JVM_IR: KT-40293 Box return type for DefaultImpls methods if required

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt

@@ -43,6 +43,7 @@ class JvmCachedDeclarations(
     private val defaultImplsMethods = HashMap<IrSimpleFunction, IrSimpleFunction>()
     private val defaultImplsClasses = HashMap<IrClass, IrClass>()
     private val defaultImplsRedirections = HashMap<IrSimpleFunction, IrSimpleFunction>()
+    private val defaultImplsOriginalMethods = HashMap<IrSimpleFunction, IrSimpleFunction>()
 
     fun getFieldForEnumEntry(enumEntry: IrEnumEntry): IrField =
         singletonFieldDeclarations.getOrPut(enumEntry) {
@@ -176,10 +177,15 @@ class JvmCachedDeclarations(
                         it.annotations += irCall(this@JvmCachedDeclarations.context.ir.symbols.javaLangDeprecatedConstructor)
                     }
                 }
+
+                defaultImplsOriginalMethods[it] = interfaceFun
             }
         }
     }
 
+    fun getOriginalFunctionForDefaultImpl(defaultImplFun: IrSimpleFunction) =
+        defaultImplsOriginalMethods[defaultImplFun]
+
     fun getDefaultImplsClass(interfaceClass: IrClass): IrClass =
         defaultImplsClasses.getOrPut(interfaceClass) {
             context.irFactory.buildClass {

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/MethodSignatureMapper.kt

@@ -171,10 +171,20 @@ class MethodSignatureMapper(private val context: JvmBackendContext) {
     private fun hasVoidReturnType(function: IrFunction): Boolean =
         function is IrConstructor || (function.returnType.isUnit() && !function.isGetter)
 
-    // Copied from KotlinTypeMapper.forceBoxedReturnType.
-    private fun forceBoxedReturnType(function: IrFunction): Boolean = isBoxMethodForInlineClass(function) ||
-            function is IrSimpleFunction && function.returnType.isPrimitiveType() &&
-            function.allOverridden().any { !it.returnType.isPrimitiveType() }
+    // See also: KotlinTypeMapper.forceBoxedReturnType
+    private fun forceBoxedReturnType(function: IrFunction): Boolean =
+        isBoxMethodForInlineClass(function) || forceFoxedReturnTypeOnOverride(function) || forceBoxedReturnTypeOnDefaultImplFun(function)
+
+    private fun forceFoxedReturnTypeOnOverride(function: IrFunction) =
+        function is IrSimpleFunction &&
+                function.returnType.isPrimitiveType() &&
+                function.allOverridden().any { !it.returnType.isPrimitiveType() }
+
+    private fun forceBoxedReturnTypeOnDefaultImplFun(function: IrFunction): Boolean {
+        if (function !is IrSimpleFunction) return false
+        val originalFun = context.cachedDeclarations.getOriginalFunctionForDefaultImpl(function) ?: return false
+        return forceFoxedReturnTypeOnOverride(originalFun)
+    }
 
     private fun isBoxMethodForInlineClass(function: IrFunction): Boolean =
         function.parent.let { it is IrClass && it.isInline } &&

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/InterfaceLowering.kt

@@ -64,13 +64,13 @@ internal class InterfaceLowering(val context: JvmBackendContext) : IrElementTran
         val jvmDefaultMode = context.state.jvmDefaultMode
         val isCompatibilityMode = jvmDefaultMode.isCompatibility && !irClass.hasJvmDefaultNoCompatibilityAnnotation()
         // There are 6 cases for functions on interfaces:
-        loop@ for (function in irClass.functions) {
+        for (function in irClass.functions) {
             when {
                 /**
                  * 1) They are plain abstract interface functions, in which case we leave them:
                  */
                 function.modality == Modality.ABSTRACT ->
-                    continue@loop
+                    continue
 
                 /**
                  * 2) They inherit a default implementation from an interface this interface extends:
@@ -99,13 +99,13 @@ internal class InterfaceLowering(val context: JvmBackendContext) : IrElementTran
                     // (KT-36188) where there could be multiple implementations. (resolveFakeOverride() only returns the implementation if
                     // there's only one.)
                     if (function.name.asString().endsWith("\$default")) {
-                        continue@loop
+                        continue
                     }
                     val implementation = function.resolveFakeOverride() ?: error("No single implementation found for: ${function.render()}")
 
                     when {
                         Visibilities.isPrivate(implementation.visibility) || implementation.isMethodOfAny() ->
-                            continue@loop
+                            continue
                         !function.isDefinitelyNotDefaultImplsMethod(jvmDefaultMode, implementation) -> {
                             val defaultImpl = createDefaultImpl(function)
                             val superImpl = firstSuperMethodFromKotlin(function, implementation)

compiler/testData/codegen/bytecodeListing/jvm8/defaults/allCompatibility/specialization/primitiveAndAny.kt

@@ -1,7 +1,6 @@
 // !JVM_DEFAULT_MODE: all-compatibility
 // JVM_TARGET: 1.8
 // WITH_RUNTIME
-// IGNORE_BACKEND: JVM_IR
 
 interface Base {
     fun test(): Int? = 0

compiler/testData/codegen/bytecodeListing/jvm8/defaults/allCompatibility/specialization/primitiveAndNullable.kt

@@ -1,7 +1,6 @@
 // !JVM_DEFAULT_MODE: all-compatibility
 // JVM_TARGET: 1.8
 // WITH_RUNTIME
-// IGNORE_BACKEND: JVM_IR
 interface Base {
     fun test(): Int? = 0
 }