Legacy Mill support

[AnthonyGrod]

Hello, I'm a part of the Scala team in IntelliJ and I'm developing a new Mill support under BSP plugin. I'm wondering if we should still support Legacy Mill versions e.g. <= 0.8.0?

[lihaoyi]

IMO I think supporting the last two major versions should be enough, so 0.11.x and 0.12.x for now. Notably, publishing to maven central is broken in older versions due to a change in the maven central API error handling behavior, so any OSS libraries on older versions can't be published anyway

[lefou]

There are more projects in the wild than just the visible open source projects. E.g. I still freelance for projects where Mill is used and we need to switch to years old maintenance branches sometime (in which older Mill versions are used) to change minor stuff and cut new releases. And we like to be able to use IntelliJ. In these projects, nobody releases to Maven Central, so I think that argument doesn't count.

Beside that, I think versions older than 0.10.x don't have proper BSP support (and most likely use GenIdea) so no point in supporting them (via BSP at least) if it calls for extra work.