Timetable for dropping Scala 2.10 support

[SethTisue]

@eed3si9n have you given this any thought yet? might it be fair game for 1.7? or not until 2.0?

my observation is that it is now quite rare for any Scala OSS projects to still have 2.10 in their crossbuilds, and it's exceedingly rare for anyone to bring up 2.10 in a Scala forum or chat room

I don't have a terribly specific motivation for asking, it just seems like anything we can do to drop crufty backwards-compat stuff in the source code and slim the CI matrix down is likely to speed all development work at least somewhat. we could also cut back on warnings noise (currently there is a great deal)

wasn't sure whether to open this in sbt/sbt or sbt/zinc; starting here since this repo is my main concern currently, but you could move it to sbt/sbt if you like

[eed3si9n]

I am not sure. According to Jet Brains' Scala Programming - The State of Developer, which is likely impartial, 61% of the respondents regularly use 2.13, 50% 2.12, 22% 2.11, and 3% 2.10 or older. If we believe the denominator to be representative enough, and overall ecosystem to be large enough, 3% could be thousands of users, if not tens of thousands of users.

Anecdotally, I've heard from someone during the whole log4shell days that they were unaffected by it because many of their builds at work (a major company) are still on sbt 0.13. If so that could explain some portion of the users who are regularly using Scala 2.10, but I really don't know. Maybe they are just ok with 2.10, and are not interested in upgrading various libraries. If they are semi-permanently using sbt 0.13, I guess then sbt 2.x could drop Scala 2.10 and it would be ok, but maybe some other portion of the users are using the latest JDK, latest sbt, but retro Scala.

[SethTisue]

I'm content to give up on seeing 2.10 dropped in sbt 1.x, but I still think it should be dropped in sbt 2.x 🔪 In the interest of slimming down our own collective development effort