Auto merge of #129341 - madsmtm:refactor-deployment-target, r=petrochenkov

Apple: Refactor deployment target version parsing

Refactor deployment target parsing to make it easier to do https://github.com/rust-lang/rust/pull/129342 (I wanted to make sure of all the places that `std::env::var` is called).

Specifically, my goal was to minimize the amount of target-specific configuration, so to that end I renamed the `opts` function that generates the `TargetOptions` to `base`, and made it return the LLVM target and `target_arch` too. In the future, I would like to move even more out of the target files and into `spec::apple`, as it makes it easier for me to maintain.

For example, this fixed a bug in `aarch64-apple-watchos`, which wasn't passing the deployment target as part of the LLVM triple. This (probably) fixes https://github.com/rust-lang/rust/issues/123582 and fixes https://github.com/rust-lang/rust/issues/107630.

We also now parse the patch version of deployment targets, allowing the user to specify e.g. `MACOSX_DEPLOYMENT_TARGET=10.12.6`.

Finally, this fixes the LLVM target name for visionOS, it should be `*-apple-xros` and not `*-apple-visionos`.

Since I have changed all the Apple targets here, I smoke-tested my changes by running the following:
```console
# Build each target
./x build library --target="aarch64-apple-darwin,aarch64-apple-ios,aarch64-apple-ios-macabi,aarch64-apple-ios-sim,aarch64-apple-tvos,aarch64-apple-tvos-sim,aarch64-apple-visionos,aarch64-apple-visionos-sim,aarch64-apple-watchos,aarch64-apple-watchos-sim,arm64_32-apple-watchos,arm64e-apple-ios,armv7k-apple-watchos,armv7s-apple-ios,i386-apple-ios,x86_64-apple-darwin,x86_64-apple-ios,x86_64-apple-ios-macabi,x86_64-apple-tvos,x86_64-apple-watchos-sim,x86_64h-apple-darwin"

# Test that we can still at least link basic projects
cargo new foobar && cd foobar && cargo +stage1 build --target=aarch64-apple-darwin --target=aarch64-apple-ios --target=aarch64-apple-ios-macabi --target=aarch64-apple-ios-sim --target=aarch64-apple-tvos --target=aarch64-apple-tvos-sim --target=aarch64-apple-visionos --target=aarch64-apple-visionos-sim --target=aarch64-apple-watchos --target=aarch64-apple-watchos-sim --target=arm64_32-apple-watchos --target=armv7s-apple-ios --target=i386-apple-ios --target=x86_64-apple-darwin --target=x86_64-apple-ios --target=x86_64-apple-ios-macabi --target=x86_64-apple-tvos --target=x86_64-apple-watchos-sim --target=x86_64h-apple-darwin
```

I couldn't build for the `arm64e-apple-darwin` target, the `armv7k-apple-watchos` and `arm64e-apple-ios` targets failed to link, and I know that the `i686-apple-darwin` target requires a bit of setup, but all of this is as it was before this PR.

r? thomcc

CC `@BlackHoleFox`

I would recommend using `rollup=never` when merging this, in case we need to bisect this later.

1 files changed, 24 insertions, 9 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 9b5a797ad51..0fd9d7fffe8 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -372,27 +372,42 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
     Some(file)
 }
 
-/// Since Xcode 15 Apple's LD requires object files to contain information about what they were
-/// built for (LC_BUILD_VERSION): the platform (macOS/watchOS etc), minimum OS version, and SDK
-/// version. This returns a `MachOBuildVersion` for the target.
+/// Mach-O files contain information about:
+/// - The platform/OS they were built for (macOS/watchOS/Mac Catalyst/iOS simulator etc).
+/// - The minimum OS version / deployment target.
+/// - The version of the SDK they were targetting.
+///
+/// In the past, this was accomplished using the LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS,
+/// LC_VERSION_MIN_TVOS or LC_VERSION_MIN_WATCHOS load commands, which each contain information
+/// about the deployment target and SDK version, and implicitly, by their presence, which OS they
+/// target. Simulator targets were determined if the architecture was x86_64, but there was e.g. a
+/// LC_VERSION_MIN_IPHONEOS present.
+///
+/// This is of course brittle and limited, so modern tooling emit the LC_BUILD_VERSION load
+/// command (which contains all three pieces of information in one) when the deployment target is
+/// high enough, or the target is something that wouldn't be encodable with the old load commands
+/// (such as Mac Catalyst, or Aarch64 iOS simulator).
+///
+/// Since Xcode 15, Apple's LD apparently requires object files to use this load command, so this
+/// returns the `MachOBuildVersion` for the target to do so.
 fn macho_object_build_version_for_target(target: &Target) -> object::write::MachOBuildVersion {
     /// The `object` crate demands "X.Y.Z encoded in nibbles as xxxx.yy.zz"
     /// e.g. minOS 14.0 = 0x000E0000, or SDK 16.2 = 0x00100200
-    fn pack_version((major, minor): (u32, u32)) -> u32 {
-        (major << 16) | (minor << 8)
+    fn pack_version((major, minor, patch): (u16, u8, u8)) -> u32 {
+        let (major, minor, patch) = (major as u32, minor as u32, patch as u32);
+        (major << 16) | (minor << 8) | patch
     }
 
     let platform =
         rustc_target::spec::current_apple_platform(target).expect("unknown Apple target OS");
-    let min_os = rustc_target::spec::current_apple_deployment_target(target)
-        .expect("unknown Apple target OS");
-    let sdk =
+    let min_os = rustc_target::spec::current_apple_deployment_target(target);
+    let (sdk_major, sdk_minor) =
         rustc_target::spec::current_apple_sdk_version(platform).expect("unknown Apple target OS");
 
     let mut build_version = object::write::MachOBuildVersion::default();
     build_version.platform = platform;
     build_version.minos = pack_version(min_os);
-    build_version.sdk = pack_version(sdk);
+    build_version.sdk = pack_version((sdk_major, sdk_minor, 0));
     build_version
 }