SI-9223 By-name constructor params should not be aliased

Usually, the compiler tries avoids creating a field in a subclass
for a constructor parameter that is known to be stored in a field
in one of its superclasses.

However, in the enclosed test `run/t9223.scala`, this mechanism
confuses `=> A` with `A`, which results in a runtime
`ClassCastException`.

This commit avoids using param aliases for by-name parameters.

I have also added a test for something close the opposite case, where
the subclass has a strict parameter and the superclass has a by-name
parameter. This was working correctly before this patch.

2 files changed, 16 insertions, 0 deletions

diff --git a/test/files/run/t9223.scala b/test/files/run/t9223.scala
new file mode 100644
index 0000000000..78767b158d
--- /dev/null
+++ b/test/files/run/t9223.scala
@@ -0,0 +1,8 @@
+class X(val x: String)
+class Y(y: => String) extends X(y) { def f = y }
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    assert(new Y("hi").f == "hi")
+  }
+}
diff --git a/test/files/run/t9223b.scala b/test/files/run/t9223b.scala
new file mode 100644
index 0000000000..2afc7ddfe0
--- /dev/null
+++ b/test/files/run/t9223b.scala
@@ -0,0 +1,8 @@
+class X(x: => String) { def xx = x }
+class Y(y: String) extends X(y) { def f = y }
+
+object Test {
+  def main(args: Array[String]): Unit = {
+     assert(new Y("hi").f == "hi")
+  }
+}