Type-safe compilation with Scala 3 and macros

Validate.scala

// Oto Brglez - <otobrglez@gmail.com> - Jul 2026
import scala.annotation.StaticAnnotation, scala.quoted.*

final case class range(val lo: Int, val hi: Int) extends StaticAnnotation

object Validate:
  inline def validate[T](inline o: T): Unit = ${ validateI[T]('o) }
  
  private def validateI[T: Type](o: Expr[T])(using Quotes): Expr[Unit] =
    import quotes.reflect.*
    val rangeT = TypeRepr.of[range]
    val params = TypeRepr.of[T].typeSymbol.primaryConstructor.paramSymss.flatten.filter(!_.isType)

    o.asTerm.underlyingArgument match
      case Apply(Select(_, "apply"), args) =>
        params.zip(args).foreach: (p, arg) =>
          val bounds = p.annotations.collectFirst:
            case Apply(Select(New(tt), _), List(Literal(IntConstant(lo)), Literal(IntConstant(hi))))
              if tt.tpe =:= rangeT => lo -> hi
          
          bounds -> arg match
            case Some(lo -> hi) -> Literal(IntConstant(v)) if v < lo || v > hi =>
              report.errorAndAbort(s"${p.name} = $v is outside [$lo, $hi]", arg.pos)
            case _ => ()
      case _ => report.errorAndAbort("tsValidate requires construction.")

    '{ () }

// Demo (separate file)
final case class Config(
  @range(1, 65_535) port: Int,
  @range(1, 256) maxThreads: Int,
  @range(100, 30_000) timeoutMs: Int
)

@main def demoApp: Unit =
  import Validate.*
  validate(Config(port = 1, maxThreads = 10, timeoutMs = 3233))
  validate(Config(port = -12, maxThreads = 10, timeoutMs = 3233))

// Compile-time explosion:
// scala-cli run Validate.scala TSValidationApp.scala --server=false
// Warning: setting /Users/oto/Projects/scala-sandbox as the project root directory for this run.
// -- Error: /Users/oto/Projects/scala-sandbox/TSValidationApp.scala:13:25 --------
// 13 |  validate(Config(port = -12, maxThreads = 10, timeoutMs = 3233))
//    |                         ^^^
//    |                         port = -12 is outside [1, 65535]
// 1 error found
// Compilation failed