ScalafmtConfig: allow fileOverride shortcuts, set cross-build dialects

[kitbellew]

Fixes #2882.

[tgodzik]

Just a minor comments, but otherwise looks super useful!

[tgodzik]

Why not also Scala 3? The convention would be src/main/scala-3

[kitbellew]

scala-3 is a major version. we can't deterministically figure out which specific minor dialect to use, hence automatic dialect is only for minor versions.

are there scala 3.0x already in active use?

[tgodzik]

We started using that convention here: https://github.com/scalameta/metals/tree/main/mtags/src/main/scala-3/scala/meta/internal

It should be less common for users to use scala-3.0 or scala-3.1, but I suppose it could happen. However I don't expect the convention to be different that in Scala 2.

We could default for now to dialect Scala3 for now I think. We will need to update it anyway when some drastic things happen, though 3.1 didn't change anything syntactic still.

[kitbellew]

do you know how sbt cross build determines source directory to use for a given scala version by default? that's the only thing we should realistically support here.

for metals, i found this complex, non-default logic: https://github.com/scalameta/metals/blob/main/build.sbt

[kitbellew]

specifically, I'm looking for scala3 version-specific subdirs like https://www.scala-sbt.org/1.x/docs/Cross-Build.html#Scala-version+specific+source+directory

[kitbellew]

you mean, not just with mtags but any default cross build?

also, if it works, the difference is likely this: sbt knows the dialect it's building, and just needs to find the source directories for it. however, scalafmt is opposite: knows the directory but doesn't know the dialect.

it's easy to determine if from scala-2.13; what should it be for scala-3?

and for this logic (https://www.scala-sbt.org/1.x/docs/Cross-Build.html#Scala-version+specific+source+directory), how will they apply it to scala 3? would it expect scala-3.10 for 3.1.0, or scala-3.1 (since the migration guide says scala3 uses major.minor.patch instead of epoch.major.minir for scala2).

[kitbellew]

ok, found this: sbt/sbt#6424

above the changes, lines 745 and 760, they are reading sources from scalaBinaryVersion. i don't know if default scalaBinaryVersion for dotty is scala-3 or scala-3.1 or scala-3.1.0.

i think right now we can do one of two things:

• add dialect support for scala-3.0 and scala-3.1 as that would allow us to determine the dialect reasonably
• revisit this case later, when we have a better understanding.

what would you prefer, @tgodzik?

[tgodzik]

I checked the default cross build sbt behaviour it recognizes scala-3 directory by default in a sample project. It doesn't work for scala-3.0 etc.

The behaviour in sbt/sbt#6424 was for release candidates that no longer applies.

I think it's safe to assume that scala-3 will always work. Having 3.0 and 3.1 directories is no in the plans AFAIK

[kitbellew]

ok, done. added scala-3.

[tgodzik]

Thanks!