[Test] Allow facades to return null which indicates that facade can't complete it's job

This is needed for cases when test pipeline assumes that some part of
  pipeline may be unavailable because of errors on previous stage.

For example, this may occur in some test which check something on IR
  but contains backend facade for compiling binary dependencies. In
  this case testdata with frontend errors is allowed if test has only
  one module which should not be compiled

compiler/test-infrastructure/tests/org/jetbrains/kotlin/test/TestRunner.kt

@@ -98,7 +98,7 @@ class TestRunner(private val testConfiguration: TestConfiguration) {
         if (!frontendKind.shouldRunAnalysis) return
 
         val frontendArtifacts: ResultingArtifact.FrontendOutput<*> = testConfiguration.getFacade(SourcesKind, frontendKind)
-            .transform(module, sourcesArtifact).also { dependencyProvider.registerArtifact(module, it) }
+            .transform(module, sourcesArtifact)?.also { dependencyProvider.registerArtifact(module, it) } ?: return
         val frontendHandlers: List<AnalysisHandler<*>> = testConfiguration.getHandlers(frontendKind)
         for (frontendHandler in frontendHandlers) {
             withAssertionCatching {
@@ -110,7 +110,7 @@ class TestRunner(private val testConfiguration: TestConfiguration) {
         if (!backendKind.shouldRunAnalysis) return
 
         val backendInputInfo = testConfiguration.getFacade(frontendKind, backendKind)
-            .hackyTransform(module, frontendArtifacts).also { dependencyProvider.registerArtifact(module, it) }
+            .hackyTransform(module, frontendArtifacts)?.also { dependencyProvider.registerArtifact(module, it) } ?: return
 
         val backendHandlers: List<AnalysisHandler<*>> = testConfiguration.getHandlers(backendKind)
         for (backendHandler in backendHandlers) {
@@ -120,9 +120,9 @@ class TestRunner(private val testConfiguration: TestConfiguration) {
         for (artifactKind in moduleStructure.getTargetArtifactKinds(module)) {
             if (!artifactKind.shouldRunAnalysis) continue
             val binaryArtifact = testConfiguration.getFacade(backendKind, artifactKind)
-                .hackyTransform(module, backendInputInfo).also {
+                .hackyTransform(module, backendInputInfo)?.also {
                     dependencyProvider.registerArtifact(module, it)
-                }
+                } ?: return
 
             val binaryHandlers: List<AnalysisHandler<*>> = testConfiguration.getHandlers(artifactKind)
             for (binaryHandler in binaryHandlers) {
@@ -167,7 +167,7 @@ private fun <A : ResultingArtifact<A>> AnalysisHandler<A>.processModule(module:
 private fun AbstractTestFacade<*, *>.hackyTransform(
     module: TestModule,
     artifact: ResultingArtifact<*>
-): ResultingArtifact<*> {
+): ResultingArtifact<*>? {
     @Suppress("UNCHECKED_CAST")
     return (this as AbstractTestFacade<ResultingArtifact.Source, ResultingArtifact.Source>)
         .transform(module, artifact as ResultingArtifact<ResultingArtifact.Source>)
@@ -176,7 +176,7 @@ private fun AbstractTestFacade<*, *>.hackyTransform(
 private fun <I : ResultingArtifact<I>, O : ResultingArtifact<O>> AbstractTestFacade<I, O>.transform(
     module: TestModule,
     inputArtifact: ResultingArtifact<I>
-): O {
+): O? {
     @Suppress("UNCHECKED_CAST")
     return transform(module, inputArtifact as I)
 }

compiler/test-infrastructure/tests/org/jetbrains/kotlin/test/model/Facades.kt

@@ -13,7 +13,7 @@ abstract class AbstractTestFacade<I : ResultingArtifact<I>, O : ResultingArtifac
     abstract val inputKind: TestArtifactKind<I>
     abstract val outputKind: TestArtifactKind<O>
 
-    abstract fun transform(module: TestModule, inputArtifact: I): O
+    abstract fun transform(module: TestModule, inputArtifact: I): O?
 
     open val additionalServices: List<ServiceRegistrationData>
         get() = emptyList()