Odd issue with include paths and wasm32-wasi target because .h file gets detected as C rather than C++

[devsnek]

I apologize for not having a minimal reproduction but I honestly have no idea what is going on here. I am having to add these lines to my build script to make it work:

https://github.com/devsnek/airbus-fbw-rs/blob/8866d48b156b8d58930332b2824a280f4bcfee9b/build.rs#L47-L50

Without those lines, I see the following output:

  --- stderr
  clang version 11.0.0
  Target: wasm32-unknown-wasi
  Thread model: posix
  InstalledDir:
  ignoring nonexistent directory "C:\MSFS SDK\/WASM/wasi-sysroot/include/wasm32-wasi/c++/v1"
  ignoring nonexistent directory "lib\clang\11.0.0\include"
  ignoring nonexistent directory "C:\MSFS SDK\/WASM/wasi-sysroot/include/wasm32-wasi"
  ignoring duplicate directory "C:\MSFS SDK\/WASM/wasi-sysroot/include"
  #include "..." search starts here:
  #include <...> search starts here:
   ./airbus-fbw-bench/src-model/src
   C:\Program Files\LLVM\lib\clang\11.0.0\include
   C:\MSFS SDK\/WASM/wasi-sysroot/include
   C:\MSFS SDK\/WASM/wasi-sysroot/include/c++/v1
  End of search list.
  C:\MSFS SDK\/WASM/wasi-sysroot/include/c++/v1\cstddef:44:15: fatal error: 'stddef.h' file not found
  C:\MSFS SDK\/WASM/wasi-sysroot/include/c++/v1\cstddef:44:15: fatal error: 'stddef.h' file not found, err: true
  thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ()', build.rs:58:14
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[kulp]

@devsnek, what about if you add .clang_arg("-xc++") instead ? I wonder if this is a C vs. C++ autodetection issue.

[devsnek]

@kulp that does seem to work.

[kulp]

@devsnek, regardless, you are not the first person to trip over this. There are some recent issues where this flag cleared up the problem too. If I find those issues I will link them here.

Basically, bindgen is not autodetecting language like you are expecting. If the header file you are trying to wrap is named .h instead of .hpp, that would explain it (ideally your issue report should show the invocation of bindgen, not just the error output).

[devsnek]

maybe bindgen could print out what language it thinks is being used so you know if you have to override it

[emilio]

Yeah, bindgen defaults to c for .h files. Getting some smarts here would be great if this trips people. Maybe just printing the language we're detecting on error messages would be a good improvement.