Merge pull request scala#10509 from SethTisue/nullary-nilary-crashy-crashy

Don't crash issuing spurious nilary-overrides-nullary warning

Author: som-snytt

src/compiler/scala/tools/nsc/typechecker/RefChecks.scala

@@ -461,7 +461,8 @@ abstract class RefChecks extends Transform {
               }
               else if (other.paramss.isEmpty && !member.paramss.isEmpty &&
                 !javaDetermined(member) && !member.overrides.exists(javaDetermined) &&
-                !member.hasAnnotation(BeanPropertyAttr) && !member.hasAnnotation(BooleanBeanPropertyAttr)
+                !member.hasAnnotation(BeanPropertyAttr) && !member.hasAnnotation(BooleanBeanPropertyAttr) &&
+                member.pos.isDefined  // scala/bug#12851
               ) {
                 val msg = "method with a single empty parameter list overrides method without any parameter list"
                 val namePos = member.pos.focus.withEnd(member.pos.point + member.decodedName.length)

test/files/pos/t12851/C_2.scala

@@ -0,0 +1,2 @@
+// scalac: -Werror
+class C extends T2

test/files/pos/t12851/T_1.scala

@@ -0,0 +1,7 @@
+
+trait T1 {
+  def f: Int
+}
+trait T2 extends T1 {
+  def f() = 42
+}