Where do empty compilation units belong?

Wed Nov 21 05:14:48 UTC 2018

"jigsaw-dev" <jigsaw-dev-bounces at openjdk.java.net> wrote on 21/11/2018 01:56:42 AM:

> From: Alex Buckley <alex.buckley at oracle.com
>
> 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.

Sorry for not being clear. C.java is fine and it's D.java that is being
reported by the Eclipse compiler.

> 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://urldefense.proofpoint.com/v2/url?
> u=https-3A__docs.oracle.com_javase_specs_jls_se11_html_jls-2D7.html-23jls-2D7.
> 3-2D310&d=DwIC-g&c=jf_iaSHvJObTbx-
> siA1ZOg&r=LuMqcl3PU0i2olgTvkVvFthzqyc_3wGfGooplpAvFsc&m=0-yB-
> s6iIk8sBeNaaAkAlma7IqqfciaUiZ0EyShDTLk&s=aRQM4fwhr3kUvHE9tcUkUscWSmnPllgXg08OI8VA80c&e=
> )
>
> 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.

That would be perfect and make things unambiguous. But for now, the paragraph above
is good enough for me.

> What do compiler engineers think?
>
> Alex
>