Fix generic signature of FunctionN type visible from Java

compiler/backend/src/org/jetbrains/kotlin/codegen/state/KotlinTypeMapper.java

@@ -651,17 +651,21 @@ public class KotlinTypeMapper {
         List<TypeParameterDescriptor> parameters = classDescriptor.getDeclaredTypeParameters();
         List<TypeProjection> arguments = type.getArguments();
 
-        if (classDescriptor instanceof FunctionClassDescriptor &&
-            ((FunctionClassDescriptor) classDescriptor).getFunctionKind() == FunctionClassDescriptor.Kind.KFunction) {
-            // kotlin.reflect.KFunction{n}<P1, ... Pn, R> is mapped to kotlin.reflect.KFunction<R> on JVM (see JavaToKotlinClassMap).
-            // So for these classes, we need to skip all type arguments except the very last one
-            writeGenericArguments(
-                    signatureVisitor,
-                    Collections.singletonList(CollectionsKt.last(arguments)),
-                    Collections.singletonList(CollectionsKt.last(parameters)),
-                    mode
-            );
-            return;
+        if (classDescriptor instanceof FunctionClassDescriptor) {
+            FunctionClassDescriptor functionClass = (FunctionClassDescriptor) classDescriptor;
+            if (functionClass.hasBigArity() ||
+                functionClass.getFunctionKind() == FunctionClassDescriptor.Kind.KFunction) {
+                // kotlin.reflect.KFunction{n}<P1, ..., Pn, R> is mapped to kotlin.reflect.KFunction<R> (for all n), and
+                // kotlin.Function{n}<P1, ..., Pn, R> is mapped to kotlin.jvm.functions.FunctionN<R> (for n > 22).
+                // So for these classes, we need to skip all type arguments except the very last one
+                writeGenericArguments(
+                        signatureVisitor,
+                        Collections.singletonList(CollectionsKt.last(arguments)),
+                        Collections.singletonList(CollectionsKt.last(parameters)),
+                        mode
+                );
+                return;
+            }
         }
 
         writeGenericArguments(signatureVisitor, arguments, parameters, mode);

compiler/testData/codegen/box/functions/bigArity/callFromJava.kt

@@ -0,0 +1,36 @@
+// !LANGUAGE: +FunctionTypesWithBigArity
+// WITH_RUNTIME
+// TARGET_BACKEND: JVM
+// FILE: J.java
+
+import kotlin.jvm.functions.FunctionN;
+
+public class J {
+    public static String test() {
+        return KKt.call(new FunctionN<String>() {
+            @Override
+            public String invoke(Object... args) {
+                if (args.length != getArity()) throw new IllegalArgumentException("Incorrect arity: " + args.length);
+
+                return ((A) args[5]).getMessage() +
+                        ((A) args[28]).getMessage();
+            }
+
+            @Override
+            public int getArity() {
+                return 30;
+            }
+        });
+    }
+}
+
+// FILE: K.kt
+
+class A(val message: String)
+
+fun call(f: (A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A) -> String): String {
+    val a = A("XXX")
+    return f(a, a, a, a, a, A("O"), a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, a, A("K"), a)
+}
+
+fun box(): String = J.test()

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -10623,6 +10623,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/functions/bigArity"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
             }
 
+            @TestMetadata("callFromJava.kt")
+            public void testCallFromJava() throws Exception {
+                runTest("compiler/testData/codegen/box/functions/bigArity/callFromJava.kt");
+            }
+
             @TestMetadata("callWithIncorrectNumberOfArguments.kt")
             public void testCallWithIncorrectNumberOfArguments() throws Exception {
                 runTest("compiler/testData/codegen/box/functions/bigArity/callWithIncorrectNumberOfArguments.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -10628,6 +10628,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/functions/bigArity"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
             }
 
+            @TestMetadata("callFromJava.kt")
+            public void testCallFromJava() throws Exception {
+                runTest("compiler/testData/codegen/box/functions/bigArity/callFromJava.kt");
+            }
+
             @TestMetadata("callWithIncorrectNumberOfArguments.kt")
             public void testCallWithIncorrectNumberOfArguments() throws Exception {
                 runTest("compiler/testData/codegen/box/functions/bigArity/callWithIncorrectNumberOfArguments.kt");

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -10623,6 +10623,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/functions/bigArity"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM_IR, true);
             }
 
+            @TestMetadata("callFromJava.kt")
+            public void testCallFromJava() throws Exception {
+                runTest("compiler/testData/codegen/box/functions/bigArity/callFromJava.kt");
+            }
+
             @TestMetadata("callWithIncorrectNumberOfArguments.kt")
             public void testCallWithIncorrectNumberOfArguments() throws Exception {
                 runTest("compiler/testData/codegen/box/functions/bigArity/callWithIncorrectNumberOfArguments.kt");