Unused dTHX, even under threads.

[perl5.git] / pod / perlpolicy.pod

=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.

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 Perl 6, while Perl 5 is
shepherded by a "pumpking", a porter 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), the Executive branch (the
-pumpking), 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.

=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.  5.12.x
and earlier are now out of support.  As of the release of 5.18.0, we will
"officially" end support for Perl 5.14.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.  Contact us at E<lt>perl5-security-report@perl.orgE<gt>
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 a given language feature's continued
inclusion in the language will cause significant harm to the language
or prevent us from making needed changes to the runtime, then it may
be considered for deprecation.

Any language change which breaks backward-compatibility should be able to
be enabled or disabled lexically.  Unless code at a given scope declares
that it wants the new behavior, that new behavior should be disabled.
Which backward-incompatible changes are controlled implicitly by a
'use v5.x.y' is a decision which should be made by the pumpking in
consultation with the community.

When a backward-incompatible change can't be toggled lexically, the decision
to change the language must be considered very, very carefully.  If it's
possible to move the old syntax or semantics out of the core language
and into XS-land, that XS module should be enabled by default unless
the user declares that they want a newer revision of Perl.

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.

=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.

=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

=over

=item *

New releases of maint should contain as few changes as possible.
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.

=item *

Portability fixes, such as changes to Configure and the files in
hints/ are acceptable. Ports of Perl to a new platform, architecture
or OS release that involve changes to the implementation are NOT
acceptable.

=item *

Acceptable documentation updates are those that correct factual errors,
explain significant bugs or deficiencies in the current implementation, 
or fix broken markup.

=item *

Patches that add new warnings or errors or deprecate features
are not acceptable.

=item *

Patches that fix crashing bugs that do not otherwise change Perl's
functionality or negatively impact performance are acceptable.  

=item *

Patches that fix CVEs or security issues are acceptable, but should
be run through the perl5-security-report@perl.org mailing list
rather than applied directly.

=item *

Patches that fix regressions in perl's behavior relative to previous
releases are acceptable.

=item *

Updates to dual-life modules should consist of minimal patches to 
fix crashing or security issues (as above).

=item *

Minimal patches that fix platform-specific test failures or
installation issues are acceptable. When these changes are made
to dual-life modules for which CPAN is canonical, any changes
should be coordinated with the upstream author.

=item *

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

=item *

Patches that add or remove features are not acceptable.

=item *

Patches that break binary compatibility are not acceptable.  (Please
talk to a pumpking.)

=back


=head2 Getting changes into a maint branch

Historically, only the pumpking 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 if
they send mail to perl5-porters announcing their intent to cherry-pick
a specific commit along with a rationale for doing so and at least two 
other committers respond to the list giving their assent. (This policy
applies to current and former pumpkings, as well as other committers.)

=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 pumpkin holder 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 pumpkin holder 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 pumpkin holder and perl5-porters as a
whole so as to cause serious problems for Perl, the pumpkin holder 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 CREDITS

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