Let's take the warnings for one module, c.g.c.base.testModule, as an example:

              [INFO] Validating units:
              [INFO]    Ignored 53 units with compilation errors in first pass.
              [INFO] Compile with -strict or with -logLevel set to TRACE or DEBUG to see all errors.

            Turning up the log level, we see that GWT is trying to compile classes from other

  <scope name="IDE" pattern="file[idea_main]:*/||file[idea]:testData/*/||file[idea-formatter_main]:*/||file[ide-common_main]:*/||file[idea-android_main]:*/||file[idea-android-output-parser_main]:*/||file[idea]:idea-completion/testData/*/||file[idea-core_main]:*/||file[idea-gradle_main]:*/||file[idea-jps-common_main]:*/||file[idea-jvm_main]:*/||file[idea]:idea-live-templates/src/*/||file[idea]:idea-live-templates/testData/*/||file[idea-maven_main]:*/||file[idea-repl]...

    <dependency>
      <groupId>org.apache.maven.its.mng4003</groupId>
      <artifactId>d</artifactId>
      <version>1</version>
    </dependency>
  </dependencies>

  <build>
    <!-- NOTE: The combination with a plugin management section is an essential part of the test -->
    <pluginManagement>
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>2.3</version>

    <dependency>
      <groupId>org.apache.maven.its.mng4003</groupId>
      <artifactId>d</artifactId>
      <version>1</version>
    </dependency>
  </dependencies>

  <build>
    <!-- NOTE: The combination with a plugin section is an essential part of the test -->
    <plugins>
      <plugin>
        <artifactId>maven-clean-plugin</artifactId>
        <version>2.3</version>
      </plugin>
    </plugins>
  </build>

                     be passed as part of the same <arg> as -Xplugin:ErrorProne,
                     and I gave up trying to figure out how to do that for test
                     compilation only. -->
                <arg>-Xplugin:ErrorProne -Xep:NullArgumentForNonNullParameter:OFF -Xep:Java8ApiChecker:ERROR</arg>

            <![CDATA[
            The scope of the dependency - {@code compile}, {@code runtime},
            {@code test}, {@code system}, and {@code provided}. Used to
            calculate the various classpaths used for compilation, testing, and so on.
            It also assists in determining which artifacts to include in a distribution of
            this project. For more information, see

          <version>1.1.0+</version>
          <description>Information for each sub-artifact available in this artifact snapshot. This is only the most recent SNAPSHOT for each unique extension/classifier combination.</description>
          <association>
            <type>SnapshotVersion</type>
            <multiplicity>*</multiplicity>
          </association>
        </field>
      </fields>
      <codeSegments>