affected code can be easily updated to continue
working, they may be considered for removal.  When in doubt, caution
dictates that we will favor backward compatibility.  When a feature is
deprecated, a statement of reasoning describing the decision process
will be posted, and a link to it will be provided in the relevant
perldelta documents.

Using a lexical pragma to enable or disable legacy behavior should be
considered when appropriate, and in the absence of any pragma legacy
behavior should be enabled.  Which backward-incompatible changes are
controlled implicitly by a 'use v5.x.y' is a decision which should be
made by the steering council in consultation with the community.

Historically, we've held ourselves to a far higher standard than
backward-compatibility -- bugward-compatibility.  Any accident of
implementation or unintentional side-effect of running some bit of code
has been considered to be a feature of the language to be defended with
the same zeal as any other feature or functionality.  No matter how
frustrating these unintentional features may be to us as we continue
to improve Perl, these unintentional features often deserve our
protection.  It is very important that existing software written in
Perl continue to work correctly.  If end-user developers have adopted a
bug as a feature, we need to treat it as such.

New syntax and semantics which don't break existing language constructs
and syntax have a much lower bar.  They merely need to prove themselves
to be useful, elegant, well designed, and well tested.  In most cases,
these additions will be marked as I<experimental> for some time.  See
below for more on that.

=head2 Terminology

To make sure we're talking about the same thing when we discuss the removal
of features or functionality from the Perl core, we have specific definitions
for a few words and phrases.

=over

=item experimental

If something in the Perl core is marked as B<experimental>, we may change
its behaviour, deprecate or remove it without notice. While we'll always
do our best to smooth the transition path for users of experimental
features, you should contact the perl5-porters mailinglist if you find
an experimental feature useful and want to help shape its future.

Experimental features must be experimental in two stable releases before being
marked non-experimental.  Experimental features will only have their
experimental status revoked when they no longer have any design-changing bugs
open against them and when they have remained unchanged in behavior for the
entire length of a development cycle.  In other words, a feature present in
v5.20.0 may be marked no longer experimental in v5.22.0 if and only if its
behavior is unchanged throughout all of v5.21.

=item deprecated

If something in the Perl core is marked as B<deprecated>, we may remove it
from the core in the future, though we might not.  Generally, backward
incompatible changes will have deprecation warnings for two release
cycles before being removed, but may be removed after just one cycle if
the risk seems quite low or the benefits quite high.

As of
Perl 5.12, deprecated features and modules warn the user as they're used.
When a module is deprecated, it will also be made available on CPAN.
Installing it from CPAN will silence deprecation warnings for that module.

If you use a deprecated feature or module and believe that its removal from
the Perl core would be a mistake, please contact the perl5-porters
mailinglist and plead your case.  We don't deprecate things without a good
reason, but sometimes there's a counterargument we haven't considered.
Historically, we did not distinguish between "deprecated" and "discouraged"
features.

=item discouraged

From time to time, we may mark language constructs and features which we
consider to have been mistakes as B<discouraged>.  Discouraged features
aren't currently candidates for removal, but
we may later deprecate them if they're found to stand in the way of a
significant improvement to the Perl core.

=item removed

Once a feature, construct or module has been marked as deprecated, we
may remove it from the Perl core.  Unsurprisingly,
we say we've B<removed> these things.  When a module is removed, it will
no longer ship with Perl, but will continue to be available on CPAN.

=back

=head1 MAINTENANCE BRANCHES

New releases of maintenance branches should only contain changes that fall into
one of the "acceptable" categories set out below, but must not contain any
changes that fall into one of the "unacceptable" categories.  (For example, a
fix for a crashing bug must not be included if it breaks binary compatibility.)

