From b1ce4f4127a35af9facb592999eec9e49b70f1cf Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 18 Mar 2019 09:49:40 +0100
Subject: [PATCH] Fix #6061: Handle malformed opaque type aliases

---
 compiler/src/dotty/tools/dotc/typer/Namer.scala | 4 +++-
 tests/neg/i6061.scala                           | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i6061.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index f1ba950f1cd2..0d5a5aa2e341 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -1039,7 +1039,7 @@ class Namer { typer: Typer =>
       val finalSelfInfo: TypeOrSymbol =
         if (cls.isOpaqueCompanion) {
           // The self type of an opaque companion is refined with the type-alias of the original opaque type
-          def refineOpaqueCompanionSelfType(mt: Type, stats: List[Tree]): RefinedType = (stats: @unchecked) match {
+          def refineOpaqueCompanionSelfType(mt: Type, stats: List[Tree]): Type = (stats: @unchecked) match {
             case (td @ TypeDef(localName, rhs)) :: _
             if td.mods.is(SyntheticOpaque) && localName == name.stripModuleClassSuffix =>
               // create a context owned by the current opaque helper symbol,
@@ -1053,6 +1053,8 @@ class Namer { typer: Typer =>
               RefinedType(mt, localName, bounds)
             case _ :: stats1 =>
               refineOpaqueCompanionSelfType(mt, stats1)
+            case _ =>
+              mt // can happen for malformed inputs.
           }
           selfInfo match {
             case self: Type =>
diff --git a/tests/neg/i6061.scala b/tests/neg/i6061.scala
new file mode 100644
index 000000000000..b1028d2889b3
--- /dev/null
+++ b/tests/neg/i6061.scala
@@ -0,0 +1,2 @@
+opaque object
+  // error
\ No newline at end of file