Missing `Dart_InitializeApiDL` symbol in plugin using package:objective_c

[alevlako]

I wrote and tested my code in Swift, made a wrapper for it in Objective C, everything works up to this point. Now I need to call this code from Dart. I turned to the ffigen package and for several days I could not achieve a working result. Then I decided to check the simplest option - and I found that even base Swift example here does not work (
I have the macOs 13.7 installed.

I get the following error message when I try to run the example after all the preparation described in the readme (for default example pubspec.yaml):
swift_api_bindings.dart:26780:12: Error: Can't declare a member that conflicts with an inherited one.
bool get isProxy {
^^^^^^^
../../../objective_c/lib/src/objective_c_bindings_generated.dart:6785:8: Context: This is the inherited member.
bool isProxy() {
^^^^^^^
Or for dependencies: objective_c: ^3.0.0, ffigen: ^15.0.0:
swift_api_bindings.dart:25294:12: Error: Can't declare a member that conflicts with an inherited one.
bool get isProxy {
^^^^^^^
../../../../../../../.pub-cache/hosted/pub.dev/objective_c-3.0.0/lib/src/objective_c_bindings_generated.dart:6785:8: Context: This is the inherited member.
bool isProxy() {
^^^^^^^

[liamappelbe]

Looks like the swift example is hitting #1220

[liamappelbe]

@alevlako Do want to file a separate bug to discuss the issues you're having with your own Swift bindings? The first thing to check is whether you can see the APIs you expect in the generated ObjC header.

[alevlako]

@liamappelbe I see in generated swift_api.h following code:

SWIFT_CLASS("_TtC12swift_module10SwiftClass")
@interface SwiftClass : NSObject
- (NSString * _Nonnull)sayHello SWIFT_WARN_UNUSED_RESULT;
@property (nonatomic) NSInteger someField;
- (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
@end

I commented out getter isProxy in generated file swift_api_bindings.dart and was able to receive the error in this example that I get in my project:

Exception has occurred.
ArgumentError (Invalid argument(s): Couldn't resolve native function 'Dart_InitializeApiDL' in 'objective_c.framework/objective_c' : No asset with id 'objective_c.framework/objective_c' found. No available native assets. Attempted to fallback to process lookup. dlsym(RTLD_DEFAULT, Dart_InitializeApiDL): symbol not found.
)

The exception occurs here (in last line of the code, in generated file swift_api_bindings.dart ):

class SwiftClass extends objc.NSObject {
  SwiftClass._(ffi.Pointer<objc.ObjCObject> pointer,
      {bool retain = false, bool release = false})
      : super.castFromPointer(pointer, retain: retain, release: release);

I am using the actual versions of dependencies:
dependencies:
ffi: ^2.1.3
objective_c: ^3.0.0

[liamappelbe]

Ok, let's set aside the swift example for now (I know what the issue is there, and I'll fix that separately). Let's just focus on your project.

Couldn't resolve native function 'Dart_InitializeApiDL' isn't related to swift bindings specifically. It means that whatever dylibs are being loaded don't contain that symbol.

Can you tell me more about your project? Are you writing a flutter app or a dart command line tool? What does your project do? What are you using swift interop for?

From that error, my guess is you're writing a dart tool, not a flutter app. That's possible, but has some limitations (certain Apple APIs won't work in a pure dart tool, such as UI APIs).

[alevlako]

@liamappelbe thank you for your interest in my problem.

The ultimate goal of my project is to create a flutter plugin package for all desktop operating systems. The Windows part I finished whithin limits of pure dart package, using only WinAPI. For Mac and Linux I need work with ffi for access to native libs. I already realized that pure dart package will not enough for this purpose. In particular, in MacOS, my code accesses the Carbon library, or if I want to be more accurate its part HIToolbox/TextInputSources.h.

At this stage, I can call my swift library in the Flutter application, which runs from Xcode or which is launched in macOS after release build in VSCode. The application crashes when I launch code in debug mode in VSCode because of carbon call.
And I have not yet been able to include my library wtitten in swift into the flutter plugin, not into the application that should use this plugin.

[liamappelbe]

Ok, if you're writing an ObjC/Swift plugin, then this shouldn't be too hard. The missing Dart_InitializeApiDL symbol is supposed to come from the package:objective_c plugin. Are you including that as a dependency? If you have package:objective_c as a dep, it's supposed to "just work", but this is still a relatively new plugin, so there might be a bug there.

[liamappelbe]

The examples are fixed, so this bug is now tracking @alevlako's specific issue, where the missing symbol error is showing up in a flutter plugin.

@alevlako The next step to debug this is to make sure that your plugin depends on the package:objective_c plugin, then build your plugin, then find your plugin's dylib and use nm to list its symbols. I'm wondering if Dart_InitializeApiDL is missing from the plugin (which means the error is in the build), or if the symbol is there but not being loaded (which means the plugin dylib is not being loaded correctly at runtime). Something like nm path/to/plugin.dylib | grep Dart_InitializeApiDL should work.