import static org.junit.Assume.assumeFalse
import static org.junit.Assume.assumeTrue

@TargetVersions("5.0+")
class ProjectTheExtensionCrossVersionSpec extends CrossVersionIntegrationSpec {

    def "can access extensions and conventions with current Gradle version from plugin built with Gradle 5.0+"() {

        def isFlaky = OperatingSystem.current().isWindows() &&
            previous.version >= GradleVersion.version("6.5") &&

import org.gradle.declarative.dsl.evaluation.InterpretationSequence
import org.gradle.groovy.scripts.ScriptSource
import org.gradle.internal.declarativedsl.conventions.softwareTypeRegistryBasedConventionRegistrar
import org.gradle.internal.declarativedsl.conventions.softwareTypeRegistryBasedConventionRepository
import org.gradle.internal.declarativedsl.evaluator.runner.EvaluationResult.NotEvaluated

  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional
  optional .k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // Specification of the desired behavior of a cron job, including the schedule.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
  // +optional
  optional CronJobSpec spec = 2;

            ?: Factory {
                // Find convention
                // Reflective look up to still support plugins that inlined this function once conventions will be removed
                this::class.java.methods.firstOrNull { it.name == "getConvention" }?.invoke(this)?.let { convention ->
                    convention::class.java.getMethod("findPlugin", Class::class.java).invoke(convention, T::class.java)
                }

By sticking to the default conventions, new developers to the project immediately know how to find their way around.
While those conventions can be reconfigured, it makes it harder to build script users and authors to manage the build logic and its outcome.
Try to stick to the default conventions as much as possible except if you need to adapt to the layout of a legacy project.

  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // Specification of the desired behavior of a cron job, including the schedule.
  // More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
  // +optional
  optional CronJobSpec spec = 2;

    val conventions: List<ProjectSchemaEntry<TypeOf<*>>>,
    val tasks: List<ProjectSchemaEntry<TypeOf<*>>>,
    val containerElements: List<ProjectSchemaEntry<TypeOf<*>>>
)


internal
fun targetSchemaFor(target: Any, targetType: TypeOf<*>): TargetTypedSchema {

    val extensions = mutableListOf<ProjectSchemaEntry<TypeOf<*>>>()
    val conventions = mutableListOf<ProjectSchemaEntry<TypeOf<*>>>()

    val extensions: List<ProjectSchemaEntry<T>>,
    val conventions: List<ProjectSchemaEntry<T>>,
    val tasks: List<ProjectSchemaEntry<T>>,
    val containerElements: List<ProjectSchemaEntry<T>>,
    val configurations: List<ConfigurationEntry<String>>,
    val scriptTarget: Any? = null
) {

    fun <U> map(f: (T) -> U) = ProjectSchema(
        extensions.map { it.map(f) },
        conventions.map { it.map(f) },
        tasks.map { it.map(f) },

        setup:
        file('included/settings.gradle').text = """
            pluginManagement {
                includeBuild('../conventions')
            }
            plugins {
                id 'script-plugin'
            }
            include('sub')
        """
        file('conventions/settings.gradle') << """
        """

Concretely, we add a _convention plugin_ in `buildSrc` to share the integration test setup between multiple subprojects:

====
include::sample[dir="kotlin",files="buildSrc/src/main/kotlin/myproject.java-conventions.gradle.kts[]"]
include::sample[dir="groovy",files="buildSrc/src/main/groovy/myproject.java-conventions.gradle[]"]
====

And apply it in an application project:

====