Use non-allowed actual defaults in backends to workaround compiler exception

It's difficult to fix KT-22818 until the IR comes along, so we're
providing a workaround where one can disable the
ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS error and provide default values
in the actual function, to avoid exception from the backend.

 #KT-22818

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/CodegenUtil.kt

@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.resolve.calls.callUtil.getResolvedCall
 import org.jetbrains.kotlin.resolve.checkers.ExpectedActualDeclarationChecker
 import org.jetbrains.kotlin.resolve.multiplatform.ExpectedActualResolver
 import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.utils.DFS
 
 object CodegenUtil {
     @JvmStatic
@@ -200,16 +201,25 @@ object CodegenUtil {
         trace: DiagnosticSink?
     ): List<ValueParameterDescriptor> {
         if (descriptor.isActual) {
+            val actualParameters = descriptor.valueParameters
+            if (actualParameters.any { it.declaresOrInheritsDefaultValue() }) {
+                // This is incorrect code: actual function cannot have default values, they should be declared in the expected function.
+                // But until KT-22818 is fixed, we need to provide a workaround for the exception that happens on complex default values
+                // in the expected function. One may suppress the error then, and declare default values _both_ in expect and actual.
+                // With this code, we'll generate actual default values if they're present, and expected default values otherwise.
+                return actualParameters
+            }
+
             val expected = CodegenUtil.findExpectedFunctionForActual(descriptor)
             if (expected != null && expected.valueParameters.any(ValueParameterDescriptor::declaresDefaultValue)) {
                 val element = DescriptorToSourceUtils.descriptorToDeclaration(expected)
                 if (element == null) {
                     if (trace != null) {
                         val actualDeclaration = DescriptorToSourceUtils.descriptorToDeclaration(descriptor)
-                                ?: error("Not a source declaration: $descriptor")
+                            ?: error("Not a source declaration: $descriptor")
                         trace.report(Errors.EXPECTED_FUNCTION_SOURCE_WITH_DEFAULT_ARGUMENTS_NOT_FOUND.on(actualDeclaration))
                     }
-                    return descriptor.valueParameters
+                    return actualParameters
                 }
 
                 return expected.valueParameters
@@ -218,6 +228,16 @@ object CodegenUtil {
 
         return descriptor.valueParameters
     }
+
+    // This function is private here because no one is supposed to use it except for the hack above.
+    // Please use ValueParameterDescriptor.hasDefaultValue instead.
+    private fun ValueParameterDescriptor.declaresOrInheritsDefaultValue(): Boolean {
+        return DFS.ifAny(
+            listOf(this),
+            { current -> current.overriddenDescriptors.map(ValueParameterDescriptor::getOriginal) },
+            { it.declaresDefaultValue() }
+        )
+    }
 }
 
 fun DeclarationDescriptor.isTopLevelInPackage(name: String, packageName: String): Boolean {
@@ -226,4 +246,4 @@ fun DeclarationDescriptor.isTopLevelInPackage(name: String, packageName: String)
     val containingDeclaration = containingDeclaration as? PackageFragmentDescriptor ?: return false
     val packageFqName = containingDeclaration.fqName.asString()
     return packageName == packageFqName
-}
+}

compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt

@@ -0,0 +1,28 @@
+// !LANGUAGE: +MultiPlatformProjects
+// IGNORE_BACKEND: JVM_IR, JS_IR
+// FILE: common.kt
+
+public expect fun <T> Array<out T>.copyInto(
+    destination: Array<T>, destinationOffset: Int = 0, startIndex: Int = 0, endIndex: Int = size
+): Array<T>
+
+// FILE: platform.kt
+
+// This test should be updated once KT-22818 is fixed; default values are not allowed in the actual function
+@Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
+public actual fun <T> Array<out T>.copyInto(
+    destination: Array<T>, destinationOffset: Int = 42, startIndex: Int = 43, endIndex: Int = size + 44
+): Array<T> {
+    destination as Array<Int>
+    destination[0] = destinationOffset
+    destination[1] = startIndex
+    destination[2] = endIndex
+    return destination
+}
+
+fun box(): String {
+    val a = Array<Int>(3) { it }
+    val result = a.copyInto(a)
+    return if (result[0] == 42 && result[1] == 43 && result[2] == 47) "OK"
+           else "Fail: ${result[0]} ${result[1]} ${result[2]}"
+}

compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt

@@ -0,0 +1,30 @@
+// !LANGUAGE: +MultiPlatformProjects
+// IGNORE_BACKEND: JVM_IR, JS_IR
+// FILE: common.kt
+
+expect interface I {
+    fun test(source: String = "expect")
+}
+
+expect interface J : I
+
+// FILE: platform.kt
+
+actual interface I {
+    // This test should be updated once KT-22818 is fixed; default values are not allowed in the actual function
+    @Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
+    actual fun test(source: String = "actual")
+}
+
+actual interface J : I {
+    override fun test(source: String) {
+        if (source != "actual") throw AssertionError(source)
+    }
+}
+
+class K : J
+
+fun box(): String {
+    K().test()
+    return "OK"
+}

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

@@ -14455,6 +14455,16 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/annotations.kt");
             }
 
+            @TestMetadata("bothInExpectAndActual.kt")
+            public void testBothInExpectAndActual() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt");
+            }
+
+            @TestMetadata("bothInExpectAndActual2.kt")
+            public void testBothInExpectAndActual2() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt");
+            }
+
             @TestMetadata("constructor.kt")
             public void testConstructor() throws Exception {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/constructor.kt");

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

@@ -14465,6 +14465,16 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/annotations.kt");
             }
 
+            @TestMetadata("bothInExpectAndActual.kt")
+            public void testBothInExpectAndActual() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt");
+            }
+
+            @TestMetadata("bothInExpectAndActual2.kt")
+            public void testBothInExpectAndActual2() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt");
+            }
+
             @TestMetadata("constructor.kt")
             public void testConstructor() throws Exception {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/constructor.kt");

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

@@ -14460,6 +14460,16 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/annotations.kt");
             }
 
+            @TestMetadata("bothInExpectAndActual.kt")
+            public void testBothInExpectAndActual() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt");
+            }
+
+            @TestMetadata("bothInExpectAndActual2.kt")
+            public void testBothInExpectAndActual2() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt");
+            }
+
             @TestMetadata("constructor.kt")
             public void testConstructor() throws Exception {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/constructor.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/IrJsCodegenBoxTestGenerated.java

@@ -12640,6 +12640,16 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/multiplatform/defaultArguments"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JS_IR, true);
             }
 
+            @TestMetadata("bothInExpectAndActual.kt")
+            public void testBothInExpectAndActual() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt");
+            }
+
+            @TestMetadata("bothInExpectAndActual2.kt")
+            public void testBothInExpectAndActual2() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt");
+            }
+
             @TestMetadata("constructor.kt")
             public void testConstructor() throws Exception {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/constructor.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -13700,6 +13700,16 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
                 KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/multiplatform/defaultArguments"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JS, true);
             }
 
+            @TestMetadata("bothInExpectAndActual.kt")
+            public void testBothInExpectAndActual() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual.kt");
+            }
+
+            @TestMetadata("bothInExpectAndActual2.kt")
+            public void testBothInExpectAndActual2() throws Exception {
+                runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/bothInExpectAndActual2.kt");
+            }
+
             @TestMetadata("constructor.kt")
             public void testConstructor() throws Exception {
                 runTest("compiler/testData/codegen/box/multiplatform/defaultArguments/constructor.kt");