[ruby-core:56878] [ruby-trunk - misc #8835][Open] Introducing a semantic versioning scheme and branching policy

Issue #8835 has been reported by knu (Akinori MUSHA).

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misc #8835: Introducing a semantic versioning scheme and branching policy
https://bugs.ruby-lang.org/issues/8835

Author: knu (Akinori MUSHA)
Status: Open
Priority: Normal
Assignee: nobu (Nobuyoshi Nakada)
Category: misc
Target version: current: 2.1.0


=begin
[This is a presentation for ((<DevelopersMeeting20130831Japan|URL:https://bugs.ruby-lang.org/projects/ruby/wiki/DevelopersMeeting20130831Japan>)).]


Ruby's versioning scheme is currently not well defined or well
utilized.

First, RUBY_API_VERSION was introduced in 1.9.1, but has not been
properly maintained since then.  There must have been at least a few
ABI incompatible changes (although we tried hard to keep source level
compatibility) and many API additions between 1.9.1 and 1.9.3, but
RUBY_API_VERSION was never bumped.

Secondly, it looks like TEENY version is fixed to zero in the 2.x
series without being used effectively.  We often find overlooked
incompatibility or feature bugs after an official release x.y.0, and
would like to fix them in a backward compatible way.  I'd suggest we
accept such a situation will happen, and bump TEENY when such a fix
that affects forward compatibility is made.  We have up to nine times
of chance for fixing such a situation, and shouldn't be too worried
about running out of digits.

So, here I propose introducing a new versioning scheme as follows,
much with Semantic Versioning (http://semver.org/) in mind:

(1) From 2.1.0 and on, RUBY_API_VERSION shall match RUBY_VERSION.

    Giving them different numbers has been a source of confusion, and
    introducing this scheme is a way to provide RUBY_VERSION with how to
    read API compatibility from the numbers.

(2) MINOR version is incremented when an incompatible API change is
    made.

    In practice, it is incremented before a change to break
    compatibility is actually made.  When a relatively significant
    amount of change is going to be made, which would break
    compatibility, or hurts stability for a certain period of time.

    Before making such a change, a new stable branch
    ruby_{MAJOR}_{MINOR} is cut off from trunk, and MINOR version is
    bumped on trunk.  MAJOR version may be incremented instead,
    resetting MINOR to zero.

    On the ruby_{MAJOR}_{MINOR} branch, when the time comes for
    prereleasing {MAJOR}.{MINOR}.0, a new branch
    ruby_{MAJOR}_{MINOR}_0 is cut off from the ruby_{MAJOR}_{MINOR}
    branch.

(3) TEENY version is incremented when functionality is added in a
    backward-compatible manner.

    It happens on ruby_{MAJOR}_{MINOR} branches, where a new branch
    ruby_{MAJOR}_{MINOR}_{TEENY} is cut off when it is released,
    resetting PATCHLEVEL to zero.
 
(4) PATCHLEVEL is initialized to zero on each
    ruby_{MAJOR}_{MINOR}_{TEENY} branch where TEENY > 0 on creation,
    and incremented every time a change is made on the branch.

    On a ruby_{MAJOR}_{MINOR}_0 branch, PATCHLEVEL is kept at -1
    during the prerelease period.  It is set to zero when
    {MAJOR}.{MINOR}.0 is officially released.

    On other branches, it is fixed to -1.

Note that MINOR and TEENY need not be bumped every time an applicable
change is made, but once before a new official release is rolled out
from the branch.

With this scheme introduced, version specific library subdirectory
names only need to have {MAJOR}.{MINOR} in it, and user can safely
upgrade ruby to a new teeny version without having to rebuild and
reinstall already installed libraries.

[Figure: Branch Tree]

    --o-----------------------o----------(trunk)
       \                       \
        o--o--o--o--(ruby_2_1)  o--o--...--(ruby_2_2)
            \  \  \                 \
             \  \  \                 o--[v2_2_0_0]--...--(ruby_2_2_0)
              \  \  \
               \  \  o--[v2_1_2_0]--[v2_1_2_ppp]--...--(ruby_2_1_2)
                \  \
                 \  o--[v2_1_1_0]--[v2_1_1_ppp]--...--(ruby_2_1_1)
                  \
                   o--[v2_1_0_0]--[v2_1_0_ppp]--...--(ruby_2_1_0)
=end



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