perlpolicy - Various and sundry policies and commitments related to the Perl core
This document is the master document which records all written policies about how the Perl 5 Porters collectively develop and maintain the Perl core.
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:
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.
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.
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.
We will not provide security updates or bug fixes for development releases of Perl.
We encourage vendors to ship the most recent supported release of Perl at the time of their code freeze.
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 <[email protected]> to begin that process.
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.
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.
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.
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.
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.
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.
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.
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.
Acceptable documentation updates are those that correct factual errors, explain significant bugs or deficiencies in the current implementation, or fix broken markup.
Patches that add new warnings or errors or deprecate features are not acceptable.
Patches that fix crashing bugs that do not otherwise change Perl's functionality or negatively impact performance are acceptable.
Patches that fix CVEs or security issues are acceptable, but should be run through the [email protected] mailing list rather than applied directly.
Updates to dual-life modules should consist of minimal patches to fix crashing or security issues (as above).
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.
New versions of dual-life modules should NOT be imported into maint. Those belong in the next stable series.
Patches that add or remove features are not acceptable.
Patches that break binary compatibility are not acceptable. (Please talk to a pumpking.)
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.)