1PERLPOLICY(1) Perl Programmers Reference Guide PERLPOLICY(1)
2
6 perlpolicy - Various and sundry policies and commitments related to the
7 Perl core
8
10 This document is the master document which records all written policies
11 about how the Perl 5 Porters collectively develop and maintain the Perl
12 core.
13
15 Perl 5 Porters
16 Subscribers to perl5-porters (the porters themselves) come in several
17 flavours. Some are quiet curious lurkers, who rarely pitch in and
18 instead watch the ongoing development to ensure they're forewarned of
19 new changes or features in Perl. Some are representatives of vendors,
20 who are there to make sure that Perl continues to compile and work on
21 their platforms. Some patch any reported bug that they know how to
22 fix, some are actively patching their pet area (threads, Win32, the
23 regexp -engine), while others seem to do nothing but complain. In
24 other words, it's your usual mix of technical people.
25 Over this group of porters presides Larry Wall. He has the final word
27 in what does and does not change in any of the Perl programming
28 languages. These days, Larry spends most of his time on Perl 6, while
29 Perl 5 is shepherded by a "pumpking", a porter responsible for deciding
30 what goes into each release and ensuring that releases happen on a
31 regular basis.
32 Larry sees Perl development along the lines of the US government:
34 there's the Legislature (the porters), the Executive branch (the
35 -pumpking), and the Supreme Court (Larry). The legislature can discuss
36 and submit patches to the executive branch all they like, but the
37 executive branch is free to veto them. Rarely, the Supreme Court will
38 side with the executive branch over the legislature, or the legislature
39 over the executive branch. Mostly, however, the legislature and the
40 executive branch are supposed to get along and work out their
41 differences without impeachment or court cases.
42 You might sometimes see reference to Rule 1 and Rule 2. Larry's power
44 as Supreme Court is expressed in The Rules:
45 1. Larry is always by definition right about how Perl should behave.
47 This means he has final veto power on the core functionality.
48 2. Larry is allowed to change his mind about any matter at a later
50 date, regardless of whether he previously invoked Rule 1.
51 Got that? Larry is always right, even when he was wrong. It's rare to
53 see either Rule exercised, but they are often alluded to.
54
56 Perl 5 is developed by a community, not a corporate entity. Every
57 change contributed to the Perl core is the result of a donation.
58 Typically, these donations are contributions of code or time by
59 individual members of our community. On occasion, these donations come
60 in the form of corporate or organizational sponsorship of a particular
61 individual or project.
62 As a volunteer organization, the commitments we make are heavily
64 dependent on the goodwill and hard work of individuals who have no
65 obligation to contribute to Perl.
66 That being said, we value Perl's stability and security and have long
68 had an unwritten covenant with the broader Perl community to support
69 and maintain releases of Perl.
70 This document codifies the support and maintenance commitments that the
72 Perl community should expect from Perl's developers:
73 · We "officially" support the two most recent stable release series.
75 5.12.x and earlier are now out of support. As of the release of
76 5.18.0, we will "officially" end support for Perl 5.14.x, other
77 than providing security updates as described below.
78 · To the best of our ability, we will attempt to fix critical issues
80 in the two most recent stable 5.x release series. Fixes for the
81 current release series take precedence over fixes for the previous
82 release series.
83 · To the best of our ability, we will provide "critical" security
85 patches / releases for any major version of Perl whose 5.x.0
86 release was within the past three years. We can only commit to
87 providing these for the most recent .y release in any 5.x.y series.
88 · We will not provide security updates or bug fixes for development
90 releases of Perl.
91 · We encourage vendors to ship the most recent supported release of
93 Perl at the time of their code freeze.
94 · As a vendor, you may have a requirement to backport security fixes
96 beyond our 3 year support commitment. We can provide limited
97 support and advice to you as you do so and, where possible will try
98 to apply those patches to the relevant -maint branches in git,
99 though we may or may not choose to make numbered releases or
100 "official" patches available. Contact us at
101 <perl5-security-report@perl.org> to begin that process.
102
104 Our community has a long-held belief that backward-compatibility is a
105 virtue, even when the functionality in question is a design flaw.
