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48cb5b3a 1=head1 NAME
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9a7064ee 3perlpolicy - Various and sundry policies and commitments related to the Perl core
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4
5=head1 DESCRIPTION
6
7This document is the master document which records all written
8policies about how the Perl 5 Porters collectively develop and maintain
9the Perl core.
10
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11=head1 GOVERNANCE
12
13=head2 Perl 5 Porters
14
15Subscribers to perl5-porters (the porters themselves) come in several flavours.
16Some are quiet curious lurkers, who rarely pitch in and instead watch
17the ongoing development to ensure they're forewarned of new changes or
18features in Perl. Some are representatives of vendors, who are there
19to make sure that Perl continues to compile and work on their
20platforms. Some patch any reported bug that they know how to fix,
21some are actively patching their pet area (threads, Win32, the regexp
22-engine), while others seem to do nothing but complain. In other
23words, it's your usual mix of technical people.
24
25Over this group of porters presides Larry Wall. He has the final word
26in what does and does not change in any of the Perl programming languages.
27These days, Larry spends most of his time on Perl 6, while Perl 5 is
28shepherded by a "pumpking", a porter responsible for deciding what
29goes into each release and ensuring that releases happen on a regular
30basis.
31
32Larry sees Perl development along the lines of the US government:
33there's the Legislature (the porters), the Executive branch (the
34-pumpking), and the Supreme Court (Larry). The legislature can
35discuss and submit patches to the executive branch all they like, but
36the executive branch is free to veto them. Rarely, the Supreme Court
37will side with the executive branch over the legislature, or the
38legislature over the executive branch. Mostly, however, the
39legislature and the executive branch are supposed to get along and
40work out their differences without impeachment or court cases.
41
42You might sometimes see reference to Rule 1 and Rule 2. Larry's power
43as Supreme Court is expressed in The Rules:
44
45=over 4
46
47=item 1
48
49Larry is always by definition right about how Perl should behave.
50This means he has final veto power on the core functionality.
51
52=item 2
53
54Larry is allowed to change his mind about any matter at a later date,
55regardless of whether he previously invoked Rule 1.
56
57=back
58
59Got that? Larry is always right, even when he was wrong. It's rare
60to see either Rule exercised, but they are often alluded to.
61
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62=head1 MAINTENANCE AND SUPPORT
63
64Perl 5 is developed by a community, not a corporate entity. Every change
65contributed to the Perl core is the result of a donation. Typically, these
66donations are contributions of code or time by individual members of our
67community. On occasion, these donations come in the form of corporate
68or organizational sponsorship of a particular individual or project.
69
70As a volunteer organization, the commitments we make are heavily dependent
71on the goodwill and hard work of individuals who have no obligation to
72contribute to Perl.
73
3b4ebcde 74That being said, we value Perl's stability and security and have long
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75had an unwritten covenant with the broader Perl community to support
76and maintain releases of Perl.
77
78This document codifies the support and maintenance commitments that
79the Perl community should expect from Perl's developers:
80
81=over
82
83=item *
84
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85We "officially" support the two most recent stable release series. 5.12.x
86and earlier are now out of support. As of the release of 5.18.0, we will
87"officially" end support for Perl 5.14.x, other than providing security
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88updates as described below.
89
90=item *
91
92To the best of our ability, we will attempt to fix critical issues
e26b5c49 93in the two most recent stable 5.x release series. Fixes for the
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94current release series take precedence over fixes for the previous
95release series.
96
97=item *
98
99To the best of our ability, we will provide "critical" security patches
f50f542d 100/ releases for any major version of Perl whose 5.x.0 release was within
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101the past three years. We can only commit to providing these for the
102most recent .y release in any 5.x.y series.
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103
104=item *
105
106We will not provide security updates or bug fixes for development
107releases of Perl.
108
109=item *
110
111We encourage vendors to ship the most recent supported release of
112Perl at the time of their code freeze.
113
114=item *
115
116As a vendor, you may have a requirement to backport security fixes
117beyond our 3 year support commitment. We can provide limited support and
118advice to you as you do so and, where possible will try to apply
119those patches to the relevant -maint branches in git, though we may or
120may not choose to make numbered releases or "official" patches
121available. Contact us at E<lt>perl5-security-report@perl.orgE<gt>
122to begin that process.
123
124=back
125
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126=head1 BACKWARD COMPATIBILITY AND DEPRECATION
127
128Our community has a long-held belief that backward-compatibility is a
129virtue, even when the functionality in question is a design flaw.
