Improve interpolated raw string literal parsing

[tamasvajk]

The below sample produces a parsing error:

int x = 1;
var a = $$""""
    aaa
    {
    """
    {{x}}
    """
    }
    bbb
    """";
System.Console.WriteLine(a);

I think the only option is to handle this case in an external scanner. That could keep track of the number of $, " and { symbols.

[damieng]

I suspect we're also going to need an external scanner for XML doc literals.

[tamasvajk]

@amaanq I see that #333 will close this issue, but I don't think the issue is completely solved. I'm getting the below tree on the above code fragment:

❯ tree-sitter parse a.cs
(compilation_unit [0, 0] - [10, 28]
  (global_statement [0, 0] - [0, 10]
    (local_declaration_statement [0, 0] - [0, 10]
      (variable_declaration [0, 0] - [0, 9]
        type: (predefined_type [0, 0] - [0, 3])
        (variable_declarator [0, 4] - [0, 9]
          name: (identifier [0, 4] - [0, 5])
          (integer_literal [0, 8] - [0, 9])))))
  (global_statement [1, 0] - [4, 7]
    (local_declaration_statement [1, 0] - [4, 7]
      (variable_declaration [1, 0] - [4, 7]
        type: (implicit_type [1, 0] - [1, 3])
        (variable_declarator [1, 4] - [4, 7]
          name: (identifier [1, 4] - [1, 5])
          (interpolated_string_expression [1, 8] - [4, 7]
            (interpolation_dollar [1, 8] - [1, 10])
            (string_content [1, 13] - [3, 4])
            (string_content [3, 4] - [4, 4]))))))
  (ERROR [5, 4] - [9, 9]
    (initializer_expression [5, 4] - [5, 9]
      (initializer_expression [5, 5] - [5, 8]
        (identifier [5, 6] - [5, 7]))))
  (global_statement [10, 0] - [10, 28]
    (local_declaration_statement [10, 0] - [10, 28]
      (variable_declaration [10, 0] - [10, 27]
        type: (qualified_name [10, 0] - [10, 24]
          qualifier: (qualified_name [10, 0] - [10, 14]
            qualifier: (identifier [10, 0] - [10, 6])
            name: (identifier [10, 7] - [10, 14]))
          name: (identifier [10, 15] - [10, 24]))
        (variable_declarator [10, 24] - [10, 27]
          (tuple_pattern [10, 24] - [10, 27]
            name: (identifier [10, 25] - [10, 26])))))))
a.cs    0 ms    (MISSING ";" [4, 7] - [4, 7])

[amaanq]

updated, I hadn't even noticed the 4 quotes nor was it mentioned on the MS docs, but I found a different page that briefly mentioned it, thanks