Mac Catalyst: Read IPHONEOS_DEPLOYMENT_TARGET from environment variable to support Clang 13

[MikeChongCan]

Background

Clang 13 removed the x86_64-apple-ios13.0-macabi target, where 13.0 is hardcoded in cc-rs.

Proof:

➜  temp clang -target x86_64-apple-ios13.1-macabi i.c
➜  temp clang -target x86_64-apple-ios13.0-macabi i.c
clang-13: error: invalid version number in '-target x86_64-apple-ios13.0-macabi'
➜  temp clang --version
Homebrew clang version 13.0.1
Target: arm64-apple-darwin21.4.0
Thread model: posix
InstalledDir: /opt/homebrew/bin
➜  temp cat i.c

int main() {
	return 0;
}
➜  temp

This PR is to remove this hardcoded version and read it from IPHONEOS_DEPLOYMENT_TARGET.

Credits

@ehuss helped me found this reason: https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/Update.20Mac.20Catalyst.20support.20for.20Clang.2013/near/280745037

How to test

In this commit MikeChongCan/BLAKE3@f7bfd77, I changed cc-rs to my branch.

The build command and its output is like

➜  BLAKE3 git:(clang-13-mac-catalyst-demo) ✗ IPHONEOS_DEPLOYMENT_TARGET=13.1 cargo +nightly build -Z build-std --target x86_64-apple-ios-macabi
   Compiling compiler_builtins v0.1.71
   Compiling core v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/core)
   Compiling libc v0.2.121
   Compiling cc v1.0.69
   Compiling memchr v2.4.1
   Compiling std v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/std)
   Compiling version_check v0.9.4
   Compiling typenum v1.15.0
   Compiling cc v1.0.73 (https://github.com/imWildCat/cc-rs?branch=clang-13-mac-catalyst#310a43a5)
   Compiling generic-array v0.14.5
   Compiling blake3 v1.3.1 (/Volumes/SharedVol/rust-projects/BLAKE3)
   Compiling unwind v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/unwind)
   Compiling rustc-std-workspace-core v1.99.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling alloc v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/alloc)
   Compiling cfg-if v0.1.10
   Compiling adler v0.2.3
   Compiling rustc-demangle v0.1.21
   Compiling rustc-std-workspace-alloc v1.99.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/rustc-std-workspace-alloc)
   Compiling panic_unwind v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/panic_unwind)
   Compiling panic_abort v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/panic_abort)
   Compiling gimli v0.25.0
   Compiling std_detect v0.1.5 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/stdarch/crates/std_detect)
   Compiling object v0.26.2
   Compiling hashbrown v0.12.0
   Compiling miniz_oxide v0.4.0
   Compiling addr2line v0.16.0
   Compiling proc_macro v0.0.0 (/Users/wildcat/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/src/rust/library/proc_macro)
   Compiling subtle v2.4.1
   Compiling arrayref v0.3.6
   Compiling arrayvec v0.7.2
   Compiling constant_time_eq v0.1.5
   Compiling cfg-if v1.0.0
   Compiling block-buffer v0.10.2
   Compiling crypto-common v0.1.3
   Compiling digest v0.10.3
    Finished dev [unoptimized + debuginfo] target(s) in 12.88s

[MikeChongCan]

I'm not sure whether it is a good way. But as an iOS developer, I believe it makes sense. Because in Xcode, Mac Catalyst minimal version is highly related to minimal iOS version. For example, if I choose iOS 14.0, I can only pick macOS 11+ for this situation:

[dot-asm]

This is one of the things I'm suggesting to address differently in #664.

[thomcc]

So we no longer hardcode this as of #727. But I also think rustc itself is probably broken WRT how it handles catalyst, and would like to figure out the right fix there before doing too much in cc.

[MikeChongCan]

@thomcc sure, thanks for the update!