It is not necessary to include every change meeting these criteria, and in
general the focus should be on addressing security issues, crashing bugs,
regressions and serious installation issues.  The temptation to include a
plethora of minor changes that don't affect the installation or execution of
perl (e.g. spelling corrections in documentation) should be resisted in order
to reduce the overall risk of overlooking something.  The intention is to
create maintenance releases which are both worthwhile and which users can have
full confidence in the stability of.  (A secondary concern is to avoid burning
out the maint-release manager or overwhelming other committers voting on
changes to be included (see L</"Getting changes into a maint branch">
below).)

The following types of change may be considered acceptable, as long as they do
not also fall into any of the "unacceptable" categories set out below:

=over

=item *

Patches that fix CVEs or security issues.  These changes should
be passed using the security reporting mechanism rather than applied
directly; see L<perlsec/SECURITY VULNERABILITY CONTACT INFORMATION>.

=item *

Patches that fix crashing bugs, assertion failures and
memory corruption but which do not otherwise change perl's
functionality or negatively impact performance.

=item *

Patches that fix regressions in perl's behavior relative to previous
releases, no matter how old the regression, since some people may
upgrade from very old versions of perl to the latest version.

=item *

Patches that fix bugs in features that were new in the corresponding 5.x.0
stable release.

=item *

Patches that fix anything which prevents or seriously impacts the build
or installation of perl.

=item *

Portability fixes, such as changes to Configure and the files in
the hints/ folder.

=item *

Minimal patches that fix platform-specific test failures.

=item *

Documentation updates that correct factual errors, explain significant
bugs or deficiencies in the current implementation, or fix broken markup.

=item *

Updates to dual-life modules should consist of minimal patches to
fix crashing bugs or security issues (as above).  Any changes made to
dual-life modules for which CPAN is canonical should be coordinated with
the upstream author.

=back

The following types of change are NOT acceptable:

=over

=item *

Patches that break binary compatibility.  (Please talk to the steering
council.)

=item *

Patches that add or remove features.

=item *

Patches that add new warnings or errors or deprecate features.

=item *

Ports of Perl to a new platform, architecture or OS release that
involve changes to the implementation.

=item *

New versions of dual-life modules should NOT be imported into maint.
Those belong in the next stable series.

=back

If there is any question about whether a given patch might merit
inclusion in a maint release, then it almost certainly should not
be included.

=head2 Getting changes into a maint branch

Historically, only the single-person project manager cherry-picked
changes from bleadperl into maintperl.  This has scaling problems.  At
the same time, maintenance branches of stable versions of Perl need to
be treated with great care.  To that end, as of Perl 5.12, we have a new
process for maint branches.

Any committer may cherry-pick any commit from blead to a maint branch by
first adding an entry to the relevant voting file in the maint-votes branch
announcing the commit as a candidate for back-porting, and then waiting for
at least two other committers to add their votes in support of this (i.e. a
total of at least three votes is required before a commit may be back-ported).

Most of the work involved in both rounding up a suitable set of candidate
commits and cherry-picking those for which three votes have been cast will
be done by the maint branch release manager, but anyone else is free to add
other proposals if they're keen to ensure certain fixes don't get overlooked
or fear they already have been.

Other voting mechanisms may also be used instead (e.g. sending mail to
perl5-porters and at least two other committers responding to the list
giving their assent), as long as the same number of votes is gathered in a
transparent manner.  Specifically, proposals of which changes to cherry-pick
must be visible to everyone on perl5-porters so that the views of everyone
interested may be heard.

It is not necessary for voting to be held on cherry-picking perldelta
entries associated with changes that have already been cherry-picked, nor
for the maint-release manager to obtain votes on changes required by the
F<Porting/release_managers_guide.pod> where such changes can be applied by
the means of cherry-picking from blead.

=head1 CONTRIBUTED MODULES


=head2 A Social Contract about Artistic Control

What follows is a statement about artistic control, defined as the ability
of authors of packages to guide the future of their code and maintain
control over their work.  It is a recognition that authors should have
control over their work, and that it is a responsibility of the rest of
the Perl community to ensure that they retain this control.  It is an
attempt to document the standards to which we, as Perl developers, intend
to hold ourselves.  It is an attempt to write down rough guidelines about
the respect we owe each other as Perl developers.

