String interpolation breaks on quotes

[bradyt]

In the following, dart-mode does not match the string interpolation at all, and the (s) is not fontified being contained in the string.

class ArgumentError extends Error {
  String get _errorName => "Invalid argument${!_hasValue ? "(s)" : ""}";
}

[bradyt]

I'm not sure why we are highlighting string interpolations as variables, since the idiom in place is to highlight variables when they are declared. But even if we disable the highlighting as variable, we have the bigger issue that nested strings are not fontified as strings. Fixing that should be a higher priority. We might next consider highlighting string interpolation as if it was code, not in a string. Though, this might be a challenging recursion situation, with nested string interpolations.

[bradyt]

nix-mode seems to have some logic for recursive string interpolation that we could use. I think the essential idea is they are adding properties to the text to track interpolation state.