crosscompiling macos -> ios + xcodebuild + build-script problem

[Dushistov]

I call cargo build from my XCode project and build project for iOS.
One of my crates depend on bindgen, which depend on clang-sys,
which depend on libloading.

And build failed, with such error:

cargo:warning=In file included from src/os/unix/global_static.c:1:
cargo:warning=In file included from /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.5.sdk/usr/include/pthread.h:60:
cargo:warning=In file included from /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.5.sdk/usr/include/time.h:69:
cargo:warning=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.5.sdk/usr/include/sys/_types/_clock_t.h:31:9: error: unknown type name '__darwin_clock_t'
cargo:warning=typedef __darwin_clock_t clock_t;

libloading is part of build-script, so it should not be compiled for iOS,
it should be compiled for macOS, but for some reason it compiled for iOS instead of macOS.

Interesting thing that if I run cargo build --target=aarch64-apple-ios manually all works fine.

After analysing what environment variable set xcodebuild I thing culprit is

SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.5.sdk

because of with it

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "-m64" "-Wall" "-Wextra" "-o" "/tmp/global_static.o" "-c" /Users/evgeniy/.cargo/registry/src/github.com-1ecc6299db9ec823/libloading-0.5.2/src/os/unix/global_static.c

report the same problem, and if I change it into

export SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk

all works fine if I call cc manually.

[alexcrichton]

Yes this is where build processes using env vars aren't really always the best equipped for cross compilation. I'm not really sure what this crate could do, since it can't blindly remove SDKROOT from the environment...

[Dushistov]

I suppose it should detect target == host == macos and then if SDKROOT contains ios
set SDKROOT=macos , but I am not sure how to find proper content of SDKROOT for macos.

[alexcrichton]

Now that you mention it I recall that rustc does something similar, and that seems reasonable to add here too

[MichaelHills]

Is this the same as rust-lang/cargo#7283 ?

[Dushistov]

@MichaelHills

It is roughly the same. Problem with include search, not linking problem. In solution I set environment variable to right value, instead of removing variable etc. But it is roughly the same problem: problem of building build script if the whole build is run via xcodebuild