Inline match on regular expression fails or can't be reduced

[DenisNovac]

Compiler version

"3.0.0-RC2"

Minimized code

inline def showLabel(label: String): Unit = {
    val suggestRegex: Regex = "(Type)([a-zA-Z]+)(Mapping)([a-zA-Z]+)".r
    val docRegex: Regex = "(Test)(Mapping)([a-zA-Z]+)".r
    val simpleRegex: Regex = "([a-zA-Z]+)(Mapping)([a-zA-Z]+)".r

    inline label match {
      case docRegex(doc, _, _) =>
        println(doc)

      case suggestRegex(suggest, suggestType, _, _) =>
        println(suggest)

      case simpleRegex(docType, _, _) =>
        println(docType)

      case _ => throw new Error(s"Error on label: $label")
    }
  }

  showLabel("TestMappingDocument")
  showLabel("sdofjsdifj")

Output

Exception in thread "main" java.lang.Error: Error on label: TestMappingDocument
	at E009_ExampleRegex$.<clinit>(E009_ExampleRegex.scala:34)
	at E009_ExampleRegex.main(E009_ExampleRegex.scala)

Without the last case:

cannot reduce inline match with
 scrutinee:  "TestMappingDocument" : ("TestMappingDocument" : String)
 patterns :  case docRegex(doc @ _, _, _)
             case suggestRegex(suggest @ _, suggestType @ _, _, _)
             case simpleRegex(docType @ _, _, _)

Expectation

I found this example in docs: https://dotty.epfl.ch/docs/reference/metaprogramming/inline.html#inline-matches . It seems that it should fail because of second entry in compile time but it fails on the first one.

[nicolasstucki]

Reducing on arbitrary code is quite difficult. Here we would need an interpreter that know how to evaluate val suggestRegex: Regex = "(Type)([a-zA-Z]+)(Mapping)([a-zA-Z]+)".r and then interpret it's use in a pattern. Note that the inline pattern does not know statically what the pattern is. Therefore this kind of code will most likely never be supported using inline match.

On the other hand, we already trivially support this using quoted code.

import scala.quoted.*
import scala.util.matching.Regex

inline def showLabel(inline label: String): String =
  ${ showLabelExpr('label) }


private def showLabelExpr(label: Expr[String])(using Quotes): Expr[String] = {
  val suggestRegex: Regex = "(Type)([a-zA-Z]+)(Mapping)([a-zA-Z]+)".r
  val docRegex: Regex = "(Test)(Mapping)([a-zA-Z]+)".r
  val simpleRegex: Regex = "([a-zA-Z]+)(Mapping)([a-zA-Z]+)".r

  label.value match {
    case Some(docRegex(doc, _, _)) =>
      Expr(doc)

    case Some(suggestRegex(suggest, suggestType, _, _)) =>
      Expr(suggest)

    case Some(simpleRegex(docType, _, _)) =>
      Expr(docType)

    case Some(value) =>
      quotes.reflect.report.throwError(s"No label matched: $value")

    case None =>
      quotes.reflect.report.throwError(s"Expected label to be a know string but was: ${label.show}")
  }
}

@main def test(): Unit =
  println(showLabel("TestMappingDocument"))
  println(showLabel("sdofjsdifj"))