SI-4440 workaround: avoid outer accessor that'll vanish

outer accessors of final classes are dropped in constructors
apply some foresight in explicit outer and replace those doomed outer checks by `true`
(since this is unfortunate, we generate an unchecked warning)

3 files changed, 33 insertions, 0 deletions

diff --git a/test/files/neg/t4440.check b/test/files/neg/t4440.check
new file mode 100644
index 0000000000..2861dc3040
--- /dev/null
+++ b/test/files/neg/t4440.check
@@ -0,0 +1,13 @@
+t4440.scala:12: error: The outer reference in this type test cannot be checked at run time.
+    case _: b.Inner => println("b")
+          ^
+t4440.scala:13: error: The outer reference in this type test cannot be checked at run time.
+    case _: a.Inner => println("a") // this is the case we want
+          ^
+t4440.scala:16: error: The outer reference in this type test cannot be checked at run time.
+    case _: a.Inner => println("a")
+          ^
+t4440.scala:17: error: The outer reference in this type test cannot be checked at run time.
+    case _: b.Inner => println("b") // this is the case we want
+          ^
+four errors found
diff --git a/test/files/neg/t4440.flags b/test/files/neg/t4440.flags
new file mode 100644
index 0000000000..779916d58f
--- /dev/null
+++ b/test/files/neg/t4440.flags
@@ -0,0 +1 @@
+-unchecked -Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/neg/t4440.scala b/test/files/neg/t4440.scala
new file mode 100644
index 0000000000..383b141edd
--- /dev/null
+++ b/test/files/neg/t4440.scala
@@ -0,0 +1,19 @@
+// constructors used to drop outer fields when they were not accessed
+// however, how can you know (respecting separate compilation) that they're not accessed!?
+class Outer { final class Inner }
+
+// the matches below require Inner's outer pointer
+// until SI-4440 is fixed properly, we can't make this a run test
+// in principle, the output should be "a\nb", but without outer checks it's "b\na"
+object Test extends App {
+  val a = new Outer
+  val b = new Outer
+  (new a.Inner: Any) match {
+    case _: b.Inner => println("b")
+    case _: a.Inner => println("a") // this is the case we want
+  }
+  (new b.Inner: Any) match {
+    case _: a.Inner => println("a")
+    case _: b.Inner => println("b") // this is the case we want
+  }
+}