Problem compiling GWT code with Java9

At Labkey.com we're trying to compile all of our code, which includes GWT code, with Java9 (due for release in the summer)....getting a head start. We have not been able to compile GWT code, which doesn't use any new Java features. We're getting the error

     [java] Compiling module org.labkey.experiment.property.Designer

     [java]    [ERROR] Unable to find type 'java.lang.Object'

     [java]       [ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core' either directly or indirectly (most often by inheriting module 'com.google.gwt.user.User')

We've had an older version of GWT but have tried with the latest 2.8 as well and get the same thing. I've added -logLevel=DEBUG to get more info and the log says we're inheriting all of the appropriate packages, including com.google.gwt.core.Core and com.google.gwt.emul.Emulation, which of course is where java.lang.Object lives. It seems like something is going wrong with gwt-unitCache because the log looks like this:

..........lots of inherits before this..........

     [java]       Module location: file:/Users/davebradlee/trunk/server/internal/gwtsrc/org/labkey/api/gwt/Internal.gwt.xml

     [java]       Loading inherited module 'com.extjs.gxt.ui.GXT'

     [java]          Module location: jar:file:/Users/davebradlee/trunk/external/lib/build/gxt.jar!/com/extjs/gxt/ui/GXT.gwt.xml

     [java]          Loading inherited module 'com.google.gwt.json.JSON'

     [java]             Module location: jar:file:/Users/davebradlee/trunk/external/lib/build/gwt-user.jar!/com/google/gwt/json/JSON.gwt.xml

     [java]       Loading inherited module 'com.allen_sauer.gwt.dnd.gwt-dnd'

     [java]          Module location: jar:file:/Users/davebradlee/trunk/external/lib/server/gwt-dnd-3.2.0.jar!/com/allen_sauer/gwt/dnd/gwt-dnd.gwt.xml

     [java] Public resources found in...

     [java] Translatable source found in...

     [java] Persistent unit cache dir set to: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache

     [java] Opening cache file: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache/gwt-unitCache-6a094daf5d20bb65adf2d207cc48308bde849f64-0000015A3E41072B

     [java] Looking for previously cached Compilation Units in /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache

     [java] Compiling module org.labkey.experiment.property.Designer

     [java]    Found 0 cached/archived units.  Used 0 / 0 units from cache.

     [java]    Compiling...

     [java]       Compilation completed in 0.00 seconds

     [java]    PersistentUnitCache cleanup requested

     [java]    Added 0 units to PersistentUnitCache since last cleanup

     [java]    Skipped PersistentUnitCache because no units were added

     [java]    Removing invalidated units

     [java]    Resolving enclosing classes

     [java]    Tracing compile failure path for type 'java.lang.Object'

     [java]       Checked 0 dependencies for errors.

     [java]    [ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core' either directly or indirectly (most often by inheriting module 'com.google.gwt.user.User')

     [java] Closing cache file: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache/gwt-unitCache-6a094daf5d20bb65adf2d207cc48308bde849f64-0000015A3E41072B (0 units written)

     [java] Deleting empty file: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache/gwt-unitCache-6a094daf5d20bb65adf2d207cc48308bde849f64-0000015A3E41072B

     [java] Shutting down PersistentUnitCache thread

Using Java8 the log looks like this

.......

     [java] Persistent unit cache dir set to: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache

     [java] Opening cache file: /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache/gwt-unitCache-6a094daf5d20bb65adf2d207cc48308bde849f64-0000015A3E53CB49

     [java] Looking for previously cached Compilation Units in /Users/davebradlee/trunk/build/modules/experiment/explodedModule/gwt-unitCache

     [java] Compiling module org.labkey.experiment.property.Designer

     [java]    Found 0 cached/archived units.  Used 0 / 3794 units from cache.

     [java]    Compiling...

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       60% complete (ETR: 3 seconds)

     [java]       70% complete (ETR: 2 seconds)

     [java]       80% complete (ETR: 2 seconds)

     [java]       90% complete (ETR: 1 seconds)

     [java]       100% complete (ETR: 0 seconds)

     [java]       Compilation completed in 10.80 seconds

     [java]    PersistentUnitCache cleanup requested

     [java]    Added 3794 units to PersistentUnitCache since last cleanup

Anyway, has anyone else tried to compile GWT code with Java9? Or any ideas how we might make the compiler happy?

Thanks!

-- Dave

--
You received this message because you are subscribed to the Google Groups "GWT Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to google-web-toolkit+unsubscribe@googlegroups.com.
To post to this group, send email to google-web-toolkit@googlegroups.com.
Visit this group at https://groups.google.com/group/google-web-toolkit.
For more options, visit https://groups.google.com/d/optout.