Merge pull request #14058 from dotty-staging/fix-13997

Check variance of RHS of opaque type
scala · Dec 7, 2021 · fc7e8c3 · fc7e8c3
2 parents 80ec523 + 9d729c3
commit fc7e8c3
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diff --git a/compiler/src/dotty/tools/dotc/transform/PostTyper.scala b/compiler/src/dotty/tools/dotc/transform/PostTyper.scala
@@ -378,6 +378,8 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
           else (tree.rhs, sym.info) match
             case (rhs: LambdaTypeTree, bounds: TypeBounds) =>
               VarianceChecker.checkLambda(rhs, bounds)
+              if sym.isOpaqueAlias then
+                VarianceChecker.checkLambda(rhs, TypeBounds.upper(sym.opaqueAlias))
             case _ =>
           processMemberDef(super.transform(tree))
         case tree: New if isCheckable(tree) =>

diff --git a/tests/neg/i13997.scala b/tests/neg/i13997.scala
@@ -0,0 +1,10 @@
+  opaque type CovariantArray[+A] = Array[A] // error
+
+  object CovariantArray:
+    def crash() =
+      val stringArray: CovariantArray[String] = Array("foo", "bar")
+      val anyArray: CovariantArray[Any] = stringArray
+      anyArray(0) = 42
+      stringArray(0).length
+
+  @main def Test = CovariantArray.crash()