Working towards arc codegen (#13153)

fixes #13029

tests/destructor/tarc3.nim

@@ -0,0 +1,57 @@
+
+discard """
+  cmd: '''nim c --gc:arc $file'''
+"""
+
+when defined(cpp):
+  {.passC: "-std=gnu++17".}
+
+type
+  TokenKind* = enum
+    tkColon
+    tkComma
+    tkString
+    tkNumber
+    tkInt64
+    tkIdent
+
+  Token* = object
+    case kind*: TokenKind
+    of tkString: strVal*: string
+    of tkNumber: numVal*: float
+    of tkInt64: int64Val*: int64
+    of tkIdent: ident*: string
+    else: discard
+    pos*: Natural
+
+  BaseLexer* = object of RootObj
+    input*: string
+    pos*: Natural
+
+  Json5Lexer* = object of BaseLexer
+
+  JsonLexer* = object of BaseLexer
+    allowComments*: bool
+    allowSpecialFloats*: bool
+
+  Lexer* = Json5Lexer | JsonLexer
+
+  Parser[T: Lexer] = object
+    l: T
+    tok: Token
+    allowTrailingComma: bool
+    allowIdentifierObjectKey: bool
+
+proc initJson5Lexer*(input: string): Json5Lexer =
+  result.input = input
+
+proc parseJson5*(input: string)  =
+  var p = Parser[Json5Lexer](
+    l: initJson5Lexer(input),
+    allowTrailingComma: true,
+    allowIdentifierObjectKey: true
+  )
+
+
+let x = "string"
+parseJson5(x)