Fix 1375: Infinite loop in interpreter

Author: kcsongor

src/dotty/tools/dotc/printing/SyntaxHighlighting.scala

@@ -4,6 +4,7 @@ package printing
 
 import parsing.Tokens._
 import scala.annotation.switch
+import scala.collection.mutable
 import scala.collection.mutable.StringBuilder
 
 /** This object provides functions for syntax highlighting in the REPL */
@@ -38,7 +39,7 @@ object SyntaxHighlighting {
   def apply(chars: Iterable[Char]): Vector[Char] = {
     var prev: Char = 0
     var remaining  = chars.toStream
-    val newBuf     = new StringBuilder
+    val newBuf     = new mutable.StringBuilder
 
     @inline def keywordStart =
       prev == 0 || prev == ' ' || prev == '{' || prev == '(' || prev == '\n'
@@ -77,10 +78,15 @@ object SyntaxHighlighting {
         (n: @switch) match {
           case '/'  =>
             if (remaining.nonEmpty) {
-              takeChar() match {
-                case '/' => eolComment()
-                case '*' => blockComment()
-                case x => newBuf += '/'; remaining = x #:: remaining
+              remaining.head match {
+                case '/' =>
+                  takeChar()
+                  eolComment()
+                case '*' =>
+                  takeChar()
+                  blockComment()
+                case x =>
+                  newBuf += '/'
               }
             } else newBuf += '/'
           case '='  =>
@@ -262,4 +268,5 @@ object SyntaxHighlighting {
 
     newBuf.toVector
   }
+
 }