Is there a way to add additional `external expect fun` defin

Question

Is there a way to add additional `external expect fun` definitions to a pre defined ObjC interop I m using an ObjC cocoapods library and need to call a function that s not part of its public API for testing I know the function signature from its source code Basically I just need a way to ObjC message the function in Kotlin Or something akin to Java reflection to access it

Rick Clephas · Answer

I am not sure what you mean by pre defined ObjC interop but if you have any control over the used ` def` file you could add custom declarations <https kotlinlang org docs native c interop html add custom declarations>

Jeff Lockhart · Answer

By pre defined I mean that the cocoapods plugin handles generating the interop for the ObjC library The only ` def` file in the project is build cocoapods defs LibName def And the contents is ```language = Objective C modules = LibName``` I m not aware of a way to modify this since the cocoapods plugin handles generating the interop Is it possible to define another ` def` file for the same library

Rick Clephas · Answer

If I am not mistaken you can t use two cinterop files for the same library Though I think you should be able to modify the ` def` file and or use a custom ` def` file The cinterops can be created accessed in the `build gradle kts` file <https github com rickclephas NSErrorKt blob 17f92767016c9401cff6f3fc371c627cc41e693b nserror kt build gradle kts L44> Haven t looked at the source of the cocoapods plugin but I assume they are using the same feature In that case your cocoapods library should have a cinterop task

Jeff Lockhart · Answer

I did discover a way to define the most important method I need to access using the ` ObjCMethod` annotation ``` ObjCMethod selector = methodName encoding = 16 0 8 private external fun ObjCClass methodName Boolean``` I mostly stumbled upon this solution with trial and error I can t find its usage documented anywhere The `encoding` parameter is the hard part I m assuming I can find this somewhere from the ObjC compiler output But ` 16 0 8` seems to be valid for methods that have no parameters and works at least for the `Boolean` return type of the method I needed I based this off <https youtrack jetbrains com issue KT 39801 KotlinNative Swift Interop mystery import|this code snippet> and it just happened to work when I tried in my own code I ll have to look more into how best to get an ObjC method s encoding

Rick Clephas · Answer

Nice Didn t know about that

Rick Clephas · Answer

Just checked the cocoapods plugin source and we can actually modify the generated ` def` file ```tasks named lt org jetbrains kotlin gradle tasks DefFileTask gt generateDef$ pod moduleName doLast outputFile appendText static inline int getErrno return errno trimIndent ```

Jeff Lockhart · Answer

Awesome Do you know how a method as the one above would be defined describes a usage of implementing a method or macro in C But I really just need to describe an existing ObjC method signature as a header file would Since the class is already defined elsewhere in its own header maybe I d need to

Rick Clephas · Answer

I think you need to define a class extension instead Since you just need to expose an already existing method that s part of the original implementation

Jeff Lockhart · Answer

I ve been testing this out appending to the cocoapods def file I m able to see my additions appended in the generated def file I m also getting errors output when the cinterop task runs if something s undefined syntax error etc But once I resolve any errors and the task completes successfully I m not actually seeing any of my cinterop definitions accessible in Kotlin

Rick Clephas · Answer

Hmm is that also the case with a simple static function that e g returns a fixed integer or something

Jeff Lockhart · Answer

Yeah I just tested with this almost identical to the example ```static inline int doesThisWork return 1 ``` I can t find a reference to the function in Kotlin

Jeff Lockhart · Answer

Are you able to successfully reference the function doing this in your own code

Rick Clephas · Answer

I haven t tried this specific case yet Though I have been able to reference a function when manually creating cinterop tasks But I can do some testing tomorrow slightly smiling face

Rick Clephas · Answer

Did some testing and the good news is that it is indeed possible to expose the non public API To verify this I tried to expose the `firebaseUserAgent` property from `FIRApp` With the following ` def` file ```language = Objective C headers = FirebaseCore FIRApp h headerFilter = FirebaseCore interface FIRApp property class readonly nullable NSString firebaseUserAgent end``` I can print the user agent in Kotlin ```import cocoapods FirebaseCore FIRApp import cocoapods FirebaseCore firebaseUserAgent println FIRApp firebaseUserAgent ``` However the CocoaPods plugin generates the following ` def` file ```language = Objective C modules = FirebaseCore``` When `modules` is specified instead of `headers` and `headerFilter` the doesn t include the `mainFile` that contains our custom declarations < svyatoslav scherbina> any specific reason why the custom declarations aren t included when `modules` is used

svyatoslav.scherbina · Answer

gt I did discover a way to define the most important method I need to access using the ` ObjCMethod` annotation Please note that this annotation is not intended to be used manually and provides no compatibility guarantees Also the encoding is platform specific gt < svyatoslav scherbina> any specific reason why the custom declarations aren t included when `modules` is used Likely a bug As a workaround one can patch the generated ` def` file to use `headers =` and `headerFilter =` instead of `modules =`

Jeff Lockhart · Answer

Thanks for the clarification Should I create a YouTrack issue to report this bug

svyatoslav.scherbina · Answer

That would be helpful thank you

Jeff Lockhart · Answer

Here s the < Rick Clephas> thank you for all your help delving into this

Rick Clephas · Answer

NP I guess it should be an easy fix just adding `mainFile` to the list of headers but I am not sure how to cover that with tests slightly smiling face

svyatoslav.scherbina · Answer

Creating an interop test like <https github com JetBrains kotlin commit ea7160947ad541c35dbad90174b972fe9e16d29d|this> should be enough But instead of passing a path to header in `createInterop` an include path should be specified

Rick Clephas · Answer

FYI the PR with the fix <https github com JetBrains kotlin pull 4894>