How do I resolve this No matching variant problem

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1

Recently updated to Gradle 7.2 and have been updating a library hierarchy where each library in the hierarchy includes this configuration:

tasks.withType(JavaCompile).configureEach {
    javaCompiler = javaToolchains.compilerFor {
        languageVersion = JavaLanguageVersion.of( 11 )
    }
}

tasks.withType(Test).configureEach {
    javaLauncher = javaToolchains.launcherFor {
        languageVersion = JavaLanguageVersion.of( 11 )
    }
}

tasks.compileJava {
    sourceCompatibility = "${JavaVersion.VERSION_1_8}"
}

ā€¦which I chose based on this recommendation. Basically, Iā€™m using jdk 11 to compile due to licensing, but am not using any language features beyond 8, and have no reason to require 11 source compatibility in dependents.

I have a library dependency hierarchy like so:

lib-0 ā† lib-1 ā† lib-2 ā† lib 3

ā€¦where each of these libraries is under our control and <- indicates that the library on the right depends on the library on the left.

Every project, from lib-0 up to lib-2 builds without error and then, for some reason I do not understand, lib-3 generates this error:

> Could not resolve all files for configuration ':compileClasspath'.
   > Could not resolve org.acme.nimbus:lib-2:3.0.0.+.
     Required by:
         project :
      > No matching variant of org.acme.nimbus:lib-2:3.0.0.8 was found. The consumer was configured to find an API of a library compatible with Java 8, preferably in the form of class files, preferably optimized for standard JVMs, and its dependencies declared externally but:
          - Variant 'apiElements' capability org.acme.nimbus:lib-2:3.0.0.8 declares an API of a library, packaged as a jar, and its dependencies declared externally:
              - Incompatible because this component declares a component compatible with Java 11 and the consumer needed a component compatible with Java 8
              - Other compatible attribute:
                  - Doesn't say anything about its target Java environment (preferred optimized for standard JVMs)
          - Variant 'runtimeElements' capability org.acme.nimbus:lib-2:3.0.0.8 declares a runtime of a library, packaged as a jar, and its dependencies declared externally:
              - Incompatible because this component declares a component compatible with Java 11 and the consumer needed a component compatible with Java 8
              - Other compatible attribute:
                  - Doesn't say anything about its target Java environment (preferred optimized for standard JVMs)

I donā€™t understand why the lib-3 project is the first to complain like this, when all of the libraries have the exact same compile and source compatibility configuration. I canā€™t find anything special or different about lib-2 compared to the other library projects that would cause a problem for lib-3.

Also, I donā€™t understand what I need to do in order to remove this incompatibility. Iā€™ve been through this documentation, and more or less understand how itā€™s working, but I donā€™t understand how to control what variants are getting exposed to change the outcome.

Any assistance is very much appreciated.

What exactly does this clue mean: Incompatible because this component declares a component compatible with Java 11?

ā€¦is it saying that lib-2 is exposing one of its dependencies via its api configuration, and that dependency is causing the problem? How do I find out which one?

2

Found the problem - this was a lib-3 problem with an older gradle wrapper version. Updating to the latest fixed all the things.

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