[GWT] [ERROR] Hint: Check that your module inherits 'com.google.gwt.core.Core'

[Clint Yang]

Hi all,

I haven't done GWT development for a while and wanted to try again. I installed JDK 12 and Eclipse 2019-03. I installed GWT Eclipse Plugin (GWT 2.8.1). 

From Eclipse, I created a hello world project this way:

1. Click on 'New GWT Application Project'
2.  Project name: Gwt5, Package: com.foo, Use default SDK (GWT 2.8.1)
3. Click on 'GWT Compile Project'

I see this error:

Compiling module com.foo.Gwt5

   [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')

I didn't change my gwt.xml.

Any suggestion?

[Craig Mitchell]

I don't believe GWT supports Java 12 yet.  I'd recommend just using Java 8.

And you might want to use the latest GWT version (2.8.2).

[Christian Nzhie]

Hello here.
I would like to react for this threat. Would at this time (2022) gwt supports java 12?
For I am experiencing the error mentioned above.
Thanks in advance.

[Michael Conrad]

We are using JDK 17 here at the office for builds without any issue. (Gradle setup here).

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[Thomas Broyer]

See https://www.gwtproject.org/release-notes.html#Release_Notes_2_10_0

GWT *runs* on JDKs from 8 to 17; you can however only compile Java 11 –at most– source files (depending on -sourceLevel).

When facing that kind of error, make sure you run with -failOnError (or its older name: -strict), and possibly use a more verbose -logLevel.

[Tiberiu]

Hello everyone,

I just upgraded to GWT 2.10.0 from 2.8.1 and I receive the same error when compiling through an Ant build.

The code and scripts are identical and is compiling just fine with Java 1.8, GWT 2.8.1 and Eclipse 4.17. However with Java 13 or 17, GWT 2.10.0 and Eclipse 4.28 gives the error. Although in the second configuration it compiles successfully through the Eclipse GWT plugin it does not compile using the Ant build. But the GWT module is the same...

What am I missing?

Thanks you,

Tiberiu

[Colin Alworth]

Tiberiu, the fact that it works in Eclipse strongly suggests to me that the ant classpath is different from the eclipse project classpath. That different configuration will lead to different results. This error is typically indicative of some other error happening (typically classpath related) - double check that, and add the "-strict" argument to the Compiler invocation to make sure you see any earlier errors as well (if any).

[Tiberiu]

Thanks Colin! Indeed the Ant classpath was using the old GWT 2.8.1... My bad, sorry.

Tiberiu

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