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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