Compilation error on Scala 3

[NikKozh]

Hi! We are migrating big project from Scala 2 to 3 and we have encountered problem with scalaxb sbt plugin - seems like it generates Scala 2 code, which results in errors like:

[error] 434 |  import Helper._
[error]     |                ^
[error]     |`_` is no longer supported for a wildcard import; use `*` instead
[error]     |This construct can be rewritten automatically under -rewrite -source future-migration.

For some reasons we can't use -rewrite -source flags, but even with them (in separate test project) there is still multiple warnings like:

[warn] 419 |        case that: DataWriter[_] =>
[warn]     |                   ^^^^^^^^^^^^^
[warn]     |                 pattern selector should be an instance of Matchable,,
[warn]     |                 but it has unmatchable type Any instead

Which makes compilation impossible with Xfatal-warnings flag.

From what I saw in this repo, it seems like Scala 3 should be supported, so maybe I am doing something wrong?

There is dependencies I use in build.sbt:

ThisBuild / scalaVersion := "3.4.1"

lazy val scalaXml = "org.scala-lang.modules" %% "scala-xml" % "2.3.0"
lazy val scalaParser = "org.scala-lang.modules" %% "scala-parser-combinators" % "2.4.0"
lazy val jaxb = "javax.xml.bind" % "jaxb-api" % "2.3.1"
lazy val dispatchV = "2.0.0"
lazy val dispatch = "org.dispatchhttp" %% "dispatch-core" % dispatchV

(it's basically last versions for all needed dependencies from docs)

And plugins.sbt:

addSbtPlugin("org.scalaxb"          % "sbt-scalaxb"               % "1.12.2")

I can provide a little example project with reproducible error, if needed. Any help would be appreciated!

[eed3si9n]

#661 I think added tests including Scala 3.x, but I guess I didn't check if the generated code has no warnings.

[NikKozh]

Hi @eed3si9n, I would like to reopen this issue, since on the last version of scalaxb this problem is still presented.

[eed3si9n]

Is it still the same Scala version?

[NikKozh]

Actually no, we switched to the LTS version: 3.3.6

Dependencies:

lazy val dispatchVersion = "2.0.0"
lazy val dispatch = "org.dispatchhttp" %% "dispatch-core" % dispatchVersion
lazy val jaxbApi = "javax.xml.bind" % "jaxb-api" % "2.3.1"
lazy val scalaXml = "org.scala-lang.modules" %% "scala-xml" % "2.4.0"
lazy val scalaParser = "org.scala-lang.modules" %% "scala-parser-combinators" % "2.4.0"

But main point is, I did some experiments, and found out that problem occurs only with -source:future compilation flag. We need it for "better monadic for" functional (https://github.com/oleg-py/better-monadic-for?tab=readme-ov-file#note-on-scala-3), but seems like it enforcing Scala 3 syntax on all source code.

There is could be something to do to make scalaxb and this flag compatible?

[NikKozh]

So there is workaround

We found that using flags -source:future-migration with -rewrite and -Wconf:src=src_managed/.*:silent leads to:

1. Plugin generates code with Scala 3 syntax errors and warnings
2. Compiler automatically rewrites places that give errors
3. And leftover warnings are ignored with the last -Wconf flag

Also future-migration setting allows to keep "better monadic for" functional and, since our project already in Scala 3 syntax, rewrite don't actually rewrites anything else.

With that we now able to use plugin without problems, but it would be ideal ofc if generated code was compatible with -source:future flag as is.