From ed1f2aff286094a09b7bcbe9e95e0439ccefe8d2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Fri, 6 Oct 2023 10:36:55 +0200
Subject: [PATCH] Fix #18658: Handle varargs of generic types in
 `JSExportsGen`.

When extracting the type of a varargs parameter, we have to go back
to before erasure. However, that gives us a non-erased type inside
as well. We need to re-erase that type to get something sensible
for the back-end.

[Cherry-picked 45388755873246a8f5294b91dc3ad67ee2a8adfe]
---
 .../tools/dotc/transform/sjs/JSSymUtils.scala |  2 +-
 .../jsinterop/NonNativeJSTypeTestScala3.scala | 78 +++++++++++++++++++
 2 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 tests/sjs-junit/test/org/scalajs/testsuite/jsinterop/NonNativeJSTypeTestScala3.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/sjs/JSSymUtils.scala b/compiler/src/dotty/tools/dotc/transform/sjs/JSSymUtils.scala
index 115d41dd3d46..ae6635bce622 100644
--- a/compiler/src/dotty/tools/dotc/transform/sjs/JSSymUtils.scala
+++ b/compiler/src/dotty/tools/dotc/transform/sjs/JSSymUtils.scala
@@ -185,7 +185,7 @@ object JSSymUtils {
         val list =
           for ((name, info) <- paramNamesAndTypes) yield {
             val v =
-              if (info.isRepeatedParam) Some(info.repeatedToSingle.widenDealias)
+              if (info.isRepeatedParam) Some(TypeErasure.erasure(info.repeatedToSingle))
               else None
             name -> v
           }
diff --git a/tests/sjs-junit/test/org/scalajs/testsuite/jsinterop/NonNativeJSTypeTestScala3.scala b/tests/sjs-junit/test/org/scalajs/testsuite/jsinterop/NonNativeJSTypeTestScala3.scala
new file mode 100644
index 000000000000..ceb29d39b6a0
--- /dev/null
+++ b/tests/sjs-junit/test/org/scalajs/testsuite/jsinterop/NonNativeJSTypeTestScala3.scala
@@ -0,0 +1,78 @@
+package org.scalajs.testsuite.jsinterop
+
+import org.junit.Assert.*
+import org.junit.Test
+
+import scala.scalajs.js
+import scala.scalajs.js.annotation.*
+
+class NonNativeJSTypeTestScala3 {
+  import NonNativeJSTypeTestScala3.*
+
+  @Test
+  def overloadWithVarargOfGenericType(): Unit = {
+    class OverloadWithVarargOfGenericType extends js.Object {
+      def overloaded(x: Int): Int = x
+      def overloaded(xs: (Int, Int)*): Int = xs.size
+    }
+
+    val obj = new OverloadWithVarargOfGenericType
+    assertEquals(5, obj.overloaded(5))
+    assertEquals(1, obj.overloaded((5, 6)))
+    assertEquals(2, obj.overloaded((1, 2), (3, 4)))
+  }
+
+  @Test
+  def overloadWithVarargOfValueClass(): Unit = {
+    class OverloadWithVarargOfValueClass extends js.Object {
+      def overloaded(x: Int): Int = x
+      def overloaded(xs: VC*): Int = xs.size
+    }
+
+    val obj = new OverloadWithVarargOfValueClass
+    assertEquals(5, obj.overloaded(5))
+    assertEquals(1, obj.overloaded(new VC(5)))
+    assertEquals(2, obj.overloaded(new VC(5), new VC(6)))
+  }
+
+  @Test
+  def overloadWithVarargOfGenericValueClass(): Unit = {
+    class OverloadWithVarargOfGenericValueClass extends js.Object {
+      def overloaded(x: Int): Int = x
+      def overloaded(xs: GenVC[Int]*): Int = xs.size
+    }
+
+    val obj = new OverloadWithVarargOfGenericValueClass
+    assertEquals(5, obj.overloaded(5))
+    assertEquals(1, obj.overloaded(new GenVC(5)))
+    assertEquals(2, obj.overloaded(new GenVC(5), new GenVC(6)))
+  }
+
+  @Test
+  def overloadWithVarargOfOpaqueTypeAlias(): Unit = {
+    import OpaqueContainer.*
+
+    class OverloadWithVarargOfOpaqueTypeAlias extends js.Object {
+      def overloaded(x: String): Int = x.toInt
+      def overloaded(xs: OpaqueInt*): Int = xs.size
+    }
+
+    val obj = new OverloadWithVarargOfOpaqueTypeAlias
+    assertEquals(5, obj.overloaded("5"))
+    assertEquals(1, obj.overloaded(fromInt(5)))
+    assertEquals(2, obj.overloaded(fromInt(5), fromInt(6)))
+  }
+}
+
+object NonNativeJSTypeTestScala3 {
+  final class VC(val x: Int) extends AnyVal
+
+  final class GenVC[T](val x: T) extends AnyVal
+
+  object OpaqueContainer {
+    opaque type OpaqueInt = Int
+
+    def fromInt(x: Int): OpaqueInt = x
+    def toInt(x: OpaqueInt): Int = x
+  }
+}