130
131We would all love to unmake some mistakes we've made over the past
132decades. Living with every design error we've ever made can lead
133to painful stagnation. Unwinding our mistakes is very, very
134difficult. Doing so without actively harming our users is
135nearly impossible.
136
137Lately, ignoring or actively opposing compatibility with earlier versions
138of Perl has come into vogue. Sometimes, a change is proposed which
139wants to usurp syntax which previously had another meaning. Sometimes,
339a461d 140a change wants to improve previously-crazy semantics.
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141
142Down this road lies madness.
143
144Requiring end-user programmers to change just a few language constructs,
145even language constructs which no well-educated developer would ever
146intentionally use is tantamount to saying "you should not upgrade to
147a new release of Perl unless you have 100% test coverage and can do a
148full manual audit of your codebase." If we were to have tools capable of
149reliably upgrading Perl source code from one version of Perl to another,
150this concern could be significantly mitigated.
151
152We want to ensure that Perl continues to grow and flourish in the coming
153years and decades, but not at the expense of our user community.
154
155Existing syntax and semantics should only be marked for destruction in
156very limited circumstances. If a given language feature's continued
157inclusion in the language will cause significant harm to the language
158or prevent us from making needed changes to the runtime, then it may
159be considered for deprecation.
160
161Any language change which breaks backward-compatibility should be able to
162be enabled or disabled lexically. Unless code at a given scope declares
163that it wants the new behavior, that new behavior should be disabled.
164Which backward-incompatible changes are controlled implicitly by a
165'use v5.x.y' is a decision which should be made by the pumpking in
166consultation with the community.
167
168When a backward-incompatible change can't be toggled lexically, the decision
169to change the language must be considered very, very carefully. If it's
170possible to move the old syntax or semantics out of the core language
171and into XS-land, that XS module should be enabled by default unless
172the user declares that they want a newer revision of Perl.
173
174Historically, we've held ourselves to a far higher standard than
175backward-compatibility -- bugward-compatibility. Any accident of
176implementation or unintentional side-effect of running some bit of code
177has been considered to be a feature of the language to be defended with
178the same zeal as any other feature or functionality. No matter how
179frustrating these unintentional features may be to us as we continue
180to improve Perl, these unintentional features often deserve our
181protection. It is very important that existing software written in
182Perl continue to work correctly. If end-user developers have adopted a
183bug as a feature, we need to treat it as such.
184
185New syntax and semantics which don't break existing language constructs
186and syntax have a much lower bar. They merely need to prove themselves
b6538e4f 187to be useful, elegant, well designed, and well tested.
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188
189=head2 Terminology
190
191To make sure we're talking about the same thing when we discuss the removal
192of features or functionality from the Perl core, we have specific definitions
193for a few words and phrases.
194
195=over
196
197=item experimental
198
199If something in the Perl core is marked as B<experimental>, we may change
200its behaviour, deprecate or remove it without notice. While we'll always
201do our best to smooth the transition path for users of experimental
202features, you should contact the perl5-porters mailinglist if you find
203an experimental feature useful and want to help shape its future.
204
205=item deprecated
206
207If something in the Perl core is marked as B<deprecated>, we may remove it
3b4ebcde 208from the core in the next stable release series, though we may not. As of
70e4a83b 209Perl 5.12, deprecated features and modules warn the user as they're used.
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210When a module is deprecated, it will also be made available on CPAN.
211Installing it from CPAN will silence deprecation warnings for that module.
212
213If you use a deprecated feature or module and believe that its removal from
214the Perl core would be a mistake, please contact the perl5-porters
215mailinglist and plead your case. We don't deprecate things without a good
216reason, but sometimes there's a counterargument we haven't considered.
217Historically, we did not distinguish between "deprecated" and "discouraged"
218features.
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219
220=item discouraged
221
222From time to time, we may mark language constructs and features which we
223consider to have been mistakes as B<discouraged>. Discouraged features
224aren't candidates for removal in the next major release series, but
225we may later deprecate them if they're found to stand in the way of a
9a7064ee 226significant improvement to the Perl core.
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227
228=item removed
229
230Once a feature, construct or module has been marked as deprecated for a
9a7064ee 231stable release cycle, we may remove it from the Perl core. Unsurprisingly,
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232we say we've B<removed> these things. When a module is removed, it will
233no longer ship with Perl, but will continue to be available on CPAN.
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234
235=back
48cb5b3a 236
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237=head1 MAINTENANCE BRANCHES
238
239=over
240
241=item *
242
243New releases of maint should contain as few changes as possible.
