jmods-less jlinking prototype

[Alan Bateman]

On 15/03/2023 16:57, Severin Gehwolf wrote:
> :
> I'd argue that the case where users actually want things back (add
> back, rather than remove) from any base JDK image is rather small.
> Though, I have no numbers about this so this is only anecdotal. Have
> you seen use-cases doing that (add-back, taking from jmods)?

Almost every usage that I've observed has been reduction and one jlink 
step to create a small run-time image. It's always start with a JDK 
build with packaged modules and then jlink to generate a run-time image 
with the subset of the standard and JDK modules that the application 
needs. Some sightings have included jlink options to compress or strip 
debug attributes, just to get the size down. I haven't seen any usages 
of --keep-packaged-modules so the resulting run-time couldn't be used to 
stamp out another run-time image, at least not without specifying 
-module-path and of course including the jdk.jlink module.

The only of additive case that I've come across is with the GraalVM 
build where they use the jlink --add-option to add VM options to select 
the Graal JIT. This works by adding a resource to the java.base module.  
More recently,  --save-jlink-argfiles has been added so the options are 
preserved for future stamping of out of images. I haven't seen any 
usages of this yet but it would need to be paired with 
--keep-packaged-modules to be useful. Your prototype avoid needing that 
of course.

-Alan