is ClassLoader.loadClass() supposed to work on module-info classes?

[Stephen Felts]

I agree.  I would much rather be able to see the information using unzip -p and update it using a text editor or any tool that can write text.



-----Original Message-----
From: Paul Benedict [mailto:pbenedict at apache.org] 
Sent: Wednesday, December 02, 2015 9:53 AM
To: Remi Forax
Cc: jigsaw-dev at openjdk.java.net
Subject: Re: is ClassLoader.loadClass() supposed to work on module-info classes?

This is probably a good time to (once again) bring up the objection that the Module Descriptor shouldn't be a class file to begin with. I know I am not the only one who has stated this on the mailing list. I doubt this email will gain any traction, but it's something the EG should seriously consider -- as a group. Especially since the Module Descriptor is likely to be read/written by many tools to add custom data, it's clear it's more like a Manifest than a source file.

Cheers,
Paul

On Wed, Dec 2, 2015 at 8:46 AM, Remi Forax <forax at univ-mlv.fr> wrote:

> ----- Mail original -----
> > De: "Alan Bateman" <Alan.Bateman at oracle.com>
> > À: "Stephane Epardaud" <stef at epardaud.fr>, 
> > jigsaw-dev at openjdk.java.net
> > Envoyé: Mercredi 2 Décembre 2015 14:56:00
> > Objet: Re: is ClassLoader.loadClass() supposed to work on 
> > module-info
> classes?
> >
> > On 02/12/2015 11:01, Stephane Epardaud wrote:
> > > Just tried it and got:
> > >
> > > Exception in thread "main" java.lang.ClassFormatError: Illegal 
> > > class name "com.ceylon.java9.Test" in class file module-info
> > >      at java.lang.ClassLoader.defineClass1(java.base at 9.0/Native
> Method)
> > >      at
> > >      java.lang.ClassLoader.defineClass(java.base at 9.0
> /ClassLoader.java:854)
> > >      at
> > > java.security.SecureClassLoader.defineClass(java.base at 9.0
> /SecureClassLoader.java:152)
> > >      at
> > > java.net.URLClassLoader.defineClass(java.base at 9.0
> /URLClassLoader.java:462)
> > >      at
> > > java.net.URLClassLoader.access$100(java.base at 9.0
> /URLClassLoader.java:75)
> > >      at
> > >      java.net.URLClassLoader$1.run(java.base at 9.0
> /URLClassLoader.java:370)
> > >      at
> > >      java.net.URLClassLoader$1.run(java.base at 9.0
> /URLClassLoader.java:364)
> > >      at java.security.AccessController.doPrivileged(java.base at 9.0
> /Native
> > > Method)
> > >      at
> > > java.net.URLClassLoader.findClass(java.base at 9.0
> /URLClassLoader.java:363)
> > >      at java.lang.ClassLoader.loadClass(java.base at 9.0
> /ClassLoader.java:440)
> > >      at java.lang.ClassLoader.loadClass(java.base at 9.0
> /ClassLoader.java:373)
> > >
> > > I know it works for package-info.class files, but is it supposed 
> > > to
> work
> > > with module-info.class files too? Or is it just not implemented yet?
> > >
> > The this_class should be <internal-name>/module-info but in any 
> > case, this isn't the way to "define" a module to the run-time. 
> > Instead modules are defined in layers, with Layer.create the method to create a Layer.
>
> Alan,
> there are two issues, the first one is should a module-info be 
> accessible at runtime as a Class and the second is that the current 
> binary format for a module-info.class break the invariant that the 
> name of the .class is the same as the name inside of the .class 
> because the name used for a module-info.class is the name of the module.
>
> 1) I think module-info should not be reified to a class, defineClass 
> should reject any .class that has a module bit set in the class file format.
>    If we allow to create a Class from a module-info, a class loader 
> may be able to load several module-info.class and it will be a real 
> mess because module-info.class is not qualified in the jar file so the 
> classloader will return the first seen.
> 2) In term of backward compatibility, I think i prefer that the 
> module-info.class uses "module-info" as class name and store the name 
> of the module inside an attribute.
>    An already existing tool that parses the bytecode format may forget 
> to check the class version and use the module name to do something, if 
> the name inside the module-info is "module-info", it will be easier to 
> diagnose because the error will report a failure on "module-info" and 
> not on a name that can also be a package name.
>
> >
> > -Alan.
> >
>
> Rémi
>