Mill1x support

[yisraelU]

In effort to target Mill 1.x , we need to support Scala 3 in the codegen module which must also support Scala 2.12 .

A bunch of syntax changes were made to be compatible with Scala 3 .
VarArgs expansion is the only syntax that was not supported in Scala 2 , and therefore a config was added to silence the warning in the Scalac options

• Updated changelog

[Copilot]

Pull request overview

This PR adds support for Mill 1.x build tool alongside existing Mill 0.11 and 0.12 support. It introduces platform-specific configurations to handle differences between Mill versions, particularly addressing Scala version requirements (Mill 1.x uses Scala 3.8.1 vs Scala 2.13 for legacy versions) and dependency management challenges. The changes also include Scala 3 compatibility improvements in the codegen module, updating type casting patterns and compiler options to work with newer Scala 3 versions, and refactoring string literal rendering to avoid scala-reflect dependency.

Changes:

• Introduced MillPlatformConfig abstraction to handle version-specific Mill configurations including Scala versions, dependencies, and conflict resolution settings
• Added Mill 1.x support with Scala 3.8.1, new mill-libs dependency, and classpath conflict suppression
• Updated Scala 3 compiler options to support both 3.3.x (-Ykind-projector, -release 8) and 3.8.x (-Xkind-projector, -release 17, -Werror) versions
• Refactored string literal rendering in codegen to use manual escaping instead of scala-reflect for Scala 3 compatibility
• Added Mill 1.x specific source files with updated Mill API usage and test implementations

Reviewed changes

Copilot reviewed 13 out of 17 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
project/Smithy4sBuildPlugin.scala	Introduces MillPlatformConfig abstraction and Mill 1.x support with platform-specific settings
project/Dependencies.scala	Adds Mill 1.x mill-libs dependency with necessary exclusions
modules/mill-codegen-plugin/src-mill-1/smithy4s/codegen/mill/Smithy4sModule.scala	Mill 1.x implementation of Smithy4s codegen plugin with updated Mill API
modules/mill-codegen-plugin/src-mill-1/smithy4s/codegen/LSP.scala	Mill 1.x LSP configuration module using new Mill API
modules/mill-codegen-plugin/test/src-mill-1/smithy4s/codegen/mill/Smithy4sModuleSpec.scala	Comprehensive test suite for Mill 1.x plugin functionality
modules/mill-codegen-plugin/test/src-mill-1/smithy4s/codegen/mill/SmithyLSPConfigSpec.scala	Tests for LSP configuration generation in Mill 1.x
modules/mill-codegen-plugin/src-mill-shared/smithy4s/codegen/mill/Smithy4sModuleCommon.scala	Simplified type matching using pattern matching instead of asInstanceOf
modules/codegen/src/smithy4s/codegen/internals/Renderer.scala	Refactored string literal rendering to use custom escaping for Scala 3 compatibility
modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala	Added Scala 3-compatible type casting with @SuppressWarnings and @unchecked annotations
modules/codegen/src/smithy4s/codegen/transformers/ValidatedNewtypesTransformer.scala	Updated type casting pattern for Scala 3 compatibility
modules/codegen/src-3/smithy4s/codegen/internal/MapTypeCompanionPlatform.scala	New Scala 3-specific platform code for Map type companion
modules/codegen/test/src/smithy4s/codegen/internals/ScaladocSpec.scala	Removed unused empty statement
build.sbt	Updated codegen module to support Scala 3 and Mill Scala 3 versions with appropriate dependencies
modules/bootstrapped/src/generated/...	Updated generated code with improved string escaping (contractions properly escaped)

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[yisraelU]

we used to escape a single quote , which was not necessary

[yisraelU]

ditto

[yisraelU]

ditto

[yisraelU]

same as scala 2 , just for cross compilation purposes

[yisraelU]

This replaced the Scala 2 version of storing source code string literals without using reflection.

[yisraelU]

Since sbt-projectmatrix uses exact Scala version matching for .dependsOn(), the Mill 1.x row (3.8.1) can't find a matching codegen row (3.3.6).
To work around this, millPlatforms now accepts project matrix dependencies explicitly and wires them per-row using depScalaVersion

[lewisjkl]

Looks great, I think we should also update the documentation mill example to show how to setup for mill 1.x now as well

[rochala]

This could be simplified by migrating away from Aux pattern of Primitive to normal parameterized trait like:

private[internals] sealed trait Primitive[T]
private[internals] object Primitive {
  case object Unit extends Primitive[Unit]
  case object Blob extends Primitive[Array[Byte]]

Then Scala 3 typechecker will be satisfied with

  private def renderPrimitive[T](prim: Primitive[T]): T => Line =
    prim match {
      case Primitive.BigDecimal =>
        bd => line"scala.math.BigDecimal(${bd.toString})"
      case Primitive.BigInteger => bi => line"scala.math.BigInt(${bi.toString})"
      case Primitive.Unit       => _ => line"()"
      case Primitive.Double     => t => line"${t.toString}d"
      case Primitive.Float      => t => line"${t.toString}f"
      case Primitive.Long       => t => line"${t.toString}L"
      case Primitive.Int        => t => line"${t.toString}"
      case Primitive.Short      => t => line"${t.toString}"
      case Primitive.Bool       => t => line"${t.toString}"
      case Primitive.Uuid       => uuid => line"java.util.UUID.fromString(${renderStringLiteral(uuid.toString)})"
      case Primitive.String     => s => renderStringLiteral(s)
      case Primitive.Byte       => b => line"${b.toString}"
      case Primitive.Blob =>
        ba =>
          val blob = NameRef("smithy4s", "Blob")
          if (ba.isEmpty) line"$blob.empty"
          else
            line"$blob(Array[Byte](${ba.mkString(", ")}))"
      case Primitive.Timestamp =>
        ts => line"${NameRef("smithy4s", "Timestamp")}(${ts.getEpochSecond()}L, ${ts.getNano()})"
      case Primitive.Document => renderNodeToLine(_)
      case Primitive.Nothing  => v => (v: Nothing)
    }

But confirm me here, I may be wrong why Aux pattern was used here in the first place.

[lewisjkl]

Thanks for the input. Yeah it might be possible to move this direction, I'm not entirely sure. The reason it was done with Aux originally iirc has to do with the usage of recursion schemes in SmithyToIr

smithy4s/modules/codegen/src/smithy4s/codegen/internals/SmithyToIR.scala

Line 1400 in ec25ae8

private def unfoldNodeAndType(layer: NodeAndType): TypedNode[NodeAndType] =

and TypedNode. So I think it would be a larger refactor if we didn't have a GADT for primitive

[lewisjkl]

We can leave the PR open for the weekend in case anyone else wants to review, but I think it's good to go 🎉