Switch jdk8u development to Git/Skara

[erik.joelsson at oracle.com]

Hello,

Back in February there was a discussion about moving the OpenJDK 8u 
development to Git/Skara together with the jdk11u move [1]. The 
conclusion then, as I understood it, was to wait until sometime after 
jdk11u was moved to give people a chance to get familiar with the new 
development process and iron out the details on how it should be 
applied. The jdk11u move took place over the summer, so I thought now 
would be a good time to revisit the discussion for jdk8u.

The move for 8u is a bit trickier than 11u as a necessary pre step is to 
first consolidate the Mercurial repositories into one, like we did for 
JDK 10. I have already produced a prototype conversion during the 
previous discussion [2], but it's quite outdated at this time. 
Unfortunately, the consolidation process is not easily automated and 
only incremental to a point (basically on a per promotion tag level, but 
even that comes with some caveats in the update world where multiple 
releases are are being developed in parallel). Because of this it's not 
feasible to setup a live mirror like we did for jdk11u. Instead, we will 
need to plan for up to a week (worst case) of downtime where I produce 
the final consolidated HG repository, and then let Skara convert and 
publish this to Github. Ideally it should only take 1-2 days, but these 
consolidations have been finicky in the past, so better plan for the worst.

Another option would be to transition in 2 steps, first to a 
consolidated HG repo, then to Git. This certainly has other drawbacks, 
having to adjust to and support another development process for a short 
period of time. It would, however, make the final transition to Git much 
smoother and similar to the jdk11u transition.

I would like to hear from the maintainers of jdk8u what your preferred 
strategy would be and what timelines that would make sense to you.

/Erik

[1] 
https://mail.openjdk.java.net/pipermail/jdk8u-dev/2021-February/013402.html
[2] https://github.com/openjdk/jdk8u