RFR: JDK-8189094: Change required boot jdk to JDK 9

Magnus Ihse Bursie magnus.ihse.bursie at oracle.com
Tue Oct 17 11:10:38 UTC 2017

On 2017-10-16 15:12, Erik Joelsson wrote:
> With JDK 9 released, it's high time to change the required boot jdk 
> for building JDK 10. This time, the change wasn't as straight forward 
> as it usually is.
> It's currently possible to use any of JDK 8, 9 or a recent build of 10 
> to boot the JDK 10 build. This support is however fragile. The most 
> sensitive part is the building and running of the interim javac and 
> javadoc tools, where we build the new JDK 10 versions of these tools, 
> but -source/-target set appropriate for the boot jdk, so we can run 
> them on the boot jdk when compiling the rest of the product.
> In the current build, we compile the java source files of the modules 
> java.compiler, jdk.compiler, jdk.javadoc and jdk.jdeps in the legacy 
> way, using -Xbootclasspath and not including any module-info.java 
> files. We then run them by using the --patch-module argument. This 
> means we are running the JDK 10 classes but using the module 
> definitions of the boot jdk. This works for now, but when the JDK 
> module definitions for any of these modules need to change, this model 
> will start to break.
> In this patch I have tried to change this so we compile and run using 
> JDK 9 module style modes. The big problem to overcome then is that 
> jdk.compiler, and jdk.javadoc are not upgradeable. This means we can't 
> compile new versions of these modules and override them in the boot 
> jdk. This leaves us with two options: either run the interim classes 
> in the unnamed module, or define a new set of interim modules, based 
> on the existing modules but with new names. The first option seems 
> simpler, but that would require maintaining legacy service provider 
> definitions for these modules. So I chose the latter instead. The new 
> module names have ".interim" as suffix.
> To generate the new modules, I copy the module-info.java files to a 
> new gensrc dir and sed replace the module names. I also generate a new 
> ToolProvider.java so that the default tools are taken from the interim 
> modules.
> I've made sure that jrtfs.jar is generated with --release 8 to keep 
> compatibility with JDK 8.
> Webrev: http://cr.openjdk.java.net/~erikj/8189094/webrev.01

This is a quite complex change. It's a bit unfortunate that we have to 
make these kinds of changes to use JDK 9 as a boot JDK. Anyway, that's 
the way it is.

A couple of remarks:

* In boot-jdk.m4, please update the comment as well:

    # When compiling code to be executed by the Boot JDK, force jdk8 compatibility.
- BOOT_JDK_SOURCETARGET="-source 8 -target 8"
+ BOOT_JDK_SOURCETARGET="-source 9 -target 9"

* In JavaCompilation.gmk:

+ # exist yet, is in it.
+ $$(foreach d,$$($1_SRC), \

You can add a space after the comma with no ill effects.

- $$(eval $$(call FillCacheFind,$$($1_SRC)))
+ $$(eval $$(call FillCacheFind, $$(wildcard $$($1_SRC))))

Should not the $(wildcard) filtering be done in the FillCacheFind 
function? It seems reasonable that it should not complain with an error 
if you give it a non-existing directory.

- $1_ALL_SRCS += $$(foreach s, $$($1_SRC), $$(call CacheFind, $$(s)))
+ $1_ALL_SRCS += $$($1_EXTRA_FILES) $$(foreach s, $$($1_SRC), $$(if 
$$(wildcard $$s), \
+ $$(call CacheFind, $$s)))

The same goes here. Any wildcard filtering should be done in CacheFind, 
I think.

* In spec.gmk.in, the code for INTERIM_LANGTOOLS_MODULES_COMMA is 
basically repeating the pre-existing macro CommaList. However, that is 
only available in MakeBase.gmk. I'm not sure it's possible to use, but 
maybe. It looks like there's a lot of hard-coded stuff in spec.gmk.in, 
and maybe that is not the right place for it. Where are  

* In jib-profiles.js:
You have no "var" declaration for the new boot_jdk_version etc. I'm not 
too well-versed in javascript and it is probably quite legal not to, but 
I think it's better style at least to keep it.

* Finally, $(BUILDTOOLS_OUTPUTDIR)/override_modules should be renamed 


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