Gradle multiproject fails to find automatic-module-name with dependency on java-library.

I have a Gradle multi-project build. One subproject (bitcoinj-core) is a Java 7 JAR with an Automatic-Module-Name manifest entry written in the jar task. The other subproject (wallettemplate) has a dependency on the Java 7 module declared as follows:

    implementation project(':bitcoinj-core')

The build fails with the following error:

/path/bitcoinj/wallettemplate/src/main/java/module-info.java:19: error: module not found: org.bitcoinj.core
        requires org.bitcoinj.core;     // Automatic module

Because Gradle detects bitcoinj-core is using the java-library plugin, the wallettemplate compile depends on the “class directory” output of bitcoinj-core, not the jar with the needed manifest entry.

I would like to see one or more of the following solutions:

a. Java Modules Plugin to handle this case gracefully and automatically b. Java Modules Plugin to include documentation or example for how to avoid this problem c. Gradle itself to provide better documentation on this issue and its resolution.

For ©, I’m going to report the issue directly to Gradle.

For the failing build see: https://travis-ci.org/github/msgilligan/bitcoinj/jobs/679852675 This bitcoinj PR (see https://github.com/bitcoinj/bitcoinj/pull/1779) was building correctly until it was rebased on an updated master branch where the bitcoinj-core module had been updated from the Gradle, java plugin to the java-library plugin.

[siordache]

I’m thinking of integrating the above solution in the Java Modules Plugin. It seems pretty safe and, as @jjohannes mentioned, Gradle 6.4 also performs this setting automatically.

[siordache]

I just noticed that @jjohannes also posted a solution, which is most likely the best one:

configurations.compileClasspath.attributes {
   attribute(LibraryElements.LIBRARY_ELEMENTS_ATTRIBUTE, getObjects().named(LibraryElements, LibraryElements.JAR))
}