Sbt version revert to 1.2.8

[poslegm]

Unfortunately we can't update sbt version without breaking compatibility.
sbt-scalafmt v2.2.0 can't work in projects with sbt v1.2.x and older because sbt 1.3.x isn't compatible with sbt 1.2.x.

So I think we should stay on 1.2.8 as long as possible 😞

[tanishiking]

LGTM! Thank you for fixing it sbt/sbt#5049
I gonna kick start sbt-scalafmt 2.2.1 after CI passed

[dwijnand]

sbt 1.3.x isn't compatible with sbt 1.2.x

To be clear: sbt 1.3.x is compatible with sbt 1.2.x, the way "compatible" is normally meant: backwards binary compatible. The compatibility you refer to is forward compatibility: sbt 1.2.x isn't forwards binary compatible with plugins built with sbt 1.3.x.

This isn't new: like all projects new APIs are introduced in new minor versions, making the released version non-forward compatible (scala-library is the exception here, to the detriment of its evolution outside of internal implementation details). What's new is there was a specific change in sbt 1.3 that made it extremely easy to trigger (adding an implicit to the sbt package object).

[anilkumarmyla]

Interested to know which projects are still behind on sbt 1.2.x that require this downgrade? I think in the best of interest as a community we should ensure everyone uses the latest software. A lot of work goes into improving a software and releasing a version that is much better than the previous one (in this case sbt-1.3.x). Bumping sbt version to 1.3.x in all the community plugins is a sure way to organically increase this adoption.

Another way is to build the plugin with both sbt-1.2.x & sbt-1.3.x and publish with only one of them or both (in versions that differ in major/minor versions)

[poslegm]

@anilkumarmyla There are a lot projects with sbt 1.2.x and older :)

I agree that we should motivate community to upgrade their software. But in my opinion 400 LOC formatting plugin shouldn't force users to update entire build system.

There is a possibility to update sbt for us without breaking compatibility sbt/sbt#5049 (comment). I will try to do it.

[dwijnand]

But in my opinion 400 LOC formatting plugin shouldn't force users to update entire build system.

Updating sbt version isn't hard. Users that can't do that can equally stay on older versions of this plugin.

[solarmosaic-kflorence]

FWIW I think it's pretty reasonable to force SBT upgrades when doing major version updates on plugins.