From 984a9c4e341ccf51da6f327fc80ae8cdb8475286 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Mon, 23 Jan 2023 09:56:08 +0100
Subject: [PATCH] Add reflect `TypeRef.underlying`

Fixes #15799
---
 .../quoted/runtime/impl/QuotesImpl.scala      |  1 +
 library/src/scala/quoted/Quotes.scala         |  3 +++
 .../stdlibExperimentalDefinitions.scala       |  3 ++-
 tests/run-macros/i15799.check                 |  7 +++++++
 tests/run-macros/i15799/Macro_1.scala         | 14 +++++++++++++
 tests/run-macros/i15799/Test_2.scala          | 21 +++++++++++++++++++
 6 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 tests/run-macros/i15799.check
 create mode 100644 tests/run-macros/i15799/Macro_1.scala
 create mode 100644 tests/run-macros/i15799/Test_2.scala

diff --git a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
index a575238f7cd4..f32467bf3088 100644
--- a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
+++ b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
@@ -1844,6 +1844,7 @@ 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
 
diff --git a/library/src/scala/quoted/Quotes.scala b/library/src/scala/quoted/Quotes.scala
index 7668617fa71c..0d719741799b 100644
--- a/library/src/scala/quoted/Quotes.scala
+++ b/library/src/scala/quoted/Quotes.scala
@@ -2775,6 +2775,9 @@ 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
 
diff --git a/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala b/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
index 2c49ca46349e..c1960b074384 100644
--- a/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
+++ b/tests/run-custom-args/tasty-inspector/stdlibExperimentalDefinitions.scala
@@ -66,8 +66,9 @@ val experimentalDefinitionInLibrary = Set(
   //// New feature: Macro annotations
   "scala.annotation.MacroAnnotation",
 
-   //// New APIs: Quotes
+  //// New APIs: Quotes
   // Should be stabilized in 3.4.0
+  "scala.quoted.Quotes.reflectModule.TypeRefMethods.underlying",
   "scala.quoted.Quotes.reflectModule.defnModule.FunctionClass",
   // Can be stabilized in 3.4.0 (unsure) or later
   "scala.quoted.Quotes.reflectModule.CompilationInfoModule.XmacroSettings",
diff --git a/tests/run-macros/i15799.check b/tests/run-macros/i15799.check
new file mode 100644
index 000000000000..68eaef8bd2b8
--- /dev/null
+++ b/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)
diff --git a/tests/run-macros/i15799/Macro_1.scala b/tests/run-macros/i15799/Macro_1.scala
new file mode 100644
index 000000000000..7a4eea30f4b1
--- /dev/null
+++ b/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))
+  }
+}
diff --git a/tests/run-macros/i15799/Test_2.scala b/tests/run-macros/i15799/Test_2.scala
new file mode 100644
index 000000000000..ec1d6ad0c444
--- /dev/null
+++ b/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)
+}