[openssl-project] A proposal for an updated OpenSSL version scheme (v2)

[Tim Hudson]

If you accept that we have a MAJOR.MINOR.FIX.PATCH encoding currently
documented and in place and that the encoding in OPENSSL_VERSION_NUMBER is
documented then the semantic versioning is an easy change.
We do not need to change our encoding of MAJOR.MINOR - that is documented
and fixed. We just need to start using it the way semantic versioning says
we should.
We need to eliminate FIX - there is no such concept in semantic versioning.
And PATCH exists as a concept but in semantic versioning terms it is a
number.

That leads to two main choices in our current encoding as to how we achieve
that:
1) leave old FIX blank
2) move old PATCH to old FIX and leave old PATCH blank (i.e. old FIX is
renamed to new PATCH and old PATCH is eliminated)

Option 2 offers the *least surprise* to users - in that it is how most
users already think of OpenSSL in terms of a stable API - i.e. our current
MAJOR.MINOR.FIX is actually read as MAJOR.MINOR.PATCH or to be more precise
our users see FIX and PATCH as combined things - they don't see our MAJOR
and MINOR as combined things.

Under option 2 it does mean anyone that thinks a change of our current
MINOR means an ABI break would be interpreting things incorrectly - but
that interpretation is *entirely safe* - in that they would be assuming
something more conservative rather than less conservative. And leaving the
old PATCH blank doesn't hurt anyone.

I don't think that moving to semantic versioning requires us to change our
encoding of OPENSSL_VERSION_NUMBER except to move PATCH to FIX - as one of
those concepts disappears.
And then when we do a major release update (like 1.1.1) we end up with a
MAJOR version change.

Alternatively, we can elect to effectively say the OPENSSL_VERSION_NUMBER
encoding we have documented and supported is subject to yet another change
where we reinterpret things.
That is doable - but I also think entirely unnecessary and confusing for
our users.

Tim
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