JEP proposed to target JDK 11: 330: Launch Single-File Source-Code Programs

[Ben Evans]

What about special-casing javac to interpret #! as a single-line
comment marker (synonym for //), for the first line of an input file,
and nowhere else?

Thanks,

Ben

On Thu, May 17, 2018 at 9:50 PM, Roman Kennke <roman at kennke.org> wrote:
> Am 17.05.2018 um 22:12 schrieb mark.reinhold at oracle.com:
>> The following JEP is proposed to target JDK 11:
>>
>>   330: Launch Single-File Source-Code Programs
>>        http://openjdk.java.net/jeps/330
>>
>> Feedback on this proposal is more than welcome, as are reasoned
>> objections.  If no such objections are raised by 23:00 UTC on Thursday,
>> 24 May, or if they're raised and then satisfactorily answered, then
>> per the JEP 2.0 process proposal [1] I'll target this JEP to JDK 11.
>>
>> - Mark
>>
>>
>> [1] http://cr.openjdk.java.net/~mr/jep/jep-2.0-02.html
>>
>
> I like this proposal.
>
> I have a question about the shebang support though. If I write a
> sourcefile Test.java like this:
>
> #!/usr/bin/java
>
> public class Test {
>     public static void main(String[] args) {
>         System.out.println("Hello");
>     }
> }
>
> ... then it's not a valid Java source file anymore, and (currently)
> rejected by javac. I see that it is not relevant for the intended use
> because the java launcher would strip the first line (except for the
> newline). I still find it odd.
>
> In particular, it may end up confusing for the growing experience:
> - people who start learning Java using this single-source feature will
> find that shebang 'Java scripts' don't actually compile when passed to
> the Java compiler
> - the little Java script turns out to be 'too slow', hey, let's compile
> it. Oops, doesn't work.
> - the little Java scipt has grown to complicated and needs additional
> classes, but doesn't compile.
> - editors/IDEs might (rightly) flag it as errors
>
> etc
>
> I wonder if it might be reasonable to extend the JLS to allow for
> shebang support too? Or maybe even don't extend the JLS but make
> compilers behave nicely anyway? At the very least, there should be some
> language in the JEP that mentions this issue. It is a complication that
> seems more important than the mentioned "HelloWorld"-package with "java"
> classname.
>
> Best regards, Roman
>