compileOnlyTest.extendsFrom { compileOnly } is performed too lazily

[jjohannes]

It's done during task configuration for it to be done "late". The reason for that decision was that users may re-configure a test suite between the different modes – WHITEBOX, CLASSPATH, BLACKBOX. And this should only be done for WHITEBOX, which is the default for test sets without module-info.

However, doing it like this may cause the following warning:

Mutating  a configuration after it has been resolved, consumed as a variant, or used for generating published metadata. This behavior has been deprecated. 
  This will fail with an error in Gradle 9.0.
  After a configuration has been observed, it should not be modified.

https://scans.gradle.com/s/ebi3zstoepr22/deprecations?expanded=WyI0Il0

Workaround is to explicitly define the extendsFrom in the build. Then the plugin won't do it again:

configurations.compileOnlyTest { extendsFrom(configurations.compileOnly.get()) }

---

I think the best solution it to add the extendsFrom directly and remove it again on test suite re-configuration.
Code to be adjusted:

java-module-testing/src/main/java/org/gradlex/javamodule/testing/JavaModuleTestingExtension.java

Lines 211 to 215 in a508f05

	Configuration compileOnly = configurations.getByName(sourcesUnderTest.getCompileOnlyConfigurationName());
	Configuration testCompileOnly = configurations.getByName(testSources.getCompileOnlyConfigurationName());
	if (!testCompileOnly.getExtendsFrom().contains(compileOnly)) {
	testCompileOnly.extendsFrom(compileOnly);
	}