[Gradle] CompletableFuture: Add 'isCompleted' API

^KT-60441 Verification Pending

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/utils/Future.kt

@@ -53,6 +53,7 @@ internal interface LenientFuture<T> : Future<T> {
 }
 
 internal interface CompletableFuture<T> : Future<T> {
+    val isCompleted: Boolean
     fun complete(value: T)
 }
 
@@ -112,6 +113,9 @@ private class FutureImpl<T>(
 ) : CompletableFuture<T>, Serializable {
     fun completeWith(result: Result<T>) = deferred.completeWith(result)
 
+    override val isCompleted: Boolean
+        get() = deferred.isCompleted
+
     override fun complete(value: T) {
         deferred.complete(value)
     }

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/FutureTest.kt

@@ -20,9 +20,7 @@ import org.jetbrains.kotlin.gradle.utils.*
 import org.junit.Test
 import org.junit.jupiter.api.assertThrows
 import java.util.concurrent.atomic.AtomicInteger
-import kotlin.test.assertEquals
-import kotlin.test.assertFailsWith
-import kotlin.test.assertNull
+import kotlin.test.*
 
 class FutureTest {
 
@@ -164,4 +162,21 @@ class FutureTest {
         assertFailsWith<IllegalLifecycleException> { future.getOrThrow() }
         future.await()
     }
+
+    @Test
+    fun `test - future isCompleted`() = project.runLifecycleAwareTest {
+        val future = CompletableFuture<Unit>()
+        assertFalse(future.isCompleted)
+
+        launchInStage(KotlinPluginLifecycle.Stage.AfterFinaliseDsl) {
+            assertFalse(future.isCompleted)
+            future.complete(Unit)
+            assertTrue(future.isCompleted)
+        }
+
+        launch {
+            future.await()
+            assertTrue(future.isCompleted)
+        }
+    }
 }