SI-9178 Don't eta expand param-less method types to SAMs

Otherwise, we can end up with a subtle source incompatibility with
the pre-SAM regime. Arguably we should phase out eta expansion to
Function0 as well, but I'll leave that for another day.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/run/t9178a.scala b/test/files/run/t9178a.scala
new file mode 100644
index 0000000000..4788841f8d
--- /dev/null
+++ b/test/files/run/t9178a.scala
@@ -0,0 +1,15 @@
+trait Sam { def apply(): Unit }
+abstract class Test {
+  def foo(): Sam
+  // no parens, instantiateToMethodType would wrap in a `new Sam { def apply = foo }`
+  // rather than applying to an empty param list() */
+  val f: Sam = foo
+}
+
+object Test extends Test {
+  lazy val samIAm = new Sam { def apply() {} }
+  def foo() = samIAm
+  def main(args: Array[String]): Unit = {
+    assert(f eq samIAm, f)
+  }
+}