Fix highlighting for symbolic symbol literals

.gitignore

@@ -1,3 +1,4 @@
 node_modules
 
 *.vsix
+.metals

src/typescript/Scala.tmLanguage.ts

@@ -6,6 +6,9 @@ const digit  = "[0-9]"
 const letterOrDigit = `${letter}|${digit}`
 const alphaId = `${letter}+`
 const simpleInterpolatedVariable  = `${letter}(?:${letterOrDigit})*` // see SIP-11 https://docs.scala-lang.org/sips/string-interpolation.html
+const opchar = `[!#%&*+\\-\\/:<>=?@^|~[\\p{Sm}\\p{So}]]`
+const idrest = `${letter}(?:${letterOrDigit})*(?:((?<=_))${opchar}+)?`
+const plainid = `(?:${idrest}|(?:${opchar})+)`
 
 export const scalaTmLanguage: TmLanguage = {
   fileTypes: [
@@ -601,7 +604,7 @@ export const scalaTmLanguage: TmLanguage = {
       }
     },
     'scala-symbol': {
-      match: "'\\w+(?=[^'\\w]|$)",
+      match: `(?>'${plainid})(?!')`,
       name: 'constant.other.symbol.scala'
     },
     'meta-brackets': {

tests/snap/lexical.test.scala.snap

@@ -378,10 +378,9 @@
 #           ^^ source.scala
 #             ^^^^^^ source.scala constant.other.symbol.scala
 #                   ^^ source.scala
-#                     ^ source.scala constant.character.literal.scala punctuation.definition.character.begin.scala
-#                      ^^^ source.scala constant.character.literal.scala invalid.illegal.character-literal-too-long
-#                         ^ source.scala constant.character.literal.scala punctuation.definition.character.end.scala
-#                          ^ source.scala keyword.operator.arithmetic.scala
+#                     ^^ source.scala constant.other.symbol.scala
+#                       ^^ source.scala
+#                         ^^ source.scala constant.other.symbol.scala
 #                           ^ source.scala
 #                            ^ source.scala meta.bracket.scala
 >}

tests/unit/symbol.test.scala

@@ -0,0 +1,37 @@
+// SYNTAX TEST "source.scala"
+
+object Unicode {
+
+    val blue = '* //red
+//            ^ source.scala
+//             ^^ source.scala constant.other.symbol.scala
+//               ^ source.scala
+    val stillRed = '*
+//                 ^^ source.scala constant.other.symbol.scala
+    val invalidSymbol  = '**_x //'
+//                       ^^^ source.scala constant.other.symbol.scala
+//                          ^^^ source.scala
+    val symbolFollowedByOp = 'symbol*
+//                           ^^^^^^^ source.scala constant.other.symbol.scala
+//                                  ^ source.scala keyword.operator.arithmetic.scala
+    val symbolEndedWithOp  = 'symbol_*
+//                           ^^^^^^^^^ source.scala constant.other.symbol.scala
+    val unclosedSymbol = '1 //'
+//                       ^ source.scala constant.character.literal.scala punctuation.definition.character.begin.scala
+//                        ^^^^ source.scala constant.character.literal.scala invalid.illegal.character-literal-too-long
+//                            ^ source.scala constant.character.literal.scala punctuation.definition.character.end.scala
+    val symbolWithDigit = 'symbol1 //'
+//                        ^^^^^^^^ source.scala constant.other.symbol.scala
+    val characterLit = 'x'
+//                     ^ source.scala constant.character.literal.scala punctuation.definition.character.begin.scala
+//                      ^ source.scala constant.character.literal.scala
+//                       ^ source.scala constant.character.literal.scala punctuation.definition.character.end.scala
+    val greekSymbol = 'ξφδ
+//                    ^^^^ source.scala constant.other.symbol.scala
+    val greekSymbolDigit = 'φδφ0
+//                         ^^^^^ source.scala constant.other.symbol.scala
+    val greekSymbolWithOp = 'δφξφξ_+-
+//                          ^^^^^^^^^ source.scala constant.other.symbol.scala
+    val multiOpSymbol = '***
+//                      ^^^^ constant.other.symbol.scala
+}