106 We would all love to unmake some mistakes we've made over the past
108 decades. Living with every design error we've ever made can lead to
109 painful stagnation. Unwinding our mistakes is very, very difficult.
110 Doing so without actively harming our users is nearly impossible.
111 Lately, ignoring or actively opposing compatibility with earlier
113 versions of Perl has come into vogue. Sometimes, a change is proposed
114 which wants to usurp syntax which previously had another meaning.
115 Sometimes, a change wants to improve previously-crazy semantics.
116 Down this road lies madness.
118 Requiring end-user programmers to change just a few language
120 constructs, even language constructs which no well-educated developer
121 would ever intentionally use is tantamount to saying "you should not
122 upgrade to a new release of Perl unless you have 100% test coverage and
123 can do a full manual audit of your codebase." If we were to have tools
124 capable of reliably upgrading Perl source code from one version of Perl
125 to another, this concern could be significantly mitigated.
126 We want to ensure that Perl continues to grow and flourish in the
128 coming years and decades, but not at the expense of our user community.
129 Existing syntax and semantics should only be marked for destruction in
131 very limited circumstances. If a given language feature's continued
132 inclusion in the language will cause significant harm to the language
133 or prevent us from making needed changes to the runtime, then it may be
134 considered for deprecation.
135 Any language change which breaks backward-compatibility should be able
137 to be enabled or disabled lexically. Unless code at a given scope
138 declares that it wants the new behavior, that new behavior should be
139 disabled. Which backward-incompatible changes are controlled
140 implicitly by a 'use v5.x.y' is a decision which should be made by the
141 pumpking in consultation with the community.
142 When a backward-incompatible change can't be toggled lexically, the
144 decision to change the language must be considered very, very
145 carefully. If it's possible to move the old syntax or semantics out of
146 the core language and into XS-land, that XS module should be enabled by
147 default unless the user declares that they want a newer revision of
148 Perl.
149 Historically, we've held ourselves to a far higher standard than
151 backward-compatibility -- bugward-compatibility. Any accident of
152 implementation or unintentional side-effect of running some bit of code
153 has been considered to be a feature of the language to be defended with
154 the same zeal as any other feature or functionality. No matter how
155 frustrating these unintentional features may be to us as we continue to
156 improve Perl, these unintentional features often deserve our
157 protection. It is very important that existing software written in
158 Perl continue to work correctly. If end-user developers have adopted a
159 bug as a feature, we need to treat it as such.
160 New syntax and semantics which don't break existing language constructs
162 and syntax have a much lower bar. They merely need to prove themselves
163 to be useful, elegant, well designed, and well tested.
164 Terminology
166 To make sure we're talking about the same thing when we discuss the
167 removal of features or functionality from the Perl core, we have
168 specific definitions for a few words and phrases.
169 experimental
171 If something in the Perl core is marked as experimental, we may
172 change its behaviour, deprecate or remove it without notice. While
173 we'll always do our best to smooth the transition path for users of
174 experimental features, you should contact the perl5-porters
175 mailinglist if you find an experimental feature useful and want to
176 help shape its future.
177 deprecated
179 If something in the Perl core is marked as deprecated, we may
180 remove it from the core in the next stable release series, though
181 we may not. As of Perl 5.12, deprecated features and modules warn
182 the user as they're used. If you use a deprecated feature and
183 believe that its removal from the Perl core would be a mistake,
184 please contact the perl5-porters mailinglist and plead your case.
185 We don't deprecate things without a good reason, but sometimes
186 there's a counterargument we haven't considered. Historically, we
187 did not distinguish between "deprecated" and "discouraged"
188 features.
189 discouraged
191 From time to time, we may mark language constructs and features
192 which we consider to have been mistakes as discouraged.
193 Discouraged features aren't candidates for removal in the next
194 major release series, but we may later deprecate them if they're
195 found to stand in the way of a significant improvement to the Perl
196 core.
197 removed
199 Once a feature, construct or module has been marked as deprecated
200 for a stable release cycle, we may remove it from the Perl core.
201 Unsurprisingly, we say we've removed these things.
202
204 · New releases of maint should contain as few changes as possible.
205 If there is any question about whether a given patch might merit
206 inclusion in a maint release, then it almost certainly should not
207 be included.
