[11u] Desupport building with Java 10?

[Lindenmaier, Goetz]

> Do you have some data were it is *indeed* a lot of effort?
It is not a lot of effort for a single change, but it keeps popping 
up. I can't find the changes in question currently. I think I had 
to handle three in the 11.0.14/15 releases. 

If we want to support building with 10 we should use a jdk10 in the 
GHA builds to detect issues early.  At least for one platform, 
probably linuxx86_64 dbg build.  Currently it's temurin-11.0.12
everywhere.

Best regards,
  Goetz.

> -----Original Message-----
> From: Severin Gehwolf <sgehwolf at redhat.com>
> Sent: Thursday, February 17, 2022 10:57 AM
> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; jdk-updates-
> dev at openjdk.java.net
> Subject: Re: [11u] Desupport building with Java 10?
> 
> On Thu, 2022-02-17 at 08:04 +0000, Lindenmaier, Goetz wrote:
> > Hi,
> >
> > OpenJDK has the policy that each jdk should be able to
> > be bootstrapped with the previous Java version.
> > See also DEFAULT_ACCEPTABLE_BOOT_VERSIONS [1].
> > This makes sense for new Java versions but not for
> > updates of LTSes.
> 
> Why not?
> 
> >  For jdk11u, using a Java 10 jdk
> > for bootstrapping even is a security issue as there
> > is no maintained jdk10.
> 
> I'm not sure I'm bying the security argument for the bootstrap process.
> 
> > On the other side we had to fix a few changes in
> > the past to work with Java 10.  We should avoid this
> > effort.
> 
> In the past getting this to work wasn't a lot of effort. Do you have
> some data were it is *indeed* a lot of effort?
> 
> > I propose to give up supporting Java 10 in the build
> > in 11.0.16 and to change DEFAULT_ACCEPTABLE_BOOT_VERSIONS
> > accordingly.
> >
> > If there are no objections I'll do the corresponding
> > change for 11.0.16.
> 
> This isn't a good idea. It breaks the bootstrap chain. Unless there are
> good cases where the "cost of maintaining JDK 10 bootstrap support" >>>
> "benefit of being able to bootstrap the latest JDK 11", I'm against it.
> 
> Thanks,
> Severin