On 11/20/2018 12:26 PM, Alex Buckley wrote:
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
I think that would be useful but not necessary, since we are dealing
with the way the host system finds/handles compilation units.
It is the case that javac accepts and effectively ignores empty files;
that is nothing new or specific to the module system or
module-source-path. javac doesn't go out of its way to ignore them; it's
more that there is nothing in an empty file that needs to be checked.
Yes, 7.4.2 says that an empty file is in an unnamed package in an
unnamed module, and yes you can say it is weird to allow them in a
hierarchy on the module source path, but it would be equally weird to
forbid empty files in subdirectories of directories on the source path
or module source path. javac does reject non-empty compilation units
without a package declaration that are associated with a named module.
Generally, in addition to the various suggestions in JLS 7 regarding
restrictions that may be enforced when packages are stored in a file
system, javac uses the following rules in being a "host system" (7.2)
* Types that are looked up implicitly on the source path or module
source path must be in an appropriately named directory.
* Module membership is determined by examining the search path for
each module on the module source path to determine which search path
contains a directory that indirectly contains any given file. If
there is only one source hierarchy for each module, that simplifies
to finding the module declaration in the enclosing directory on the
module source path.
-- Jon
