FIC: Make SAM conversions also for fun interfaces, add base test

compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SamConversionResolverImpl.kt

@@ -16,8 +16,8 @@
 
 package org.jetbrains.kotlin.load.java.sam
 
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.load.java.components.SamConversionResolver
-import org.jetbrains.kotlin.load.java.descriptors.JavaClassDescriptor
 import org.jetbrains.kotlin.storage.StorageManager
 import org.jetbrains.kotlin.types.SimpleType
 
@@ -25,9 +25,9 @@ class SamConversionResolverImpl(
         storageManager: StorageManager,
         private val samWithReceiverResolvers: Iterable<SamWithReceiverResolver>
 ): SamConversionResolver {
-    private val functionTypesForSamInterfaces = storageManager.createCacheWithNullableValues<JavaClassDescriptor, SimpleType>()
+    private val functionTypesForSamInterfaces = storageManager.createCacheWithNullableValues<ClassDescriptor, SimpleType>()
 
-    override fun resolveFunctionTypeIfSamInterface(classDescriptor: JavaClassDescriptor): SimpleType? {
+    override fun resolveFunctionTypeIfSamInterface(classDescriptor: ClassDescriptor): SimpleType? {
         return functionTypesForSamInterfaces.computeIfAbsent(classDescriptor) {
             val abstractMethod = SingleAbstractMethodUtils.getSingleAbstractMethodOrNull(classDescriptor) ?: return@computeIfAbsent null
             val shouldConvertFirstParameterToDescriptor = samWithReceiverResolvers.any { it.shouldConvertFirstSamParameterToReceiver(abstractMethod) }

compiler/frontend.java/src/org/jetbrains/kotlin/load/java/sam/SingleAbstractMethodUtils.java

@@ -78,9 +78,12 @@ public class SingleAbstractMethodUtils {
         // e.g. samType == Comparator<String>?
 
         ClassifierDescriptor classifier = samType.getConstructor().getDeclarationDescriptor();
-        if (classifier instanceof JavaClassDescriptor) {
+        if (classifier instanceof ClassDescriptor) {
+            ClassDescriptor descriptor = (ClassDescriptor) classifier;
+            if (!(descriptor instanceof JavaClassDescriptor) && !descriptor.isFun()) return null;
+
             // Function2<T, T, Int>
-            SimpleType functionTypeDefault = samResolver.resolveFunctionTypeIfSamInterface((JavaClassDescriptor) classifier);
+            SimpleType functionTypeDefault = samResolver.resolveFunctionTypeIfSamInterface(descriptor);
 
             if (functionTypeDefault != null) {
                 SimpleType noProjectionsSamType = SingleAbstractMethodUtilsKt.nonProjectionParametrization(samType);
@@ -131,7 +134,7 @@ public class SingleAbstractMethodUtils {
     }
 
     @Nullable
-    public static FunctionDescriptor getSingleAbstractMethodOrNull(@NotNull JavaClassDescriptor klass) {
+    public static FunctionDescriptor getSingleAbstractMethodOrNull(@NotNull ClassDescriptor klass) {
         // NB: this check MUST BE at start. Please do not touch until following to-do is resolved
         // Otherwise android data binding can cause resolve re-entrance
         // For details see KT-18687, KT-16149
@@ -140,7 +143,13 @@ public class SingleAbstractMethodUtils {
             return null;
         }
 
-        if (klass.isDefinitelyNotSamInterface()) return null;
+        if (klass instanceof JavaClassDescriptor) {
+            if (((JavaClassDescriptor) klass).isDefinitelyNotSamInterface()) {
+                return null;
+            }
+        } else if (!klass.isFun()) {
+            return null;
+        }
 
         List<CallableMemberDescriptor> abstractMembers = getAbstractMembers(klass);
         if (abstractMembers.size() == 1) {
@@ -224,6 +233,9 @@ public class SingleAbstractMethodUtils {
     }
 
     public static boolean isSamType(@NotNull KotlinType type) {
+        ClassifierDescriptor descriptor = type.getConstructor().getDeclarationDescriptor();
+        if (descriptor instanceof ClassDescriptor && ((ClassDescriptor) descriptor).isFun()) return true;
+
         return getFunctionTypeForSamType(type, SamConversionResolver.JavaBasedSamConversionResolver.INSTANCE) != null;
     }