The current proposal doesn't exclude this possibility in the future, does it. Maybe one day you will be able to declare a class
public class! MyClass {
package! com.initech.accounting;Otherwise, I agree that the indication should be in the source, at least during the transitional years. In practice, looking for the presence or absence for T? vs. T! will be a good heuristic for whether the code assumes the new or the old semantics. The compiler could also warn or even error out when the code is obviously being compiled with the wrong semantics, that is, if ? or ! are present but all redundant.
Regarding the class syntax, you can have multiple (package-private) classes in the same file, so I wouldn’t do that. A simple solution would be to have an optional ! or ? at the very start of the source file (ignoring comments and whitespace), which means a regex could handle it (useful for external tooling), and it would also work in the absence of a package declaration (i.e. in the default package). Another reason to not put it on the package declaration is that it isn’t meant to apply to the whole package.
null-marked module accounting {
}