From f3f537b480626b76ffc29f5976c9da8ed9f84912 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 20 Apr 2020 10:24:17 +0200
Subject: [PATCH] Fix #8750: Strip opaque refinements when checking self type

Strip opaque refinements when checking that a class is instantiatable
---
 compiler/src/dotty/tools/dotc/typer/Checking.scala | 8 +++++++-
 tests/pos/i8750.scala                              | 4 ++++
 2 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i8750.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Checking.scala b/compiler/src/dotty/tools/dotc/typer/Checking.scala
index 89e4d6354713..77ab4829baa4 100644
--- a/compiler/src/dotty/tools/dotc/typer/Checking.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Checking.scala
@@ -175,10 +175,16 @@ object Checking {
         if (cls.isOneOf(AbstractOrTrait))
           ctx.error(CantInstantiateAbstractClassOrTrait(cls, isTrait = cls.is(Trait)), posd.sourcePos)
         if (!cls.is(Module)) {
+          def (tp: Type).stripOpaques: Type = tp match
+            case RefinedType(parent, name, _) if cls.info.decl(name).symbol.isOpaqueAlias =>
+              parent.stripOpaques
+            case _ =>
+              tp
           // Create a synthetic singleton type instance, and check whether
           // it conforms to the self type of the class as seen from that instance.
           val stp = SkolemType(tp)
-          val selfType = cls.asClass.givenSelfType.asSeenFrom(stp, cls)
+          val selfType =
+            cls.asClass.givenSelfType.stripOpaques.asSeenFrom(stp, cls)
           if (selfType.exists && !(stp <:< selfType))
             ctx.error(DoesNotConformToSelfTypeCantBeInstantiated(tp, selfType), posd.sourcePos)
         }
diff --git a/tests/pos/i8750.scala b/tests/pos/i8750.scala
new file mode 100644
index 000000000000..a88cfb51acd2
--- /dev/null
+++ b/tests/pos/i8750.scala
@@ -0,0 +1,4 @@
+class Abc:
+  opaque type Log = Double
+
+val v : Abc = new Abc
\ No newline at end of file