Add quotes.Type.valueOfConstant

With quote pattern matching it is possible to match over the structure of a type, this add to possility to extract the values from constant types.

This is esential to provide handle `Mirror.{MirroredLabel, MirroredElemLabels}` witthout needing reflection.

Author: nicolasstucki

library/src-bootstrapped/scala/quoted/Type.scala

@@ -13,11 +13,31 @@ object Type:
 
   /** Show a source code like representation of this type without syntax highlight */
   def show[T <: AnyKind](using Type[T])(using Quotes): String =
-    import quotes.reflect._
+    import quotes.reflect.*
     TypeTree.of[T].show
 
   /** Return a quoted.Type with the given type */
   @compileTimeOnly("Reference to `scala.quoted.Type.of` was not handled by PickleQuotes")
   given of[T <: AnyKind](using Quotes): Type[T] = ???
 
+
+  /** Extracts the value of singleton constant type, None otherwise.
+   *
+   *  Example usage:
+   *  ```scala
+   *  ... match
+   *    case '{ $mirrorExpr : Mirror.Sum { type MirroredLabel = label } } =>
+   *      Type.valueOfConstant[label] // Option[String]
+   *  }
+   *  ```
+   *  @syntax markdown
+   */
+  def valueOfConstant[T](using Type[T])(using Quotes): Option[T] =
+    import quotes.reflect.*
+    def valueOf(tpe: TypeRepr): Option[T] =
+      tpe.dealias.widenTermRefByName match
+        case ConstantType(const) => Some(const.value.asInstanceOf[T])
+        case _ => None
+    valueOf(TypeRepr.of[T])
+
 end Type

tests/run-macros/from-type.check

@@ -0,0 +1,25 @@
+Some(true)
+Some(false)
+Some(1)
+Some(2)
+Some(3)
+Some(4)
+Some(5)
+Some(6.0)
+Some(7.0)
+Some(a)
+Some(abc)
+Some(10)
+Some(11)
+None
+None
+None
+None
+None
+None
+None
+None
+None
+None
+None
+None

tests/run-macros/from-type/Macro_1.scala

@@ -0,0 +1,8 @@
+import scala.quoted.*
+
+inline def testValueOfType[T]: Unit = ${ testValueOfTypeExpr[T] }
+
+private def testValueOfTypeExpr[T: Type](using Quotes): Expr[Unit] =
+  val value = Type.valueOfConstant[T]
+  val strExpr = Expr(value.toString)
+  '{ println($strExpr) }

tests/run-macros/from-type/Test_2.scala

@@ -0,0 +1,34 @@
+
+@main def Test: Unit =
+  testValueOfType[true]
+  testValueOfType[false]
+  testValueOfByte[1]
+  testValueOfShort[2]
+  testValueOfType[3]
+  testValueOfType[4]
+  testValueOfType[5L]
+  testValueOfType[6d]
+  testValueOfType[7f]
+  testValueOfType['a']
+  testValueOfType["abc"]
+  val x: 10 = 10
+  testValueOfType[x.type]
+  type A = 11
+  testValueOfType[A]
+
+
+  testValueOfType[Boolean]
+  testValueOfType[Byte]
+  testValueOfType[Short]
+  testValueOfType[Int]
+  testValueOfType[Long]
+  testValueOfType[Double]
+  testValueOfType[Float]
+  testValueOfType[Char]
+  testValueOfType[String]
+  testValueOfType[Null]
+  testValueOfType[Any]
+  testValueOfType[Some[1]]
+
+transparent inline def testValueOfByte[B <: Byte] = testValueOfType[B]
+transparent inline def testValueOfShort[S <: Short] = testValueOfType[S]