SI-6902 Check unreachability under @unchecked

Only exhaustiveness checking should be disabled if the
scrutinee of a match as annotated as `: @unchecked`.
This was the pre-2.10.x behaviour.

This also fixes a variation of the closed ticket,
SI-6011. The exhaustiveness check is needed to
safely fallback from emitting a table switch if
duplicate cases are detected.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/files/run/t6011c.scala b/test/files/run/t6011c.scala
new file mode 100644
index 0000000000..0647e3f81a
--- /dev/null
+++ b/test/files/run/t6011c.scala
@@ -0,0 +1,13 @@
+object Test extends App {
+  // A variation of SI-6011, which eluded the fix
+  // in 2.10.0.
+  //
+  // duplicate keys in SWITCH, can't pick arbitrarily one of them to evict, see SI-6011.
+  // at scala.reflect.internal.SymbolTable.abort(SymbolTable.scala:50)
+  // at scala.tools.nsc.Global.abort(Global.scala:249)
+  // at scala.tools.nsc.backend.jvm.GenASM$JPlainBuilder$jcode$.emitSWITCH(GenASM.scala:1850)
+  ((1: Byte): @unchecked @annotation.switch) match {
+    case 1 => 2
+    case 1 => 3 // crash
+  }
+}