KT-27524 Don't box (some) inline classes in suspend fun return

If an inline class is mapped to a reference type (or an array), it's Ok
to treat JVM view on a suspend function as returning a value of
corresponding inline class (although in reality it returns 'Any?'
because of COROUTINE_SUSPENDED).

compiler/backend/src/org/jetbrains/kotlin/codegen/Callable.kt

@@ -37,7 +37,7 @@ interface Callable {
 
     fun invokeMethodWithArguments(resolvedCall: ResolvedCall<*>, receiver: StackValue, codegen: ExpressionCodegen): StackValue {
         // it's important to use unsubstituted return type here to unbox value if it comes from type variable
-        return StackValue.functionCall(returnType, resolvedCall.resultingDescriptor.original.returnType) {
+        return StackValue.functionCall(returnType, returnKotlinType ?: resolvedCall.resultingDescriptor.original.returnType) {
             codegen.invokeMethodWithArguments(this, resolvedCall, receiver)
         }
     }

compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java

@@ -1648,7 +1648,7 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
             }
             else {
                 returnType = this.returnType;
-                returnKotlinType = this.context.getFunctionDescriptor().getReturnType();
+                returnKotlinType = typeMapper.getReturnValueType(this.context.getFunctionDescriptor());
             }
             StackValue valueToReturn = returnedExpression != null ? gen(returnedExpression) : StackValue.none();
 
@@ -1701,7 +1701,10 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
                             BindingContextUtils.getContainingFunctionSkipFunctionLiterals(descriptor, true).getFirst();
                     //FIRST_FUN_LABEL to prevent clashing with existing labels
                     return new NonLocalReturnInfo(
-                            new JvmKotlinType(typeMapper.mapReturnType(containingFunction), containingFunction.getReturnType()),
+                            new JvmKotlinType(
+                                    typeMapper.mapReturnType(containingFunction),
+                                    typeMapper.getReturnValueType(containingFunction)
+                            ),
                             FIRST_FUN_LABEL
                     );
                 } else {
@@ -1739,7 +1742,9 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
                 : returnType;
 
         KotlinType kotlinTypeForExpression =
-                isBlockedNamedFunction || isVoidCoroutineLambda ? null : context.getFunctionDescriptor().getReturnType();
+                isBlockedNamedFunction || isVoidCoroutineLambda
+                ? null
+                : typeMapper.getReturnValueType(context.getFunctionDescriptor());
 
         gen(expr, typeForExpression, kotlinTypeForExpression);
 

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

@@ -362,6 +362,19 @@ class KotlinTypeMapper @JvmOverloads constructor(
         }
     }
 
+    fun getReturnValueType(functionDescriptor: FunctionDescriptor): KotlinType =
+        getActualReturnTypeForSuspendFunctionWithInlineClassReturnTypeHack(functionDescriptor)
+            ?: functionDescriptor.returnType!!
+
+    private fun getActualReturnTypeForSuspendFunctionWithInlineClassReturnTypeHack(functionDescriptor: FunctionDescriptor): KotlinType? {
+        val originalSuspendFunctionForJvmView = functionDescriptor.unwrapInitialDescriptorForSuspendFunction()
+        if (originalSuspendFunctionForJvmView === functionDescriptor) return null
+        val originalReturnType = originalSuspendFunctionForJvmView.returnType!!
+        if (!originalReturnType.isInlineClassType()) return null
+        val jvmReturnType = mapType(originalReturnType)
+        return if (AsmUtil.isPrimitive(jvmReturnType)) null else originalReturnType
+    }
+
     @JvmOverloads
     fun mapToCallableMethod(
         descriptor: FunctionDescriptor,
@@ -431,7 +444,7 @@ class KotlinTypeMapper @JvmOverloads constructor(
                     invokeOpcode = INVOKESTATIC
                     val originalDescriptor = descriptor.original
                     signature = mapSignatureSkipGeneric(originalDescriptor, OwnerKind.DEFAULT_IMPLS)
-                    returnKotlinType = originalDescriptor.returnType
+                    returnKotlinType = getReturnValueType(originalDescriptor)
                     if (descriptor is AccessorForCallableDescriptor<*> && descriptor.calleeDescriptor.hasJvmDefaultAnnotation()) {
                         owner = mapClass(functionParent)
                         isInterfaceMember = true
@@ -482,7 +495,7 @@ class KotlinTypeMapper @JvmOverloads constructor(
                         skipGenericSignature = true,
                         hasSpecialBridge = false
                     )
-                returnKotlinType = functionToCall.returnType
+                returnKotlinType = getReturnValueType(functionToCall)
 
                 val receiver = if (currentIsInterface && !originalIsInterface || functionParent is FunctionClassDescriptor)
                     declarationOwner
@@ -495,7 +508,7 @@ class KotlinTypeMapper @JvmOverloads constructor(
         } else {
             val originalDescriptor = functionDescriptor.original
             signature = mapSignatureSkipGeneric(originalDescriptor)
-            returnKotlinType = originalDescriptor.returnType
+            returnKotlinType = getReturnValueType(originalDescriptor)
             owner = mapOwner(functionDescriptor)
             ownerForDefaultImpl = owner
             baseMethodDescriptor = functionDescriptor