fix-#4405 REPL highlight for StringLiteral

Author: fabianpage

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

@@ -34,12 +34,6 @@ object SyntaxHighlighting {
     index <- IF to ERASED // All alpha keywords
   } yield tokenString(index)
 
-  private val interpolationPrefixes =
-    'A' :: 'B' :: 'C' :: 'D' :: 'E' :: 'F' :: 'G' :: 'H' :: 'I' :: 'J' :: 'K' ::
-    'L' :: 'M' :: 'N' :: 'O' :: 'P' :: 'Q' :: 'R' :: 'S' :: 'T' :: 'U' :: 'V' ::
-    'W' :: 'X' :: 'Y' :: 'Z' :: '$' :: '_' :: 'a' :: 'b' :: 'c' :: 'd' :: 'e' ::
-    'f' :: 'g' :: 'h' :: 'i' :: 'j' :: 'k' :: 'l' :: 'm' :: 'n' :: 'o' :: 'p' ::
-    'q' :: 'r' :: 's' :: 't' :: 'u' :: 'v' :: 'w' :: 'x' :: 'y' :: 'z' :: Nil
 
   private val typeEnders =
    '{'  :: '}' :: ')' :: '(' :: '[' :: ']' :: '=' :: ' ' :: ',' :: '.' :: '|' ::
@@ -66,16 +60,44 @@ object SyntaxHighlighting {
       taken
     }
 
+    def isUpper(c: Char) = c.isUpper || c == '_' || c == '$'
+
+    def opChar(c:Char) = (c: @switch) match {
+      case '~' | '!' | '@' | '#' | '%' |
+           '^' | '*' | '+' | '-' | '<' |
+           '>' | '?' | ':' | '=' | '&' |
+           '|' | '\\' | '/' => true
+      case _ => false
+    }
+
+    def tryInterpolatorPrefix(n: Char, remaining: Stream[Char]): Option[String] = {
+      if (isUpper(n) || n.isLower) {
+        val beforeUnderscore = remaining.takeWhile(c =>
+          c.isUpper || c.isLower || c.isDigit
+        )
+        val suffix = remaining.drop(beforeUnderscore.length) match {
+          case '_' +: afterUnderscore => '_' +: afterUnderscore.drop(1).takeWhile(opChar)
+          case _ => Seq.empty
+        }
+        Some(((n +: beforeUnderscore) ++ suffix).mkString)
+      } else {
+        None
+      }
+    }
+
+
     while (remaining.nonEmpty) {
       val n = takeChar()
-      if (interpolationPrefixes.contains(n)) {
-        // Interpolation prefixes are a superset of the keyword start chars
-        val next = remaining.take(3).mkString
-        if (next.startsWith("\"")) {
-          newBuf += n
-          prev = n
-          if (remaining.nonEmpty) takeChar() // drop 1 for appendLiteral
-          appendString('"', next == "\"\"\"")
+
+      val optInterpPrefix = tryInterpolatorPrefix(n, remaining)
+      if (optInterpPrefix.isDefined) {
+        val interpPrefix: String = optInterpPrefix.get
+        val after = remaining.drop(interpPrefix.length - 1).take(3).mkString
+        if (after.startsWith("\"")) {
+          newBuf ++= interpPrefix
+          prev = interpPrefix.last
+          if (remaining.nonEmpty) takeChars(interpPrefix.length)
+          appendString('"', after == "\"\"\"", inInterpolation = true)
         } else {
           if (n.isUpper && (keywordStart || prev == '.')) {
             appendWhile(n, !typeEnders.contains(_), typeDef)
@@ -116,7 +138,7 @@ object SyntaxHighlighting {
           case '@'  =>
             appendWhile('@', !typeEnders.contains(_), annotation)
           case '\"' =>
-            appendString('\"', multiline = remaining.take(2).mkString == "\"\"")
+            appendString('\"', multiline = remaining.take(2).mkString == "\"\"", false)
           case '\'' =>
             appendSingleQuote('\'')
           case '`'  =>
@@ -181,11 +203,10 @@ object SyntaxHighlighting {
       newBuf append NoColor
     }
 
-    def appendString(delim: Char, multiline: Boolean = false) = {
+    def appendString(delim: Char, multiline: Boolean = false, inInterpolation: Boolean) = {
       var curr: Char      = 0
       var continue        = true
       var closing         = 0
-      val inInterpolation = interpolationPrefixes.contains(prev)
       newBuf append (LiteralColor + delim)
 
       def shouldInterpolate =