244If there is any question about whether a given patch might merit
245inclusion in a maint release, then it almost certainly should not
246be included.
247
248=item *
249
250Portability fixes, such as changes to Configure and the files in
251hints/ are acceptable. Ports of Perl to a new platform, architecture
252or OS release that involve changes to the implementation are NOT
253acceptable.
254
255=item *
256
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257Acceptable documentation updates are those that correct factual errors,
258explain significant bugs or deficiencies in the current implementation,
259or fix broken markup.
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260
261=item *
262
263Patches that add new warnings or errors or deprecate features
264are not acceptable.
265
266=item *
267
268Patches that fix crashing bugs that do not otherwise change Perl's
269functionality or negatively impact performance are acceptable.
270
271=item *
272
273Patches that fix CVEs or security issues are acceptable, but should
274be run through the perl5-security-report@perl.org mailing list
275rather than applied directly.
276
277=item *
278
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279Patches that fix regressions in perl's behavior relative to previous
280releases are acceptable.
281
282=item *
283
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284Updates to dual-life modules should consist of minimal patches to
285fix crashing or security issues (as above).
286
287=item *
288
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289Minimal patches that fix platform-specific test failures or
290installation issues are acceptable. When these changes are made
291to dual-life modules for which CPAN is canonical, any changes
292should be coordinated with the upstream author.
293
294=item *
295
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296New versions of dual-life modules should NOT be imported into maint.
297Those belong in the next stable series.
298
299=item *
300
301Patches that add or remove features are not acceptable.
302
303=item *
304
305Patches that break binary compatibility are not acceptable. (Please
306talk to a pumpking.)
307
308=back
309
310
311=head2 Getting changes into a maint branch
312
313Historically, only the pumpking cherry-picked changes from bleadperl
314into maintperl. This has...scaling problems. At the same time,
315maintenance branches of stable versions of Perl need to be treated with
316great care. To that end, we're going to try out a new process for
317maint-5.12.
318
319Any committer may cherry-pick any commit from blead to maint-5.12 if
320they send mail to perl5-porters announcing their intent to cherry-pick
321a specific commit along with a rationale for doing so and at least two
322other committers respond to the list giving their assent. (This policy
323applies to current and former pumpkings, as well as other committers.)
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324
325=head1 CONTRIBUTED MODULES
326
327
328=head2 A Social Contract about Artistic Control
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329
330What follows is a statement about artistic control, defined as the ability
331of authors of packages to guide the future of their code and maintain
332control over their work. It is a recognition that authors should have
333control over their work, and that it is a responsibility of the rest of
334the Perl community to ensure that they retain this control. It is an
335attempt to document the standards to which we, as Perl developers, intend
336to hold ourselves. It is an attempt to write down rough guidelines about
337the respect we owe each other as Perl developers.
338
339This statement is not a legal contract. This statement is not a legal
340document in any way, shape, or form. Perl is distributed under the GNU
341Public License and under the Artistic License; those are the precise legal
342terms. This statement isn't about the law or licenses. It's about
343community, mutual respect, trust, and good-faith cooperation.
344
345We recognize that the Perl core, defined as the software distributed with
346the heart of Perl itself, is a joint project on the part of all of us.
aaa2bbb1 347From time to time, a script, module, or set of modules (hereafter referred
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348to simply as a "module") will prove so widely useful and/or so integral to
349the correct functioning of Perl itself that it should be distributed with
9a7064ee 350the Perl core. This should never be done without the author's explicit
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351consent, and a clear recognition on all parts that this means the module
352is being distributed under the same terms as Perl itself. A module author
353should realize that inclusion of a module into the Perl core will
354necessarily mean some loss of control over it, since changes may
355occasionally have to be made on short notice or for consistency with the
356rest of Perl.
357
358Once a module has been included in the Perl core, however, everyone
359involved in maintaining Perl should be aware that the module is still the
360property of the original author unless the original author explicitly
361gives up their ownership of it. In particular:
362
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363=over
364
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365=item *
366
9a7064ee 367The version of the module in the Perl core should still be considered the
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368work of the original author. All patches, bug reports, and so
369forth should be fed back to them. Their development directions
370should be respected whenever possible.
6ee623d5 371
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372=item *
373
374Patches may be applied by the pumpkin holder without the explicit
375cooperation of the module author if and only if they are very minor,
376time-critical in some fashion (such as urgent security fixes), or if
377the module author cannot be reached. Those patches must still be
378given back to the author when possible, and if the author decides on
379an alternate fix in their version, that fix should be strongly
380preferred unless there is a serious problem with it. Any changes not
381endorsed by the author should be marked as such, and the contributor
382of the change acknowledged.
