Remove Nothing restriction on unused parameters

Author: nicolasstucki

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -384,11 +384,8 @@ object Checking {
         sym.setFlag(Private) // break the overriding relationship by making sym Private
       }
     checkApplicable(UnusedType, !sym.is(UnusedType))
-    if (sym.is(Unused)) {
+    if (sym.is(Unused))
       checkApplicable(Unused, !sym.is(MutableOrLazy))
-      if (sym.info.widen.finalResultType.isBottomType)
-        fail("unused " + sym.showKind + " cannot have type Nothing")
-    }
   }
 
   /** Check the type signature of the symbol `M` defined by `tree` does not refer

tests/neg/unused-Nothing.scala

@@ -2,7 +2,7 @@ object Test {
 
   def main(args: Array[String]): Unit = {
 
-    unused def !!! : Null = ???
+    unused def !!! : Nothing = ???
 
     try {
       fun(!!!)
@@ -12,7 +12,7 @@ object Test {
     }
   }
 
-  def fun(unused bottom: Null): Unit = {
+  def fun(unused bottom: Nothing): Unit = {
     println("fun")
   }
 }