[wix-devs] wix4: Handling invalid ids

[Bob Arnson]

I opened https://github.com/wixtoolset/issues/issues/5464 when I was finding and fixing the wix4 unit tests (see https://github.com/wixtoolset/wix4/pull/224). What happens is that CompilerCore.GetAttributeIdentifier returns null if the id isn't valid and other Parse* methods use it before checking for a null Id (to generate one, usually). I'm thinking that CompilerCore.GetAttributeIdentifier should throw a warning itself and return a special InvalidIdentifier that's a legal object but distinguishable as invalid for reporting. Anyone have a different suggestion?