This statement is not a legal contract.  This statement is not a legal
document in any way, shape, or form.  Perl is distributed under the GNU
Public License and under the Artistic License; those are the precise legal
terms.  This statement isn't about the law or licenses.  It's about
community, mutual respect, trust, and good-faith cooperation.

We recognize that the Perl core, defined as the software distributed with
the heart of Perl itself, is a joint project on the part of all of us.
From time to time, a script, module, or set of modules (hereafter referred
to simply as a "module") will prove so widely useful and/or so integral to
the correct functioning of Perl itself that it should be distributed with
the Perl core.  This should never be done without the author's explicit
consent, and a clear recognition on all parts that this means the module
is being distributed under the same terms as Perl itself.  A module author
should realize that inclusion of a module into the Perl core will
necessarily mean some loss of control over it, since changes may
occasionally have to be made on short notice or for consistency with the
rest of Perl.

Once a module has been included in the Perl core, however, everyone
involved in maintaining Perl should be aware that the module is still the
property of the original author unless the original author explicitly
gives up their ownership of it.  In particular:

=over

=item *

The version of the module in the Perl core should still be considered the
work of the original author.  All patches, bug reports, and so
forth should be fed back to them.  Their development directions
should be respected whenever possible.

=item *

Patches may be applied by the steering council without the explicit
cooperation of the module author if and only if they are very minor,
time-critical in some fashion (such as urgent security fixes), or if
the module author cannot be reached.  Those patches must still be
given back to the author when possible, and if the author decides on
an alternate fix in their version, that fix should be strongly
preferred unless there is a serious problem with it.  Any changes not
endorsed by the author should be marked as such, and the contributor
of the change acknowledged.

=item *

The version of the module distributed with Perl should, whenever
possible, be the latest version of the module as distributed by the
author (the latest non-beta version in the case of public Perl
releases), although the steering council may hold off on upgrading the
version of the module distributed with Perl to the latest version
until the latest version has had sufficient testing.

=back

In other words, the author of a module should be considered to have final
say on modifications to their module whenever possible (bearing in mind
that it's expected that everyone involved will work together and arrive at
reasonable compromises when there are disagreements).

As a last resort, however:

If the author's vision of the future of their module is sufficiently
different from the vision of the steering council and perl5-porters as a
whole so as to cause serious problems for Perl, the steering council may
choose to formally fork the version of the module in the Perl core from the
one maintained by the author.  This should not be done lightly and
should B<always> if at all possible be done only after direct input
from Larry.  If this is done, it must then be made explicit in the
module as distributed with the Perl core that it is a forked version and
that while it is based on the original author's work, it is no longer
maintained by them.  This must be noted in both the documentation and
in the comments in the source of the module.

Again, this should be a last resort only.  Ideally, this should never
happen, and every possible effort at cooperation and compromise should be
made before doing this.  If it does prove necessary to fork a module for
the overall health of Perl, proper credit must be given to the original
author in perpetuity and the decision should be constantly re-evaluated to
see if a remerging of the two branches is possible down the road.

In all dealings with contributed modules, everyone maintaining Perl should
keep in mind that the code belongs to the original author, that they may
not be on perl5-porters at any given time, and that a patch is not
official unless it has been integrated into the author's copy of the
module.  To aid with this, and with points #1, #2, and #3 above, contact
information for the authors of all contributed modules should be kept with
the Perl distribution.

Finally, the Perl community as a whole recognizes that respect for
ownership of code, respect for artistic control, proper credit, and active
effort to prevent unintentional code skew or communication gaps is vital
to the health of the community and Perl itself.  Members of a community
should not normally have to resort to rules and laws to deal with each
other, and this document, although it contains rules so as to be clear, is
about an attitude and general approach.  The first step in any dispute
should be open communication, respect for opposing views, and an attempt
at a compromise.  In nearly every circumstance nothing more will be
necessary, and certainly no more drastic measure should be used until
every avenue of communication and discussion has failed.


