Merge pull request #3601 from dotty-staging/fix-paramInfoAsSeenFrom

Fix #3591: fix paramInfoAsSeenFrom for type lambdas

Author: smarter

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -3060,7 +3060,7 @@ object Types {
     def isTypeParam(implicit ctx: Context) = tl.paramNames.head.isTypeName
     def paramName(implicit ctx: Context) = tl.paramNames(n)
     def paramInfo(implicit ctx: Context) = tl.paramInfos(n)
-    def paramInfoAsSeenFrom(pre: Type)(implicit ctx: Context) = paramInfo
+    def paramInfoAsSeenFrom(pre: Type)(implicit ctx: Context) = paramInfo.asSeenFrom(pre, pre.classSymbol)
     def paramInfoOrCompleter(implicit ctx: Context): Type = paramInfo
     def paramVariance(implicit ctx: Context): Int = tl.paramNames(n).variance
     def paramRef(implicit ctx: Context): Type = tl.paramRefs(n)

tests/pos/i3591.scala

@@ -0,0 +1,9 @@
+class Foo {
+  class A
+
+  type Bla[X <: A] = X
+}
+
+class Bar extends Foo {
+  val y: Bla[A] = ???
+}