From b59b901a8ab74635c43d9ef3bb1d9a3cce392c83 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Fri, 22 Sep 2023 13:55:24 +0200
Subject: [PATCH] Add reflect TypeRepr.dealiasKeepOpaques

From https://github.com/lampepfl/dotty/discussions/18562
---
 .../quoted/runtime/impl/QuotesImpl.scala      |  1 +
 library/src/scala/quoted/Quotes.scala         |  3 ++
 project/MiMaFilters.scala                     |  1 +
 .../run-macros/tasty-dealiasKeepOpaques.check | 10 +++++++
 .../tasty-dealiasKeepOpaques/Macro_1.scala    |  8 +++++
 .../tasty-dealiasKeepOpaques/Test_2.scala     | 29 +++++++++++++++++++
 6 files changed, 52 insertions(+)
 create mode 100644 tests/run-macros/tasty-dealiasKeepOpaques.check
 create mode 100644 tests/run-macros/tasty-dealiasKeepOpaques/Macro_1.scala
 create mode 100644 tests/run-macros/tasty-dealiasKeepOpaques/Test_2.scala

diff --git a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
index e27140459a49..908e5643fc71 100644
--- a/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
+++ b/compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala
@@ -1790,6 +1790,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
         def widenTermRefByName: TypeRepr = self.widenTermRefExpr
         def widenByName: TypeRepr = self.widenExpr
         def dealias: TypeRepr = self.dealias
+        def dealiasKeepOpaques: TypeRepr = self.dealiasKeepOpaques
         def simplified: TypeRepr = self.simplified
         def classSymbol: Option[Symbol] =
           if self.classSymbol.exists then Some(self.classSymbol.asClass)
diff --git a/library/src/scala/quoted/Quotes.scala b/library/src/scala/quoted/Quotes.scala
index 3d5896e74f66..174f1913220a 100644
--- a/library/src/scala/quoted/Quotes.scala
+++ b/library/src/scala/quoted/Quotes.scala
@@ -2652,6 +2652,9 @@ trait Quotes { self: runtime.QuoteUnpickler & runtime.QuoteMatching =>
         /** Follow aliases, annotated types until type is no longer alias type, annotated type. */
         def dealias: TypeRepr
 
+        /** Follow non-opaque aliases, annotated types until type is no longer alias type, annotated type. */
+        def dealiasKeepOpaques: TypeRepr
+
         /** A simplified version of this type which is equivalent wrt =:= to this type.
         *  Reduces typerefs, applied match types, and and or types.
         */
diff --git a/project/MiMaFilters.scala b/project/MiMaFilters.scala
index 954b18a5841b..ab8cf0785aa6 100644
--- a/project/MiMaFilters.scala
+++ b/project/MiMaFilters.scala
@@ -9,6 +9,7 @@ object MiMaFilters {
     ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule.ValOrDefDefMethods"),
     ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#defnModule.FunctionClass"),
     ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#defnModule.PolyFunctionClass"),
+    ProblemFilters.exclude[ReversedMissingMethodProblem]("scala.quoted.Quotes#reflectModule#TypeReprMethods.dealiasKeepOpaques"),
   )
   val TastyCore: Seq[ProblemFilter] = Seq(
     ProblemFilters.exclude[DirectMissingMethodProblem]("dotty.tools.tasty.TastyFormat.EXPLICITtpt"),
diff --git a/tests/run-macros/tasty-dealiasKeepOpaques.check b/tests/run-macros/tasty-dealiasKeepOpaques.check
new file mode 100644
index 000000000000..11835b6febbd
--- /dev/null
+++ b/tests/run-macros/tasty-dealiasKeepOpaques.check
@@ -0,0 +1,10 @@
+java.lang.String
+java.lang.String
+scala.collection.immutable.List[Test_2$package.A]
+scala.collection.immutable.List[scala.Int]
+Test_2$package.OA
+Test_2$package.OB
+Test_2$package.OC[scala.Int]
+Test_2$package.OA
+Test_2$package.OB
+Test_2$package.OC[scala.Int]
diff --git a/tests/run-macros/tasty-dealiasKeepOpaques/Macro_1.scala b/tests/run-macros/tasty-dealiasKeepOpaques/Macro_1.scala
new file mode 100644
index 000000000000..d1c4a482235d
--- /dev/null
+++ b/tests/run-macros/tasty-dealiasKeepOpaques/Macro_1.scala
@@ -0,0 +1,8 @@
+import scala.quoted.*
+
+inline def dealiasKeepOpaques[T]: String = ${ impl[T] }
+
+def impl[T: Type](using Quotes) : Expr[String] = {
+  import quotes.reflect.*
+  Expr(TypeRepr.of[T].dealiasKeepOpaques.show)
+}
diff --git a/tests/run-macros/tasty-dealiasKeepOpaques/Test_2.scala b/tests/run-macros/tasty-dealiasKeepOpaques/Test_2.scala
new file mode 100644
index 000000000000..1612816ccbc5
--- /dev/null
+++ b/tests/run-macros/tasty-dealiasKeepOpaques/Test_2.scala
@@ -0,0 +1,29 @@
+type A = String
+type B = List[A]
+type C[X] = List[X]
+
+opaque type OA = String
+object OA:
+  def test = println(dealiasKeepOpaques[OA])
+
+opaque type OB = List[A]
+object OB:
+  def test = println(dealiasKeepOpaques[OB])
+
+opaque type OC[X] = List[X]
+object OC:
+  def test = println(dealiasKeepOpaques[OC[Int]])
+
+
+@main def Test: Unit = {
+  println(dealiasKeepOpaques[String])
+  println(dealiasKeepOpaques[A])
+  println(dealiasKeepOpaques[B])
+  println(dealiasKeepOpaques[C[Int]])
+  println(dealiasKeepOpaques[OA])
+  println(dealiasKeepOpaques[OB])
+  println(dealiasKeepOpaques[OC[Int]])
+  OA.test
+  OB.test
+  OC.test
+}