=head1 DOCUMENTATION

Perl's documentation is an important resource for our users. It's
incredibly important for Perl's documentation to be reasonably coherent
and to accurately reflect the current implementation.

Just as P5P collectively maintains the codebase, we collectively
maintain the documentation.  Writing a particular bit of documentation
doesn't give an author control of the future of that documentation.
At the same time, just as source code changes should match the style
of their surrounding blocks, so should documentation changes.

Examples in documentation should be illustrative of the concept
they're explaining.  Sometimes, the best way to show how a
language feature works is with a small program the reader can
run without modification.  More often, examples will consist
of a snippet of code containing only the "important" bits.
The definition of "important" varies from snippet to snippet.
Sometimes it's important to declare C<use strict> and C<use warnings>,
initialize all variables and fully catch every error condition.
More often than not, though, those things obscure the lesson
the example was intended to teach.

As Perl is developed by a global team of volunteers, our
documentation often contains spellings which look funny
to I<somebody>.  Choice of American/British/Other spellings
is left as an exercise for the author of each bit of
documentation.  When patching documentation, try to emulate
the documentation around you, rather than changing the existing
prose.

In general, documentation should describe what Perl does "now" rather
than what it used to do.  It's perfectly reasonable to include notes
in documentation about how behaviour has changed from previous releases,
but, with very few exceptions, documentation isn't "dual-life" --
it doesn't need to fully describe how all old versions used to work.

=head1 STANDARDS OF CONDUCT

The official forum for the development of perl is the perl5-porters mailing
list, mentioned above, and its bugtracker at GitHub.  Posting to the
list and the bugtracker is not a right: all participants in discussion are
expected to adhere to a standard of conduct.

=over 4

=item *

Always be civil.

=item *

Heed the moderators.

=back

Civility is simple: stick to the facts while avoiding demeaning remarks,
belittling other individuals, sarcasm, or a presumption of bad faith. It is
not enough to be factual.  You must also be civil.  Responding in kind to
incivility is not acceptable.  If you relay otherwise-unposted comments to
the list from a third party, you take responsibility for the content of
those comments, and you must therefore ensure that they are civil.

While civility is required, kindness is encouraged; if you have any doubt about
whether you are being civil, simply ask yourself, "Am I being kind?" and aspire
to that.

If the list moderators tell you that you are not being civil, carefully
consider how your words have appeared before responding in any way.  Were they
kind?  You may protest, but repeated protest in the face of a repeatedly
reaffirmed decision is not acceptable.  Repeatedly protesting about the
moderators' decisions regarding a third party is also unacceptable, as is
continuing to initiate off-list contact with the moderators about their
decisions.

Unacceptable behavior will result in a public and clearly identified
warning.  A second instance of unacceptable behavior from the same
individual will result in removal from the mailing list and GitHub issue
tracker, for a period of one calendar month.  The rationale for this is to
provide an opportunity for the person to change the way they act.

After the time-limited ban has been lifted, a third instance of
unacceptable behavior will result in a further public warning.  A fourth
or subsequent instance will result in an indefinite ban.  The rationale
is that, in the face of an apparent refusal to change behavior, we must
protect other community members from future unacceptable actions.  The
moderators may choose to lift an indefinite ban if the person in
question affirms they will not transgress again.

Removals, like warnings, are public.

The list of moderators will be public knowledge.  At present, it is:
Karen Etheridge, Neil Bowers, Nicholas Clark, Ricardo Signes, Todd Rinaldo.

=head1 CREDITS

"Social Contract about Contributed Modules" originally by Russ Allbery E<lt>rra@stanford.eduE<gt> and the perl5-porters.