Drop redundant span computation

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1015,14 +1015,11 @@ object desugar {
    *      def $anonfun(params) = body
    *      Closure($anonfun)
    */
-  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = null, isContextual: Boolean)(implicit ctx: Context): Block = {
-    val span = params.headOption.fold(body.span)(_.span.union(body.span))
+  def makeClosure(params: List[ValDef], body: Tree, tpt: Tree = null, isContextual: Boolean)(implicit ctx: Context): Block =
     Block(
       DefDef(nme.ANON_FUN, Nil, params :: Nil, if (tpt == null) TypeTree() else tpt, body)
-        .withSpan(span)
         .withMods(synthetic | Artifact),
-      Closure(Nil, Ident(nme.ANON_FUN), if (isContextual) ContextualEmptyTree else EmptyTree)).withSpan(span)
-  }
+      Closure(Nil, Ident(nme.ANON_FUN), if (isContextual) ContextualEmptyTree else EmptyTree))
 
   /** If `nparams` == 1, expand partial function
    *