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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.
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 stabilty 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'. As of the release of 5.14.0, we will
"officially" end support for Perl 5.10, 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
initially released 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-reportATperl.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 thecore 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 core.
removed
Once a feature, construct or module has been marked as deprecated for a stable release cycle, we may remove it from
the 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 Documentation updates are acceptable.
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-reportATperl.org
mailing list rather than applied directly.
o Updates to dual-life modules should consist of minimal patches to fix crashing or security issues (as above).
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 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 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 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 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.
CREDITS
Social Contract about Contributed Modules originally by Russ Allbery <rraATstanford.edu> and the perl5-porters.
perl v5.12.4 2011-06-07 PERLPOLICY(1)
