Move withSpans out of desugarIdentPrefix

Author: nicolasstucki

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

@@ -1253,15 +1253,15 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def desugarIdent(tree: Ident)(implicit ctx: Context): Tree = {
     val qual = desugarIdentPrefix(tree)
     if (qual.isEmpty) tree
-    else qual.select(tree.symbol).withSpan(tree.span)
+    else qual.select(tree.symbol)
   }
 
   /** Recover identifier prefix (e.g. this) if it exists */
   def desugarIdentPrefix(tree: Ident)(implicit ctx: Context): Tree = tree.tpe match {
     case TermRef(prefix: TermRef, _) =>
-      ref(prefix).withSpan(tree.span)
+      ref(prefix)
     case TermRef(prefix: ThisType, _) =>
-      This(prefix.cls).withSpan(tree.span)
+      This(prefix.cls)
     case _ =>
       EmptyTree
   }

compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala

@@ -312,7 +312,10 @@ object TypeTestsCasts {
     }
     val expr = tree.fun match {
       case Select(expr, _) => expr
-      case i: Ident => desugarIdentPrefix(i)
+      case i: Ident =>
+        val expr = desugarIdentPrefix(i)
+        if (expr.isEmpty) expr
+        else expr.withSpan(i.span)
       case _ => EmptyTree
     }
     interceptWith(expr)