Don't set PureInterface when a default param is present

The default param will be desugared into a method with a body, so
setting PureInterface would be wrong. The enclosed test previously
failed with a pickling difference, because the unpickler correctly
decided to not set the PureInterface flag since it saw the default param
method.

This fixes the tasty_dotc_util which failed since the last commit
because FreshNameCreator was now incorrectly recognized as a PureInterface.

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/tasty/default-param-interface.scala b/tests/tasty/default-param-interface.scala
new file mode 100644
index 000000000..919f4b627
--- /dev/null
+++ b/tests/tasty/default-param-interface.scala
@@ -0,0 +1,3 @@
+trait Foo {
+  def newName(prefix: String = "foo"): String
+}