ObjCExport: enable unitSuspendFunctionObjCExport=proper by default

For Unit-returning suspend functions ObjCExport now generates
completion handlers without redundant `KotlinUnit*` result parameter.

So Swift (5.5+) can import these functions as Void-returning async
functions.

unitSuspendFunctionObjCExport=legacy binary option can be used to
enable the legacy behaviour. It will be removed in a future release.

^KT-49928 Fixed

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/KonanConfig.kt

@@ -314,7 +314,7 @@ class KonanConfig(val project: Project, val configuration: CompilerConfiguration
     }
 
     internal val unitSuspendFunctionObjCExport: UnitSuspendFunctionObjCExport
-        get() = configuration.get(BinaryOptions.unitSuspendFunctionObjCExport) ?: UnitSuspendFunctionObjCExport.LEGACY
+        get() = configuration.get(BinaryOptions.unitSuspendFunctionObjCExport) ?: UnitSuspendFunctionObjCExport.DEFAULT
 
     internal val testDumpFile: File? = configuration[KonanConfigKeys.TEST_DUMP_OUTPUT_PATH]?.let(::File)
 }

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/UnitSuspendFunctionObjCExport.kt

@@ -23,4 +23,9 @@ enum class UnitSuspendFunctionObjCExport {
      * async functions with `Void` return type
      */
     PROPER,
+    ;
+
+    companion object {
+        val DEFAULT = PROPER
+    }
 }

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/objcexport/ObjCExportNamer.kt

@@ -90,7 +90,7 @@ fun createNamer(
 ): ObjCExportNamer = ObjCExportNamerImpl(
         (exportedDependencies + moduleDescriptor).toSet(),
         moduleDescriptor.builtIns,
-        ObjCExportMapper(local = true, unitSuspendFunctionExport = UnitSuspendFunctionObjCExport.LEGACY),
+        ObjCExportMapper(local = true, unitSuspendFunctionExport = UnitSuspendFunctionObjCExport.DEFAULT),
         topLevelNamePrefix,
         local = true
 )

kotlin-native/backend.native/tests/build.gradle

@@ -5353,7 +5353,7 @@ if (isAppleTarget(project)) {
         framework(frameworkName) {
             sources = ['objcexport']
             library = libraryName
-            opts = ["-Xemit-lazy-objc-header=$lazyHeader", "-Xexport-kdoc", "-Xbundle-id=foo.bar", "-Xbinary=unitSuspendFunctionObjCExport=proper"]
+            opts = ["-Xemit-lazy-objc-header=$lazyHeader", "-Xexport-kdoc", "-Xbundle-id=foo.bar"]
         }
         swiftSources = ['objcexport']
         if (isNoopGC) {
@@ -5407,7 +5407,7 @@ if (isAppleTarget(project)) {
             sources = ['objcexport']
             artifact = frameworkArtifactName
             library = libraryName
-            opts = ["-Xemit-lazy-objc-header=$lazyHeader", "-Xno-objc-generics", "-Xbinary=unitSuspendFunctionObjCExport=proper"]
+            opts = ["-Xemit-lazy-objc-header=$lazyHeader", "-Xno-objc-generics"]
         }
         swiftSources = ['objcexport']
         swiftExtraOpts = [ '-D', 'NO_GENERICS' ]
@@ -5462,7 +5462,7 @@ if (isAppleTarget(project)) {
             sources = ['objcexport']
             artifact = frameworkArtifactName
             library = libraryName
-            opts = ["-Xemit-lazy-objc-header=$lazyHeader"]
+            opts = ["-Xemit-lazy-objc-header=$lazyHeader", "-Xbinary=unitSuspendFunctionObjCExport=legacy"]
         }
         swiftSources = ['objcexport']
         swiftExtraOpts = [ '-D', 'LEGACY_SUSPEND_UNIT_FUNCTION_EXPORT' ]
@@ -5497,7 +5497,6 @@ if (isAppleTarget(project)) {
             artifact = frameworkArtifactName
             library = libraryName
             isStatic = true
-            opts = ["-Xbinary=unitSuspendFunctionObjCExport=proper"]
         }
         swiftSources = ['objcexport']
         if (isNoopGC) {