[Gradle] Add expected K2 Kapt fallback warning

#KT-60588 In Progress

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

@@ -69,7 +69,9 @@ class BuildCacheRelocationIT : KGPBaseTest() {
             secondProject,
             listOf(":classes", ":testClasses"),
             listOf(":kaptKotlin", ":kaptGenerateStubsKotlin", ":compileKotlin", ":compileTestKotlin", ":compileJava")
-        )
+        ) {
+            assertNoBuildWarnings(expectedK2KaptWarnings)
+        }
     }
 
     @JsGradlePluginTests
@@ -294,16 +296,19 @@ class BuildCacheRelocationIT : KGPBaseTest() {
         firstProject: TestProject,
         secondProject: TestProject,
         tasksToExecute: List<String>,
-        cacheableTasks: List<String>
+        cacheableTasks: List<String>,
+        additionalAssertions: BuildResult.() -> Unit = {},
     ) {
         firstProject.build(*tasksToExecute.toTypedArray()) {
             assertTasksPackedToCache(*cacheableTasks.toTypedArray())
+            additionalAssertions()
         }
 
         firstProject.build("clean")
 
         secondProject.build(*tasksToExecute.toTypedArray()) {
             assertTasksFromCache(*cacheableTasks.toTypedArray())
+            additionalAssertions()
         }
     }
 

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

@@ -76,6 +76,7 @@ class BuildServiceDeclarationIT : KGPBaseTest() {
             enableStableConfigurationCachePreview()
             build("build") {
                 assertOutputDoesNotContainBuildServiceDeclarationWarnings()
+                assertNoBuildWarnings(expectedK2KaptWarnings)
             }
         }
     }

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

@@ -70,6 +70,7 @@ class UnnamedTaskInputsIT : KGPBaseTest() {
 
             build("assemble") {
                 assertNoUnnamedInputsOutputs()
+                assertNoBuildWarnings(expectedK2KaptWarnings)
             }
         }
     }

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

@@ -172,6 +172,11 @@ fun BuildResult.assertNoBuildWarnings(
     }
 }
 
+val expectedK2KaptWarnings = setOf(
+    "w: [InternalKotlinGradlePluginPropertiesUsed | WARNING] ATTENTION! This build uses the following Kotlin Gradle Plugin properties:",
+    "w: Kapt currently doesn't support language version 2.0+. Falling back to 1.9."
+)
+
 /**
  * Asserts compilation is running via Kotlin daemon with given jvm arguments.
  */

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kapt2/simple/build.gradle

@@ -19,5 +19,5 @@ dependencies {
 }
 
 tasks.named("compileKotlin", KotlinJvmCompile) {
-    compilerOptions.allWarningsAsErrors = true
+    compilerOptions.allWarningsAsErrors = false // compilation with LV=2.0 prints warning about kapt fallback
 }