RFR[XS] 8191374 Improve error message when CDS is not supported on exploded build

[Jiangli Zhou]

Looks good.

Thanks,
Jiangli

> On Dec 14, 2017, at 2:30 PM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> Hi, please review this very simple fix for JDK 11:
> 
> https://bugs.openjdk.java.net/browse/JDK-8191374
> http://cr.openjdk.java.net/~iklam/jdk11/8191374-exploded-build-dump-error-msg.v01/
> 
> Summary - the error message is changed to be more obvious what's going on.
> 
> 
> Testing: since we don't have automated tests for exploded builds, I just did some
> manually testing on Linux using the "exploded build", ./jdk/bin/java, which is an
> intermediate file created by the JDK build system.
> 
> 
> Before:
> 
>     $ ./jdk/bin/java -Xshare:dump
>     Error: non-empty directory '/jdk/bld/opencds/jdk/modules/java.base'
>     Hint: enable -Xlog:class+path=info to diagnose the failure
>     Error occurred during initialization of VM
>     CDS allows only empty directories in archived classpaths
> 
> 
> After:
> 
>     $ ./jdk/bin/java -Xshare:dump
>     Error occurred during initialization of VM
>     CDS is not supported in exploded JDK build
> 
> 
> Thanks
> - Ioi