Fixed type adaptation problem in checkBounds

We need to adapt type parameter bounds with an as-ssen-from to the
prefix of the type constructor.

Makes pos/boundspropagation pass.

1 files changed, 18 insertions, 0 deletions

diff --git a/tests/pos/boundspropagation.scala b/tests/pos/boundspropagation.scala
new file mode 100644
index 000000000..164f1ae1a
--- /dev/null
+++ b/tests/pos/boundspropagation.scala
@@ -0,0 +1,18 @@
+// test contributed by @retronym
+object test1 {
+  class Base {
+    type N
+
+    class Tree[-T >: N]
+
+    def f(x: Any): Tree[N] = x match {
+      case y: Tree[_] => y
+    }
+  }
+  class Derived extends Base {
+    def g(x: Any): Tree[N] = x match {
+      case y: Tree[_] => y // now succeeds in dotc
+    }
+  }
+}
+