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docs/project/support_policy.pod - Parrot Release and Support Policy

This document describes Parrot's release schedule and support policy.

Parrot's support policy -- for bug reporting, patches, and releases -- relies strongly on its release schedule.

The Parrot team makes twelve releases a year, on the third Tuesday of every month. We make two kinds of releases, "supported" releases and "developer" releases.

The supported releases happen quarterly, with the first release in January, numbered X.0.0, then X.1.0, etc. The X.0, X.3, X.6, and X.9 releases are considered supported, they:

  • Receive update releases for critical bug/security fixes (1.0.1, etc).
  • Have documented deprecations between each supported release.
  • Are intended for distribution packaging.
  • Are intended for users.

The developer releases happen every month between two supported releases. The developer releases:

  • Track the latest monthly feature additions and removals from master
  • Do not receive bug/security releases. (Fixes appear in the next developer or supported release).
  • Are intended for developers.

To allow for healthy growth in the project, in addition to adding new features we will also regularly deprecate features and remove them. To ease the burden of these changes on the users, our policy is to notify users of these deprecations in at least one supported release before removal and to provide users with a reasonable upgrade path. Deprecation notices are listed in the file api.yaml, together with a version number to help us track when the feature is safe to remove. The suggested upgrade paths for deprecated features can be found on the ParrotDeprecations wiki page. Note that deprecation removals that are committed without an appropriate upgrade path are subject to reversion.

For example, if a feature exists in Parrot 2.0 (January 2010), and is not listed for deprecation in that release, the user can be confident that it will still exist at the next supported release, Parrot 2.3 (April 2010).

After a feature is announced as deprecated, it might not appear in the next supported release. We sometimes delay removing deprecated features for various reasons, including dependencies by other parts of the core.

The developer releases have more flexibility in feature removal, while still meeting the deprecation requirements for support releases. A feature that has a deprecation notification in the 2.0 release may be removed from any monthly developer release between 2.0 and the next supported release, though we're likely to stagger the removals.

api.yaml is the definitive source of information about deprecations. If conflicting information is presented on the wiki, in tickets or elsewhere, api.yaml should be considered correct.

HLLs, libraries and other users of Parrot will inevitably find that we deprecate some core features which they depend on. In order to minimize the pain caused by this deprecation and the subsequent "upgrade tax" (i.e. the time users must spend to keep their code working after an upgrade), we now forbid the removal of any deprecated feature until an appropriate upgrade path has been documented. Any deprecated features that are removed without an appropriate notification are subject to reversion until such notifications have been added. The single (rare) exception to this rule is any core feature which is broken or incomplete to the point that it is deemed unusable by any user.

These notifications must be listed on the ParrotDeprecations wiki page, along with ticket numbers, a short summary of the deprecation and the expected impact on users. A longer explanation of each deprecation must be put on a page dedicated to the deprecations for a specific supported release. This page provides a short description of each change, its rationale and at least one example of how affected code can be modified to work after the deprecation takes effect.

The purpose of these notifications is to make life easier for users of Parrot. If an existing feature is incomplete or broken to the degree that no external projects is likely to be able to make use of it, the removal of that feature does not require a documented upgrade path. We expect such deprecations to be very rare.

From time to time, we may add features to get feedback on their utility and design. Marking them as "Experimental" in api.yaml indicates that we may modify or remove them without official deprecation notices. Use them at your own risk--and please provide feedback through official channels if you use them successfully or otherwise.

Internal changes to Parrot which require users to add code in order to continue functioning normally also fall under our support policy. An example of this kind of change is the addition of the generational gc, which required a write barrier on VTABLE functions which modified the contents of a PMC.

We support a version of Parrot by accepting patches and bug reports for that version and by answering questions and helping to explain the code to users and developers. We will do our best to fix all reported bugs, though we triage bugs based on their severity, the difficulty of reproducing them, their platform characteristics, and other criteria. As we are primarily volunteers, we offer no warranty nor guarantee of support other than our pride in producing great software as a community.

For supported releases, we will make additional releases (1.0.1, 1.0.2, etc) to address critical bugs or security problems. What's considered "critical" we'll have to judge on a case-by-case basis, but the users can be confident that bugfix releases will not add or remove features, and we'll work to keep the changes as minimal as possible while resolving the problem.

If you decide to use developer releases to get the latest feature developments, we encourage you to update to each monthly release. If you do encounter a problem, it may have already been fixed in a later supported or developer release.

On the whole, we're happy to support releases as much as a year old. We might even go as far as making a bug/security release for a supported release up to two years old, depending on the circumstances. As a volunteer project we don't have the resources to commit to making bug/security releases farther back than that. Depending on the nature of your problem, it's likely you'll be able to get help from individual volunteers within the project or commercial support organizations, though that help may take the form of helping you upgrade.

If you have received an older release packaged by an operating system vendor or third party, please ask your vendor to get in touch with us, as we're glad to provide them with guidance for the upgrade.

We heartily recommend that you take the initiative to help us help you, by providing useful information about potential bugs and by answering diagnostic questions -- perhaps even trying patches or specific revisions.

In future releases, we might make changes to the bytecode format that would prevent bytecode generated on one supported release from running on a later supported release. These changes will follow our usual deprecation guidelines, with adequate advance notice. We plan to develop tools to migrate between bytecode formats (let us know if you have an urgent need for them), but we generally recommend that you distribute your code in a source form (in the high-level language or PIR), and allow Parrot to generate the bytecode as a local optimization.

We commit to running (passing all tests) on our supported platforms.

We support recent versions of the three major operating system families: GNU/Linux, Mac OS X, and Microsoft Windows. Any version less than two years old counts as "recent".

We support the most recent version of the dominant compiler which conforms to the C89 standard on each supported platform.

We may not support all additional features on every platform (JIT, native binaries, alternate runcores), but the default configuration and runstate of Parrot will work on all supported platforms.

Other platforms and compilers will also be supported, but we can't commit to supporting a platform without at least one champion who has the skills to make portability fixes, and is willing to test the monthly developer releases, or preferably a regular checkout of master. We might not include a platform in our official support list (even with a champion) if supporting that platform would create an undesirable support burden for the other major platforms.

If it has been included in at least one supported release, a backwards-incompatible change requires deprecation:

  • bytecode changes (opcode or core PMC removals, renames)
  • PARROT_API function changes
  • PIR or PASM syntax changes
  • API changes in the compiler tools
  • changes to Parrot that require HLLs or libraries to add code

Please note that these features do not require deprecation notices:

  • Parrot functions not marked with PARROT_API or documented as part of the public API (listed in docs/embed.pod)
  • The layout of Parrot's internal data structures
  • Parrot internals hidden behind a public API
  • Items otherwise eligible but marked as "experimental" in api.yaml

Note that all pointers passed to and returned from functions marked with PARROT_API are considered opaque. We do not guarantee backwards compatibility between monthly releases for the layout of these pointers; dereference them at your own risk.

Before 1.0, version numbers were ad hoc. Our 1.0 release did not occur in January, so no 1.X releases are from the same months as their 2.X counterparts. Also, the frequency of supported releases is not constant over the life of the project. See docs/parrothist.pod for details about which existing releases were considered supported.

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