New highlighter based on tokens and untyped trees

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

@@ -596,6 +596,12 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
     }
   }
 
+  abstract class UntypedTreeTraverser extends UntypedTreeAccumulator[Unit] {
+    def traverse(tree: Tree)(implicit ctx: Context): Unit
+    def apply(x: Unit, tree: Tree)(implicit ctx: Context) = traverse(tree)
+    protected def traverseChildren(tree: Tree)(implicit ctx: Context) = foldOver((), tree)
+  }
+
   /** Fold `f` over all tree nodes, in depth-first, prefix order */
   class UntypedDeepFolder[X](f: (X, Tree) => X) extends UntypedTreeAccumulator[X] {
     def apply(x: X, tree: Tree)(implicit ctx: Context): X = foldOver(f(x, tree), tree)

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1493,7 +1493,9 @@ object Parsers {
         }
       }
       if (in.token == LPAREN && (!inClassConstrAnnots || isLegalAnnotArg))
-        parArgumentExprss(Apply(fn, parArgumentExprs()))
+        parArgumentExprss(
+          atPos(startOffset(fn)) { Apply(fn, parArgumentExprs()) }
+        )
       else fn
     }
 

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -83,8 +83,8 @@ object Formatting {
           hl.show
         case hb: HighlightBuffer =>
           hb.toString
-        case str: String if ctx.settings.color.value != "never" =>
-          new String(SyntaxHighlighting(str).toArray)
+        case str: String =>
+          SyntaxHighlighting.highlight(str)
         case _ => super.showArg(arg)
       }
   }