Package, import and type declarations are allowed now in module-info.java by spec

[Alex Buckley]

The JLS doesn't prevent javac from rejecting a package declaration or an 
import declaration in a file called module-info.java.

In fact, since a package declaration or import declaration must be 
followed by a type declaration, and since a type declaration cannot use 
a hyphen, javac is free to take the optional rule from JLS 7.6 -- 
filename must align with type declaration -- and develop it further: 
rejecting a package declaration or import declaration in 
module-info.java because the filename cannot possibly align with any 
type declaration.

I can't speak to what a particular EA build of javac is doing with a 
particular option. javac options are irrelevant to the JLS. If a 
compiler accepts the Java language circa SE 9, then a module declaration 
is a valid compilation unit. What's the name of the file containing such 
a compilation unit? Anything the compiler likes.

Alex

On 3/9/2016 5:14 AM, Georgiy Rakov wrote:
> Hi Alex,
>
> if I understand correctly you mean about following assertions from JLS 7.6:
>
>     If and only if packages are stored in a file system (§7.2
>     <http://docs.oracle.com/javase/specs/jls/se8/html/jls-7.html#jls-7.2>),
>     the host system may choose to enforce the restriction that it is a
>     compile-time error if a type is not found in a file under a name
>     composed of the type name plus an extension (such as |.java|or
>     |.jav|) if either of the following is true:
>
>       *
>
>         The type is referred to by code in other compilation units of
>         the package in which the type is declared.
>
>       *
>
>         The type is declared |public|(and therefore is potentially
>         accessible from code in other packages).
>
> Literally these assertion doesn't make presented behavior corresponding
> to spec because the declared type is neither public nor being referred
> to from other sources being compiled.
>
> Nevertheless following sources doesn't compile either despite the fact
> that no types are declared there at all.
> Namely when only package is specified:
>
>     mod\module-info.java:
>     module mod {
>          exports pkg;
>     }
>
>     mod\pkg\module-info.java:
>     package pkg;
>
> then compiling it by following command line with javac from [2]:
>
>     javac -modulesourcepath . mod\module-info.java mod\pkg\module-info.java
>
> causes following output:
>
>     mod\pkg\module-info.java:1: error: expected 'module
>     package pkg;
>     ^
>     1 error
>
> When only import statment is specified:
>
>     mod\module-info.java:
>     module mod {
>          exports pkg;
>     }
>
>     mod\pkg\module-info.java:
>     import java.util.List;
>
> then compiling it by following command line with javac from [2]:
>
>     javac -modulesourcepath . mod\module-info.java mod\pkg\module-info.java
>
> causes following output:
>
>     mod\pkg\module-info.java:1: error: expected 'module'
>     import java.util.List;
>     ^
>     1 error
>
> Please see minimized test cases attached in tests23.zip. In order to
> reproduce, please:
>
> 1. Unzip the attached archive to some dir on Windows machined, say
> directory A;
> 2. Rename A\test2\test_bat to A\test2\test.bat and A\test3\test_bat to
> A\test3\test.bat;
> 3. Modify these two test.bat files by changing JDK_HOME variable to
> point to your jigsaw JDK 9 installation directory;
> 4. Run test.bat files in turn.
>
> BTW: javac behavior [2] currently differs depending on whether sources
> are compiled "in module" mode or not. By "module mode" I mean specifying
> modulesourcepath option. For instance without modulesourcepath option
> module declarations are not recognized as valid grammar while import
> declarations contained within module-info.java compile successfully.
> This can be seen by experimenting with test3 from the attached
> testcases. Now javac from [2] even can throw exception in "non-module"
> mode, please see https://bugs.openjdk.java.net/browse/JDK-8150733.
>
> Could you please tell if spec will specify somehow two modes of
> processing java-sources, now it [1] doesn't.
>
> [1] http://cr.openjdk.java.net/~mr/jigsaw/spec/lang-vm.html
> [2]
> http://download.java.net/java/jigsaw/archive/106/binaries/jigsaw-jdk-9-ea+106_windows-x86_bin.zip
>
> Thanks,
> Georgiy.
>
> On 26.02.2016 21:26, Alex Buckley wrote:
>> On 2/26/2016 8:37 AM, Georgiy Rakov wrote:
>>> current spec [1] now contains following assertions related to grammar:
>>>
>>>     A compilation unit (JLS 7.3) may contain a module declaration, in
>>>     which case the filename of the compilation unit is typically
>>>     |module-info.java|.
>>>
>>>     CompilationUnit:
>>>        [PackageDeclaration] {ImportDeclaration} {TypeDeclaration}
>>>        ModuleDeclaration
>>>
>>> These assertions allows to specify any of import, package or type
>>> declarations in any compilation unit, for instance module-info.java is
>>> allowed to contain any of the mentioned declarations. However currently
>>> javac in the latest jigsaw build [2] reports an error on such cases
>>> provided they are compiled in module mode. For example if we have
>>> following directory structure:
>>>
>>>     mod\module-info.java:
>>>     module mod {
>>>          exports pkg;
>>>     }
>>>
>>>     mod\pkg\module-info.java:
>>>     package pkg;
>>>
>>>     class C {
>>>     }
>>>
>>> then compiling it by following command line with javac from [2]:
>>>
>>>     javac -modulesourcepath . mod\module-info.java
>>> mod\pkg\module-info.java
>>>
>>> causes following output:
>>>
>>>     mod\pkg\module-info.java:1: error: expected 'module'
>>>     package pkg;
>>>     ^
>>>     1 error
>>
>> javac is merely choosing to implement the rule at the end of JLS 7.6
>> that a type declaration (optionally preceded by package/import
>> declarations) must be provided in a suitably named file.
>>
>> Perhaps I should say "a variant of the rule" because 7.6 as written
>> concerns a public type and your example has a package-access type.
>> Still, bottom line, javac is free to require that a compilation unit
>> which starts with a package declaration _must not_ be in a file called
>> foo-bar.java -- the hyphen indicates a name that can't possibly align
>> with the type declared in the compilation unit.
>>
>> The error message for mod\pkg\module-info.java could be a bit more
>> helpful, but that's a quality-of-implementation detail.
>>
>> Conversely, a compilation unit that contains a module declaration
>> _may_ be in a file called module-info.java, or in a file called
>> foo-bar.java, or in a file called mod_decl.JAV. The "typically" in [1]
>> is meant to indicate that the sub-clause on filename is non-normative.
>> This is akin to how a compilation unit that contains a package-access
>> type declaration for class C _may_ be in a file D.java.
>>
>> Alex
>