Allow private objects containing opaque types

Author: odersky

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -537,7 +537,7 @@ object Checking {
     checkCombination(Private, Protected)
     checkCombination(Abstract, Override)
     checkCombination(Private, Override)
-    checkCombination(Private, Opaque)
+    if sym.isType && !sym.isClass then checkCombination(Private, Opaque)
     checkCombination(Lazy, Inline)
     // The issue with `erased inline` is that the erased semantics get lost
     // as the code is inlined and the reference is removed before the erased usage check.

tests/neg/i14660.scala

@@ -1,2 +1,8 @@
 class Bar:
   private opaque type Baz = Int // error
+
+  private object Foo:
+    opaque type O = Int // OK
+
+  val x: Baz = 1
+