Reinterpret xyz$access$i when unpickling from Scala 2

Fixes scala#18884

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -462,6 +462,14 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
       flags &~= Method | Accessor
       if !flags.is(StableRealizable) then flags |= Mutable
 
+    // Skip case accessor `<xyz>$access$<idx>` and keep track of their name to make `<xyz>` the case accessor
+    if flags.is(CaseAccessor) && name.toString().contains("$access$") then
+      val accessorName = name.toString().split('$').head.toTermName // <xyz>
+      symScopes(owner) // we assume that the `<xyz>` is listed before the accessor and hence is already entered in the scope
+        .find(decl => decl.isAllOf(ParamAccessor) && decl.name == accessorName)
+        .setFlag(CaseAccessor)
+      return NoSymbol // skip this member
+
     name = name.adjustIfModuleClass(flags)
     if (flags.is(Method))
       name =

compiler/test/dotty/tools/backend/jvm/DottyBytecodeTests.scala

@@ -1058,7 +1058,7 @@ class DottyBytecodeTests extends DottyBytecodeTest {
         TypeOp(CHECKCAST, "scala/collection/immutable/$colon$colon"),
         VarOp(ASTORE, 3),
         VarOp(ALOAD, 3),
-        Invoke(INVOKEVIRTUAL, "scala/collection/immutable/$colon$colon", "next$access$1", "()Lscala/collection/immutable/List;", false),
+        Invoke(INVOKEVIRTUAL, "scala/collection/immutable/$colon$colon", "next", "()Lscala/collection/immutable/List;", false),
         VarOp(ASTORE, 4),
         VarOp(ALOAD, 3),
         Invoke(INVOKEVIRTUAL, "scala/collection/immutable/$colon$colon", "head", "()Ljava/lang/Object;", false),
@@ -1112,7 +1112,7 @@ class DottyBytecodeTests extends DottyBytecodeTest {
         Invoke(INVOKESTATIC, "scala/runtime/BoxesRunTime", "unboxToInt", "(Ljava/lang/Object;)I", false),
         VarOp(ISTORE, 4),
         VarOp(ALOAD, 3),
-        Invoke(INVOKEVIRTUAL, "scala/collection/immutable/$colon$colon", "next$access$1", "()Lscala/collection/immutable/List;", false),
+        Invoke(INVOKEVIRTUAL, "scala/collection/immutable/$colon$colon", "next", "()Lscala/collection/immutable/List;", false),
         VarOp(ASTORE, 5),
         Op(ICONST_1),
         VarOp(ILOAD, 4),

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -616,7 +616,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
       def scala2Command(): Array[String] = {
         assert(!flags.options.contains("-scalajs"),
-          "Compilation tests with Scala.js on Scala 2 are not supported.\nThis test can be blacklisted in compiler/test/dotc/*-scala-js.blacklist")
+          "Compilation tests with Scala.js on Scala 2 are not supported.\nThis test can be skipped using the `// scalajs: --skip` tag")
         val stdlibClasspath = artifactClasspath("org.scala-lang", "scala-library")
         val scalacClasspath = artifactClasspath("org.scala-lang", "scala-compiler")
         val flagsArgs = flags

tests/neg/i18884.scala

@@ -0,0 +1,2 @@
+def test(xs: ::[Int]): List[Int] =
+  xs.next$access$1 // error

tests/run/i18884.check

@@ -0,0 +1,4 @@
+Foo1(1)
+Foo2(2, 3)
+Foo3(4, 5)
+Foo4(6, 7)

tests/run/i18884/A_1_c2.13.12.scala

@@ -0,0 +1,10 @@
+// scalajs: --skip
+
+package lib
+
+case class Foo1(private[lib] var x: Int) {}
+case class Foo2(private[lib] var x: Int, private[lib] var y: Int)
+case class Foo3(private[lib] var x: Int, var y: Int)
+case class Foo4(var x: Int, private[lib] var y: Int) {
+  val z: Int = x
+}

tests/run/i18884/B_2.scala

@@ -0,0 +1,14 @@
+import lib.*
+
+@main def Test: Unit =
+  test(new Foo1(1))
+  test(new Foo2(2, 3))
+  test(new Foo3(4, 5))
+  test(new Foo4(6, 7))
+
+def test(any: Any): Unit =
+  any match
+    case Foo1(x) => println(s"Foo1($x)")
+    case Foo2(x, y) => println(s"Foo2($x, $y)")
+    case Foo3(x, y) => println(s"Foo3($x, $y)")
+    case Foo4(x, y) => println(s"Foo4($x, $y)")

tests/run/typeclass-derivation3.check

@@ -9,6 +9,6 @@ Cons(hd = Cons(hd = 11, tl = Cons(hd = 22, tl = Cons(hd = 33, tl = Nil))), tl =
 Cons(hd = Left(x = 1), tl = Cons(hd = Right(x = Pair(x = 2, y = 3)), tl = Nil))
 Cons(hd = Left(x = 1), tl = Cons(hd = Right(x = Pair(x = 2, y = 3)), tl = Nil))
 true
-::(head = 1, next$access$1 = ::(head = 2, next$access$1 = ::(head = 3, next$access$1 = Nil())))
-::(head = ::(head = 1, next$access$1 = Nil()), next$access$1 = ::(head = ::(head = 2, next$access$1 = ::(head = 3, next$access$1 = Nil())), next$access$1 = Nil()))
-::(head = Nil(), next$access$1 = ::(head = ::(head = 1, next$access$1 = Nil()), next$access$1 = ::(head = ::(head = 2, next$access$1 = ::(head = 3, next$access$1 = Nil())), next$access$1 = Nil())))
+::(head = 1, next = ::(head = 2, next = ::(head = 3, next = Nil())))
+::(head = ::(head = 1, next = Nil()), next = ::(head = ::(head = 2, next = ::(head = 3, next = Nil())), next = Nil()))
+::(head = Nil(), next = ::(head = ::(head = 1, next = Nil()), next = ::(head = ::(head = 2, next = ::(head = 3, next = Nil())), next = Nil())))