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PERLPOLICY(1) Perl Programmers Reference Guide PERLPOLICY(1)
NAME
perlpolicy - Various and sundry policies and commitments related to the Perl core
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.
GOVERNANCE
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:
1. Larry is always by definition right about how Perl should behave. This means he has
final veto power on the core functionality.
2. Larry is allowed to change his mind about any matter at a later date, regardless of
whether he previously invoked Rule 1.
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.
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:
o 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.
o 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.
o 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.
o We will not provide security updates or bug fixes for development releases of Perl.
o We encourage vendors to ship the most recent supported release of Perl at the time of
their code freeze.
o 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 <perl5-security-report AT perl.org> to begin that process.
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.
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.
experimental
If something in the Perl core is marked as 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.
deprecated
If something in the Perl core is marked as deprecated, we may remove it from the core
in the next stable release series, though we may not. As of Perl 5.12, deprecated
features and modules warn the user as they're used. If you use a deprecated feature
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.
discouraged
From time to time, we may mark language constructs and features which we consider to
have been mistakes as discouraged. Discouraged features aren't candidates for removal
in the next major release series, but we may later deprecate them if they're found to
stand in the way of a significant improvement to the Perl core.
removed
Once a feature, construct or module has been marked as deprecated for a stable release
cycle, we may remove it from the Perl core. Unsurprisingly, we say we've removed
these things.
MAINTENANCE BRANCHES
o 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.
o 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.
o Acceptable documentation updates are those that correct factual errors, explain
significant bugs or deficiencies in the current implementation, or fix broken markup.
o Patches that add new warnings or errors or deprecate features are not acceptable.
o Patches that fix crashing bugs that do not otherwise change Perl's functionality or
negatively impact performance are acceptable.
o Patches that fix CVEs or security issues are acceptable, but should be run through the
perl5-security-report AT perl.org mailing list rather than applied directly.
o Patches that fix regressions in perl's behavior relative to previous releases are
acceptable.
o Updates to dual-life modules should consist of minimal patches to fix crashing or
security issues (as above).
o 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.
o New versions of dual-life modules should NOT be imported into maint. Those belong in
the next stable series.
o Patches that add or remove features are not acceptable.
o Patches that break binary compatibility are not acceptable. (Please talk to a
pumpking.)
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, we're going to try out a new process for
maint-5.12.
Any committer may cherry-pick any commit from blead to maint-5.12 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.)
CONTRIBUTED MODULES
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:
o 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.
o 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.
o 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.
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 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.
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 "use strict" and "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 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.
CREDITS
"Social Contract about Contributed Modules" originally by Russ Allbery <rra AT stanford.edu>
and the perl5-porters.
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