Empty struct warning?

[anpete]

Native compiler is generating the following warning:

/var/folders/5_/ps5dhtf93d3gykbtr9stv7qh0000gn/T/konan_temp2849286529694188944/api.cpp:1033:15: warning: empty struct has size 0 in C, size 1 in C++ [-Wextern-c-compat]
              struct {
              ^

Can I ignore this? If so, how can I suppress it?

[olonho]

As clang suggests, use -Wno-extern-c-compat. This warning is harmless.

[anpete]

Thanks. I'm having trouble figuring out how to specify that using the Gradle multiplatform plugin. Any help would be much appreciated.

[artdfel]

Hello @anpete! Can you please share at which stage of the project build you're facing this warning?

[anpete]

The warning is produced when executing any of the link gradle tasks that are provided via the kotlin multiplatform plugin. The warnings started appearing after I made several types and global functions internal. Could it be related to kotlin files that only have internal declarations?

[artdfel]

Please try to add the flag to the linkerOpts property of your binary. Example of its usage one can find in this document.

[olonho]

compilerOpts, not linker one.

[anpete]

Assuming you mean freeCompilerArgs?

I tried this:

mingwX64("mingw") {
        binaries {
            sharedLib {
                baseName = "mylib"
                freeCompilerArgs = mutableListOf("-Wno-extern-c-compat")
            }
        }
    }

And got this:

e: Invalid argument: -Wno-extern-c-compat

[artdfel]

Hello again, @anpete, and sorry for such a long period of silence!
Finally, we managed to find the root cause of this warning. It has to be fixed in the compiler, so nothing can be done from your side.
Also, I got to mention that this issue should not cause any problems(except the fact that it is quietly annoying😅). So, please don't
worry about it, and wait for an update in this thread.

[anpete]

OK, thanks!

Feel free to close the issue when appropriate.

[vvlevchenko]

According to migrating issue tracking to YouTrack, closing this issue in favour of KT-42796 [Reverse C Interop] Package with no public methods generate empty struct in the header, leading to an error