208 · Portability fixes, such as changes to Configure and the files in
210 hints/ are acceptable. Ports of Perl to a new platform,
211 architecture or OS release that involve changes to the
212 implementation are NOT acceptable.
213 · Acceptable documentation updates are those that correct factual
215 errors, explain significant bugs or deficiencies in the current
216 implementation, or fix broken markup.
217 · Patches that add new warnings or errors or deprecate features are
219 not acceptable.
220 · Patches that fix crashing bugs that do not otherwise change Perl's
222 functionality or negatively impact performance are acceptable.
223 · Patches that fix CVEs or security issues are acceptable, but should
225 be run through the perl5-security-report@perl.org mailing list
226 rather than applied directly.
227 · Patches that fix regressions in perl's behavior relative to
229 previous releases are acceptable.
230 · Updates to dual-life modules should consist of minimal patches to
232 fix crashing or security issues (as above).
233 · Minimal patches that fix platform-specific test failures or
235 installation issues are acceptable. When these changes are made to
236 dual-life modules for which CPAN is canonical, any changes should
237 be coordinated with the upstream author.
238 · New versions of dual-life modules should NOT be imported into
240 maint. Those belong in the next stable series.
241 · Patches that add or remove features are not acceptable.
243 · Patches that break binary compatibility are not acceptable.
245 (Please talk to a pumpking.)
246 Getting changes into a maint branch
248 Historically, only the pumpking cherry-picked changes from bleadperl
249 into maintperl. This has...scaling problems. At the same time,
250 maintenance branches of stable versions of Perl need to be treated with
251 great care. To that end, we're going to try out a new process for
252 maint-5.12.
253 Any committer may cherry-pick any commit from blead to maint-5.12 if
255 they send mail to perl5-porters announcing their intent to cherry-pick
256 a specific commit along with a rationale for doing so and at least two
257 other committers respond to the list giving their assent. (This policy
258 applies to current and former pumpkings, as well as other committers.)
259
261 A Social Contract about Artistic Control
262 What follows is a statement about artistic control, defined as the
263 ability of authors of packages to guide the future of their code and
264 maintain control over their work. It is a recognition that authors
265 should have control over their work, and that it is a responsibility of
266 the rest of the Perl community to ensure that they retain this control.
267 It is an attempt to document the standards to which we, as Perl
268 developers, intend to hold ourselves. It is an attempt to write down
269 rough guidelines about the respect we owe each other as Perl
270 developers.
271 This statement is not a legal contract. This statement is not a legal
273 document in any way, shape, or form. Perl is distributed under the GNU
274 Public License and under the Artistic License; those are the precise
275 legal terms. This statement isn't about the law or licenses. It's
276 about community, mutual respect, trust, and good-faith cooperation.
277 We recognize that the Perl core, defined as the software distributed
279 with the heart of Perl itself, is a joint project on the part of all of
280 us. From time to time, a script, module, or set of modules (hereafter
281 referred to simply as a "module") will prove so widely useful and/or so
282 integral to the correct functioning of Perl itself that it should be
283 distributed with the Perl core. This should never be done without the
284 author's explicit consent, and a clear recognition on all parts that
285 this means the module is being distributed under the same terms as Perl
286 itself. A module author should realize that inclusion of a module into
287 the Perl core will necessarily mean some loss of control over it, since
288 changes may occasionally have to be made on short notice or for
289 consistency with the rest of Perl.
290 Once a module has been included in the Perl core, however, everyone
292 involved in maintaining Perl should be aware that the module is still
293 the property of the original author unless the original author
294 explicitly gives up their ownership of it. In particular:
295 · The version of the module in the Perl core should still be
297 considered the work of the original author. All patches, bug
298 reports, and so forth should be fed back to them. Their
299 development directions should be respected whenever possible.
300 · Patches may be applied by the pumpkin holder without the explicit
302 cooperation of the module author if and only if they are very
303 minor, time-critical in some fashion (such as urgent security
304 fixes), or if the module author cannot be reached. Those patches
305 must still be given back to the author when possible, and if the
306 author decides on an alternate fix in their version, that fix
307 should be strongly preferred unless there is a serious problem with
308 it. Any changes not endorsed by the author should be marked as
309 such, and the contributor of the change acknowledged.
