Deal with unnamed Gradle inputs/outputs

Fix the only unnamed input added to a Gradle task at runtime.
Add a test that checks for unnamed task inputs.

Issue #KT-23085 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KotlinGradlePluginIT.kt

@@ -729,4 +729,30 @@ class KotlinGradleIT: BaseGradleIT() {
             }
         }
     }
+
+    @Test
+    fun testNoUnnamedInputsOutputs() {
+        // Use a new Gradle version to enable the usage of the input/output builders, which are new API:
+        val gradleVersionRequirement = GradleVersionRequired.AtLeast("4.4")
+
+        val projects = listOf(
+            Project("simpleProject", gradleVersionRequirement),
+            Project("kotlin2JsProject", gradleVersionRequirement),
+            Project("multiplatformProject", gradleVersionRequirement),
+            Project("simple", gradleVersionRequirement, "kapt2")
+        )
+
+        projects.forEach {
+            it.apply {
+                // Enable caching to make sure Gradle reports the task inputs/outputs during key construction:
+                val options = defaultBuildOptions().copy(withBuildCache = true)
+                build("assemble", options = options) {
+                    // Check that all inputs/outputs added at runtime have proper names
+                    // (the unnamed ones are listed as $1, $2 etc.):
+                    assertNotContains("Appending inputPropertyHash for '\\$\\d+'".toRegex())
+                    assertNotContains("Appending outputPropertyName to build cache key: \\$\\d+".toRegex())
+                }
+            }
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinPlugin.kt

@@ -690,7 +690,9 @@ internal fun configureJavaTask(kotlinTask: KotlinCompile, javaTask: AbstractComp
     // Make Gradle check if the javaTask is up-to-date based on the Kotlin classes
     javaTask.inputsCompatible.run {
         if (isBuildCacheSupported()) {
-            dir(kotlinTask.destinationDir).withNormalizer(CompileClasspathNormalizer::class.java)
+            dir(kotlinTask.destinationDir)
+                .withNormalizer(CompileClasspathNormalizer::class.java)
+                .withPropertyName("${kotlinTask.name} output classes")
         }
         else {
             dirCompatible(kotlinTask.destinationDir)