[K2] Run Gradle integration tests

Author: vmishenev

dokka-integration-tests/gradle/src/main/kotlin/org/jetbrains/dokka/it/gradle/AbstractGradleIntegrationTest.kt

@@ -41,6 +41,12 @@ public abstract class AbstractGradleIntegrationTest : AbstractIntegrationTest()
                     buildVersions.androidGradlePluginVersion?.let { androidVersion ->
                         "-Pdokka_it_android_gradle_plugin_version=$androidVersion"
                     },
+                    // property flag to use K2
+                    if (TestEnvironment.shouldUseK2())
+                        "-P${TestEnvironment.TRY_K2}=true"
+                    else
+                        null,
+
                     * arguments
                 )
             ).run { this as DefaultGradleRunner }

dokka-integration-tests/gradle/src/main/kotlin/org/jetbrains/dokka/it/gradle/TestEnvironment.kt

@@ -5,9 +5,20 @@
 package org.jetbrains.dokka.it.gradle
 
 public object TestEnvironment {
+    public const val TRY_K2: String = "org.jetbrains.dokka.experimental.tryK2"
+
     public val isExhaustive: Boolean = checkNotNull(System.getenv("isExhaustive")) {
         "Missing `isExhaustive` environment variable"
     }.toBoolean()
+
+    /**
+     * By default, it is disabled
+     */
+    public fun shouldUseK2(): Boolean = getBooleanProperty(TRY_K2)
+
+    private fun getBooleanProperty(propertyName: String): Boolean {
+        return System.getProperty(propertyName) in setOf("1", "true")
+    }
 }
 
 /**