310 · The version of the module distributed with Perl should, whenever
312 possible, be the latest version of the module as distributed by the
313 author (the latest non-beta version in the case of public Perl
314 releases), although the pumpkin holder may hold off on upgrading
315 the version of the module distributed with Perl to the latest
316 version until the latest version has had sufficient testing.
317 In other words, the author of a module should be considered to have
319 final say on modifications to their module whenever possible (bearing
320 in mind that it's expected that everyone involved will work together
321 and arrive at reasonable compromises when there are disagreements).
322 As a last resort, however:
324 If the author's vision of the future of their module is sufficiently
326 different from the vision of the pumpkin holder and perl5-porters as a
327 whole so as to cause serious problems for Perl, the pumpkin holder may
328 choose to formally fork the version of the module in the Perl core from
329 the one maintained by the author. This should not be done lightly and
330 should always if at all possible be done only after direct input from
331 Larry. If this is done, it must then be made explicit in the module as
332 distributed with the Perl core that it is a forked version and that
333 while it is based on the original author's work, it is no longer
334 maintained by them. This must be noted in both the documentation and
335 in the comments in the source of the module.
336 Again, this should be a last resort only. Ideally, this should never
338 happen, and every possible effort at cooperation and compromise should
339 be made before doing this. If it does prove necessary to fork a module
340 for the overall health of Perl, proper credit must be given to the
341 original author in perpetuity and the decision should be constantly re-
342 evaluated to see if a remerging of the two branches is possible down
343 the road.
344 In all dealings with contributed modules, everyone maintaining Perl
346 should keep in mind that the code belongs to the original author, that
347 they may not be on perl5-porters at any given time, and that a patch is
348 not official unless it has been integrated into the author's copy of
349 the module. To aid with this, and with points #1, #2, and #3 above,
350 contact information for the authors of all contributed modules should
351 be kept with the Perl distribution.
352 Finally, the Perl community as a whole recognizes that respect for
354 ownership of code, respect for artistic control, proper credit, and
355 active effort to prevent unintentional code skew or communication gaps
356 is vital to the health of the community and Perl itself. Members of a
357 community should not normally have to resort to rules and laws to deal
358 with each other, and this document, although it contains rules so as to
359 be clear, is about an attitude and general approach. The first step in
360 any dispute should be open communication, respect for opposing views,
361 and an attempt at a compromise. In nearly every circumstance nothing
362 more will be necessary, and certainly no more drastic measure should be
363 used until every avenue of communication and discussion has failed.
364
366 Perl's documentation is an important resource for our users. It's
367 incredibly important for Perl's documentation to be reasonably coherent
368 and to accurately reflect the current implementation.
369 Just as P5P collectively maintains the codebase, we collectively
371 maintain the documentation. Writing a particular bit of documentation
372 doesn't give an author control of the future of that documentation. At
373 the same time, just as source code changes should match the style of
374 their surrounding blocks, so should documentation changes.
375 Examples in documentation should be illustrative of the concept they're
377 explaining. Sometimes, the best way to show how a language feature
378 works is with a small program the reader can run without modification.
379 More often, examples will consist of a snippet of code containing only
380 the "important" bits. The definition of "important" varies from
381 snippet to snippet. Sometimes it's important to declare "use strict"
382 and "use warnings", initialize all variables and fully catch every
383 error condition. More often than not, though, those things obscure the
384 lesson the example was intended to teach.
385 As Perl is developed by a global team of volunteers, our documentation
387 often contains spellings which look funny to somebody. Choice of
388 American/British/Other spellings is left as an exercise for the author
389 of each bit of documentation. When patching documentation, try to
390 emulate the documentation around you, rather than changing the existing
391 prose.
392 In general, documentation should describe what Perl does "now" rather
394 than what it used to do. It's perfectly reasonable to include notes in
395 documentation about how behaviour has changed from previous releases,
396 but, with very few exceptions, documentation isn't "dual-life" -- it
397 doesn't need to fully describe how all old versions used to work.
398
400 "Social Contract about Contributed Modules" originally by Russ Allbery
401 <rra@stanford.edu> and the perl5-porters.
402perl v5.16.3 2013-03-04 PERLPOLICY(1)