Support C enums with forward declarations

Interop/Indexer/src/main/kotlin/org/jetbrains/kotlin/native/interop/indexer/Indexer.kt

@@ -240,7 +240,13 @@ internal class NativeIndexImpl(val library: NativeLibrary, val verbose: Boolean
 
     private fun getEnumDefAt(cursor: CValue<CXCursor>): EnumDefImpl {
         if (clang_isCursorDefinition(cursor) == 0) {
-            TODO("support enum forward declarations")
+            val definitionCursor = clang_getCursorDefinition(cursor)
+            if (clang_isCursorDefinition(definitionCursor) != 0) {
+                return getEnumDefAt(definitionCursor)
+            } else {
+                TODO("support enum forward declarations: " +
+                        clang_getTypeSpelling(clang_getCursorType(cursor)).convertAndDispose())
+            }
         }
 
         return enumRegistry.getOrPut(cursor) {

backend.native/tests/build.gradle

@@ -2838,8 +2838,8 @@ kotlinNativeInterop {
         defFile 'interop/basics/cunsupported.def'
     }
 
-    cstructs {
-        defFile 'interop/basics/cstructs.def'
+    ctypes {
+        defFile 'interop/basics/ctypes.def'
     }
 
     if (isMac()) {
@@ -2935,10 +2935,10 @@ task interop_unsupported(type: RunInteropKonanTest) {
     interop = 'cunsupported'
 }
 
-task interop_structs(type: RunInteropKonanTest) {
+task interop_types(type: RunInteropKonanTest) {
     disabled = (project.testTarget == 'wasm32') // No interop for wasm yet.
-    source = "interop/basics/structs.kt"
-    interop = 'cstructs'
+    source = "interop/basics/types.kt"
+    interop = 'ctypes'
 }
 
 task interop_echo_server(type: RunInteropKonanTest) {

backend.native/tests/interop/basics/ctypes.def

@@ -8,4 +8,9 @@ struct StructWithConstFields {
 struct StructWithConstFields getStructWithConstFields() {
     struct StructWithConstFields result = { 111, 222 };
     return result;
-}
+}
+
+enum ForwardDeclaredEnum;
+enum ForwardDeclaredEnum {
+    ZERO, ONE, TWO
+};

backend.native/tests/interop/basics/types.kt

@@ -1,10 +1,12 @@
 import kotlinx.cinterop.*
 import kotlin.test.*
-import cstructs.*
+import ctypes.*
 
 fun main() {
     getStructWithConstFields().useContents {
         assertEquals(111, x)
         assertEquals(222, y)
     }
+
+    assertEquals(1u, ForwardDeclaredEnum.ONE.value)
 }

backend.native/tests/interop/objc/smoke.h

@@ -61,3 +61,8 @@ int formatStringLength(NSString* format, ...);
 
 #define STRING_MACRO @"String macro"
 #define CFSTRING_MACRO CFSTR("CFString macro")
+
+typedef NS_ENUM(int32_t, ForwardDeclaredEnum);
+typedef NS_ENUM(int32_t, ForwardDeclaredEnum) {
+    ZERO, ONE, TWO,
+};

backend.native/tests/interop/objc/smoke.kt

@@ -19,6 +19,8 @@ fun run() {
     testConversions()
     testWeakRefs()
 
+    assertEquals(2, ForwardDeclaredEnum.TWO.value)
+
     println(
             getSupplier(
                     invoke1(42) { it * 2 }