Scala 3 support

[pjfanning]

Is your feature request related to a problem? Please describe.

I'm not really a Finagle user but maintain jackson-module-scala. Finagle does not yet support Scala 3 but many of its dependencies do. I'm just opening this issue for discussion purposes.

A few twitter util jars are not supported - see twitter/util#274 (comment)

For Scala 3, this class will need to change to use jackson-module-scala ClassTagExtensions instead of ScalaObjectMapper.

https://github.com/twitter/finagle/blob/develop/finagle-mysql/src/main/scala/com/twitter/finagle/mysql/Value.scala

In theory, you could keep using ScalaObjectMapper for Scala 2 builds. This class is deprecated but there are no plans to remove it from jackson-module-scala 2.x (but it will probably not be part of jackson-module-scala 3.x - the v3.x release is not yet planned and is not worth worrying about yet).

Describe the solution you'd like

Generally, it would be nice to get everyone onto Scala 3.

[ghost]

scala 3 is good so far indeed

[hartmut27]

a cross compile works with Finagle and Scala 3, with the help of ... CrossVersion.for3Use2_13.

build.sbt:

libraryDependencies += "com.twitter" %% "util-core" % "22.12.0" cross CrossVersion.for3Use2_13,
libraryDependencies += "com.twitter" %% "finagle-http" % "22.12.0" cross CrossVersion.for3Use2_13,
libraryDependencies += "com.twitter" %% "finagle-core" % "22.12.0" cross CrossVersion.for3Use2_13,

to identify all transitive dependencies and their versions, this can help

$ sbt dependencyTree

[xin301x]

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