Add reflect TypeRef.underlying

Fixes #15799

Author: nicolasstucki

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -1841,6 +1841,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       extension (self: TypeRef)
         def isOpaqueAlias: Boolean = self.symbol.isOpaqueAlias
         def translucentSuperType: TypeRepr = self.translucentSuperType
+        def underlying: TypeRepr = self.underlying
       end extension
     end TypeRefMethods
 

library/src/scala/quoted/Quotes.scala

@@ -2766,6 +2766,9 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
       extension (self: TypeRef)
         def isOpaqueAlias: Boolean
         def translucentSuperType: TypeRepr
+        /** The type bounds of the referenced type. */
+        @experimental
+        def underlying: TypeRepr
       end extension
     end TypeRefMethods
 

tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala

@@ -65,8 +65,10 @@ val experimentalDefinitionInLibrary = Set(
   //// New feature: Macro annotations
   "scala.annotation.MacroAnnotation",
 
-   //// New APIs: Quotes
-  // Can be stabilized in 3.3.0 (unsure) or later
+  //// New APIs: Quotes
+  // Can be stabilized in 3.4.0 or later
+  "scala.quoted.Quotes.reflectModule.TypeRefMethods.underlying",
+  // Can be stabilized in 3.4.0 (unsure) or later
   "scala.quoted.Quotes.reflectModule.CompilationInfoModule.XmacroSettings",
   "scala.quoted.Quotes.reflectModule.FlagsModule.JavaAnnotation",
   // Cant be stabilized yet.

tests/run-macros/i15799.check

@@ -0,0 +1,7 @@
+Alias: (X.Alias,_ >: scala.Predef.String <: scala.Predef.String)
+Opaque: (X.Opaque,_ >: scala.Nothing <: scala.Any)
+Bound: (X.Bound,_ >: scala.Nothing <: scala.Predef.String)
+OpaqueBound: (X.OpaqueBound,_ >: scala.Nothing <: scala.Predef.String)
+Param T: (T,_ >: scala.Nothing <: scala.Any)
+Param U: (U,_ >: scala.Nothing <: scala.Predef.String)
+Param V: (V,_ >: scala.Int <: scala.Any)

tests/run-macros/i15799/Macro_1.scala

@@ -0,0 +1,14 @@
+import scala.quoted.*
+
+object exampleMacro {
+
+  inline def typeDefRhs[T <: AnyKind]: (String, String) = ${ typeDefRhsImpl[T] }
+
+  def typeDefRhsImpl[T <: AnyKind: Type](using Quotes): Expr[(String, String)] = {
+    import quotes.reflect.*
+    val underlyingTpe =
+      TypeRepr.of[T] match
+        case tpe: TypeRef => tpe.underlying
+    Expr((Type.show[T], underlyingTpe.show))
+  }
+}

tests/run-macros/i15799/Test_2.scala

@@ -0,0 +1,21 @@
+@main def Test = {
+  object X {
+    type Alias = String
+    opaque type Opaque = String
+    type Bound <: String
+    opaque type OpaqueBound <: String = String
+  }
+  import X.*
+
+  println(s"Alias: ${exampleMacro.typeDefRhs[Alias]}")
+  println(s"Opaque: ${exampleMacro.typeDefRhs[Opaque]}")
+  println(s"Bound: ${exampleMacro.typeDefRhs[Bound]}")
+  println(s"OpaqueBound: ${exampleMacro.typeDefRhs[OpaqueBound]}")
+
+  def testParams[T, U <: String, V >: Int](x: Int): Unit =
+    println(s"Param T: ${exampleMacro.typeDefRhs[T]}")
+    println(s"Param U: ${exampleMacro.typeDefRhs[U]}")
+    println(s"Param V: ${exampleMacro.typeDefRhs[V]}")
+
+  testParams(3)
+}