Symbol references may change on any source code changes. Having symbols in the model will make your source generator rerun on every key press. I mean here, which uses this as the model.
The best practice is to store the fully qualified names and then find them in the output generation step.
Because of the use of XML DOC comments, many CS1587 warnings are generated during compilation.
I think you should replace comments like "///" to the usual "//"
E.g. being able to specify the default options for null checks could be useful. I want to get rid of the autogenerated null checks in the constructor by default. I can't do that by default, being forced to pass in NullChecks = NullChecks.Never manually on each invocation.
I suggest adding a Default option to the enum, which would mean that it draws the value based on the ambient configuration, which could be configured via an assembly level attribute or an MSBuild property.