383
384=item *
385
386The version of the module distributed with Perl should, whenever
387possible, be the latest version of the module as distributed by the
388author (the latest non-beta version in the case of public Perl
389releases), although the pumpkin holder may hold off on upgrading the
390version of the module distributed with Perl to the latest version
391until the latest version has had sufficient testing.
392
393=back
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394
395In other words, the author of a module should be considered to have final
396say on modifications to their module whenever possible (bearing in mind
397that it's expected that everyone involved will work together and arrive at
398reasonable compromises when there are disagreements).
399
400As a last resort, however:
401
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402
403If the author's vision of the future of their module is sufficiently
404different from the vision of the pumpkin holder and perl5-porters as a
405whole so as to cause serious problems for Perl, the pumpkin holder may
9a7064ee 406choose to formally fork the version of the module in the Perl core from the
48cb5b3a 407one maintained by the author. This should not be done lightly and
c4f5d98d 408should B<always> if at all possible be done only after direct input
48cb5b3a 409from Larry. If this is done, it must then be made explicit in the
9a7064ee 410module as distributed with the Perl core that it is a forked version and
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411that while it is based on the original author's work, it is no longer
412maintained by them. This must be noted in both the documentation and
413in the comments in the source of the module.
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414
415Again, this should be a last resort only. Ideally, this should never
416happen, and every possible effort at cooperation and compromise should be
417made before doing this. If it does prove necessary to fork a module for
418the overall health of Perl, proper credit must be given to the original
419author in perpetuity and the decision should be constantly re-evaluated to
420see if a remerging of the two branches is possible down the road.
421
422In all dealings with contributed modules, everyone maintaining Perl should
423keep in mind that the code belongs to the original author, that they may
424not be on perl5-porters at any given time, and that a patch is not
425official unless it has been integrated into the author's copy of the
426module. To aid with this, and with points #1, #2, and #3 above, contact
427information for the authors of all contributed modules should be kept with
428the Perl distribution.
429
430Finally, the Perl community as a whole recognizes that respect for
431ownership of code, respect for artistic control, proper credit, and active
432effort to prevent unintentional code skew or communication gaps is vital
433to the health of the community and Perl itself. Members of a community
434should not normally have to resort to rules and laws to deal with each
435other, and this document, although it contains rules so as to be clear, is
436about an attitude and general approach. The first step in any dispute
437should be open communication, respect for opposing views, and an attempt
438at a compromise. In nearly every circumstance nothing more will be
439necessary, and certainly no more drastic measure should be used until
440every avenue of communication and discussion has failed.
3c78fafa 441
70e4a83b 442
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443=head1 DOCUMENTATION
444
445Perl's documentation is an important resource for our users. It's
446incredibly important for Perl's documentation to be reasonably coherent
447and to accurately reflect the current implementation.
448
449Just as P5P collectively maintains the codebase, we collectively
450maintain the documentation. Writing a particular bit of documentation
451doesn't give an author control of the future of that documentation.
452At the same time, just as source code changes should match the style
453of their surrounding blocks, so should documentation changes.
454
455Examples in documentation should be illustrative of the concept
456they're explaining. Sometimes, the best way to show how a
457language feature works is with a small program the reader can
458run without modification. More often, examples will consist
459of a snippet of code containing only the "important" bits.
460The definition of "important" varies from snippet to snippet.
1bb8a155 461Sometimes it's important to declare C<use strict> and C<use warnings>,
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462initialize all variables and fully catch every error condition.
463More often than not, though, those things obscure the lesson
464the example was intended to teach.
465
466As Perl is developed by a global team of volunteers, our
467documentation often contains spellings which look funny
468to I<somebody>. Choice of American/British/Other spellings
469is left as an exercise for the author of each bit of
470documentation. When patching documentation, try to emulate
471the documentation around you, rather than changing the existing
472prose.
473
474In general, documentation should describe what Perl does "now" rather
475than what it used to do. It's perfectly reasonable to include notes
476in documentation about how behaviour has changed from previous releases,
9e9fdd5d 477but, with very few exceptions, documentation isn't "dual-life" --
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478it doesn't need to fully describe how all old versions used to work.
479
480
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481=head1 CREDITS
482
3b4ebcde 483"Social Contract about Contributed Modules" originally by Russ Allbery E<lt>rra@stanford.eduE<gt> and the perl5-porters.
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