Generalize Scala 2 xyz$accessor$idx fix

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

@@ -454,13 +454,18 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
       // skip this member
       return NoSymbol
 
-    // Remove case accessor `next$access$1` and make `next` the case accessor
-    // TODO generalize to all Scala 2 accessors with this form
-    if owner == defn.ConsClass then
-      if name == nme.next then
-        flags = flags | CaseAccessor
-      else if name == "next$access$1".toTermName then
-        return NoSymbol
+    // Skip case accessor `<xyz>$access$<idx>` and make `<xyz>` the case accessor
+    if flags.is(CaseAccessor) && name.toString().contains("$access$") then
+      // The only way to know if the accessor needs the additional `CaseAccessor` flag is
+      // when we see the `<xyz>$access$<idx>` accessor. When we load `<xyz>` we have not
+      // loaded or have skipped `<xyz>$access$<idx>`. Furthermore, its flags are
+      // undistinguishable from non-case parameter accessors (example
+      // `case class Foo(private[p] var x: T)(private[p] var y: T)`).
+      val accessorIndex = name.toString().split('$').last.toInt
+      val accessors = owner.asClass.info.decls
+        .filter(decl => decl.isAllOf(Accessor | ParamAccessor) && !decl.name.endsWith("_="))
+      accessors(accessorIndex).setFlag(CaseAccessor)
+      return NoSymbol // skip `<xyz>$access$<idx>`
 
     name = name.adjustIfModuleClass(flags)
     if (flags.is(Method))

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 +1,8 @@
+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)")