[ObjCExport] Initial implementation of function type translation

^KT-65167

native/objcexport-header-generator/impl/analysis-api/src/org/jetbrains/kotlin/objcexport/analysisApiUtils/getMethodBridge.kt

@@ -111,7 +111,7 @@ private fun bridgeFunctionType(type: KtType): TypeBridge {
 
     if (type is KtFunctionalType) {
         numberOfParameters = type.parameterTypes.size
-        returnType = type.parameterTypes.last()
+        returnType = type.returnType
     } else {
         numberOfParameters = 0
         returnType = type

native/objcexport-header-generator/impl/analysis-api/src/org/jetbrains/kotlin/objcexport/translateToObjCFunctionType.kt

@@ -1,11 +1,18 @@
-@file:Suppress("UNUSED_PARAMETER")
-
 package org.jetbrains.kotlin.objcexport
 
+import org.jetbrains.kotlin.analysis.api.KtAnalysisSession
+import org.jetbrains.kotlin.analysis.api.types.KtFunctionalType
 import org.jetbrains.kotlin.analysis.api.types.KtType
-import org.jetbrains.kotlin.backend.konan.objcexport.BlockPointerBridge
-import org.jetbrains.kotlin.backend.konan.objcexport.ObjCReferenceType
+import org.jetbrains.kotlin.backend.konan.objcexport.*
 
+context(KtAnalysisSession, KtObjCExportSession)
 internal fun KtType.translateToObjCFunctionType(typeBridge: BlockPointerBridge): ObjCReferenceType {
-    TODO()
+    if (this !is KtFunctionalType) return ObjCIdType
+
+    return ObjCBlockPointerType(
+        returnType = if (typeBridge.returnsVoid) ObjCVoidType else returnType.translateToObjCReferenceType(),
+        parameterTypes = listOfNotNull(this.receiverType).plus(this.parameterTypes).map { parameterType ->
+            parameterType.translateToObjCReferenceType()
+        }
+    )
 }

native/objcexport-header-generator/test/org/jetbrains/kotlin/backend/konan/tests/ObjCExportTypeTranslationTest.kt

@@ -69,6 +69,29 @@ class ObjCExportTypeTranslationTest(
         assertEquals("A *, B * _Nullable -> C * _Nullable", header.renderTypesOfSymbol("foo"))
     }
 
+    @Test
+    fun `test - Unit as return type`() {
+        val header = header(
+            """
+            fun foo() = Unit
+            """.trimIndent()
+        )
+
+        assertEquals(" -> void", header.renderTypesOfSymbol("foo"))
+    }
+
+    @Test
+    fun `test - Unit as parameter type`() {
+        val header = header(
+            """
+            fun foo(unit: Unit) = Unit
+            """.trimIndent()
+        )
+
+        assertEquals("Unit * -> void", header.renderTypesOfSymbol("foo"))
+    }
+
+
     @Test
     fun `test - hiddenTypes - Any - are exposed as id`() {
         val header = header("""fun foo(): Any""")