mixedJavaRelease compatibility with toolchain

[carl-mastrangelo]

In Gradle 6.8, a new clause called toolchain was introduced that decoupled the JDK used for Gradle itself from the JDK used to compile and run the project's code. One of the limitations of this new clause is that the sourceRelease and targetRelease versions can no longer be set on the (sub)project itself, since it's forbidden by the toolchain. For example this fails:

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(11)
    }

    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

To work around this, the source and target can be set on the JavaCompile tasks directly. For example this works:

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

tasks.withType(JavaCompile) {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

I am trying to use the Java modularity plugin to compile some of my subprojects with lower target compatibilities, but using a more modern toolchain. I would like to use the mixedJavaRelease feature to compile the subproject with JDK 8, but the module-info.java with JDK 9. This works when not using the tool chain, because the source and target compatibility can be set on the factored out Gradle task. However, when using the toolchain, javamodularity tries to set source and target compatibility on the task itself, which Gradle disallows. For example this fails again:

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

tasks.withType(JavaCompile) {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

modularity.mixedJavaRelease 8

[siordache]

Not sure if it works in all situations, but try this:

Replace

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

tasks.withType(JavaCompile) {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

modularity.mixedJavaRelease 8

with

compileJava {
    moduleOptions {
        compileModuleInfoSeparately = true
    }
    javaCompiler = javaToolchains.compilerFor {
        languageVersion = JavaLanguageVersion.of(8)
    }
}

tasks.compileModuleInfoJava {
    javaCompiler = javaToolchains.compilerFor {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

[carl-mastrangelo]

I'm afraid doesn't work. It looks like the main compileJava task still is setting --module-path, likely because I am on Gradle 7, which defaults modularity.inferModulePath on. Disabling that though, runs into another problem: the compileTestJava task still expects the module system to be in place. It is unable to find the the module-info from main:

error: module not found: io.perfmark

[siordache]

I expected that

tasks.compileTestJava {
    modularity.inferModulePath.set(false)
}

would solve the problem, but it doesn't work.

[siordache]

In 1.8.4 I introduced the option compileOnClasspath for the compileTestJava task.
Now it should work if you add this:

tasks.compileTestJava {
    modularity.inferModulePath.set(false)
    moduleOptions {
        compileOnClasspath = true
    }
}

test {
    moduleOptions {
        runOnClasspath = true
    }
}

[carl-mastrangelo]

Thanks! That gets me a lot further. modularity.inferModulePath is still needed but at least I can make progress.

[siordache]

In 1.8.6 the plugin sets modularity.inferModulePath to false, so you should no longer need to do it yourself.

[carl-mastrangelo]

Ok. I ran into other issues (likely my own fault) on this, so we can close this. I'll open another if something comes up.