Where do empty compilation units belong?

[Alex Buckley]

On 11/20/2018 10:54 AM, Alex Buckley wrote:
> From the above, it's hard to understand for which file an error is
> reported by Eclipse. In any case, as Jon indicated, if the file D.java
> is empty, then there is no stream of tokens matching the JLS 7.3
> production `CompilationUnit` and thus there is no compilation unit to
> discuss.

Jon points out that `OrdinaryCompilationUnit` will match an empty stream 
of tokens (I dislike the syntax-driven optionality here, but it's 
longstanding) so the file D.java could be regarded as a compilation unit 
with no package declaration, no import declarations, and no type 
declarations.

Per JLS 7.4.2, such a compilation unit is in an unnamed package, and 
must be associated with an unnamed module. (The "must" somewhat 
conflicts with the "may" in 
https://docs.oracle.com/javase/specs/jls/se11/html/jls-7.html#jls-7.3-310)

I would prefer 7.4.2 to say only that a compilation unit with no package 
declarations _and at least one type declaration_ is in an unnamed 
package (and must be associated with an unnamed module; 7.3 should 
enumerate that possibility). A compilation unit with no package 
declarations _and no type declarations_ would be deemed unobservable by 
7.3, and all these questions about what to do with empty files would 
disappear.

What do compiler engineers think?

Alex