Add syntax highlighting support for string interpolator

Author: allanrenucci

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

@@ -59,12 +59,19 @@ object SyntaxHighlighting {
 
         // Branch order is important. For example,
         // `true` is at the same time a keyword and a literal
-        if (literalTokens.contains(token))
-          highlightRange(start, end, LiteralColor)
-        else if (alphaKeywords.contains(token))
-          highlightRange(start, end, KeywordColor)
-        else if (token == IDENTIFIER && name == nme.???)
-          highlightRange(start, end, Console.RED_B)
+        token match {
+          case _ if literalTokens.contains(token) =>
+            highlightRange(start, end, LiteralColor)
+          case STRINGPART =>
+            // String interpolation parts include `$` but
+            // we don't highlight it, hence the `-1`
+            highlightRange(start, end - 1, LiteralColor)
+          case _ if alphaKeywords.contains(token) =>
+            highlightRange(start, end, KeywordColor)
+          case IDENTIFIER if name == nme.??? =>
+            highlightRange(start, end, Console.RED_B)
+          case _ =>
+        }
       }
 
       object TreeHighlighter extends untpd.UntypedTreeTraverser {

compiler/test/dotty/tools/dotc/printing/SyntaxHighlightingTests.scala

@@ -62,11 +62,10 @@ class SyntaxHighlightingTests extends DottyTest {
     test("\"Hello\"", "<L|\"Hello\">")
     test("\"\"\"Hello\"\"\"", "<L|\"\"\"Hello\"\"\">")
 
-    // FIXME: '$' should not be colored (literal position is off by one)
-    // test("s\"Hello\"", "s<L|\"Hello\">")
-    // test("s\"Hello $name\"", "s<L|\"Hello <V|$name<L|\">")
-    // test("raw\"Hello\"", "raw<L|\"Hello\">")
-    // test("raw\"\"\"Hello\"\"\"", "raw<L|\"\"\"Hello\"\"\">")
+    test("s\"Hello\"", "<L|s\"Hello\">")
+    test("s\"Hello $name\"", "<L|s\"Hello >$name<L|\">")
+    test("s\"Hello ${name}\"", "<L|s\"Hello >${name}<L|\">")
+    test("raw\"Hello\"", "<L|raw\"Hello\">")
   }
 
   @Test