Always add LC_BUILD_VERSION for metadata object files

As of Xcode 15 Apple's linker has become a bit more strict about the
warnings it produces. One of those new warnings requires all valid
Mach-O object files in an archive to have a LC_BUILD_VERSION load
command:

```
ld: warning: no platform load command found in 'ARCHIVE[arm64][2106](lib.rmeta)', assuming: iOS-simulator
```

This was already being done for Mac Catalyst so this change expands this
logic to include it for all Apple platforms. I filed this behavior
change as FB12546320 and was told it was the new intentional behavior.

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -226,9 +226,7 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
 
     let mut file = write::Object::new(binary_format, architecture, endianness);
     if sess.target.is_like_osx {
-        if let Some(build_version) = macho_object_build_version_for_target(&sess.target) {
-            file.set_macho_build_version(build_version)
-        }
+        file.set_macho_build_version(macho_object_build_version_for_target(&sess.target))
     }
     let e_flags = match architecture {
         Architecture::Mips => {
@@ -334,31 +332,28 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
     Some(file)
 }
 
-/// Apple's LD, when linking for Mac Catalyst, 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` if necessary for the target.
-fn macho_object_build_version_for_target(
-    target: &Target,
-) -> Option<object::write::MachOBuildVersion> {
-    if !target.llvm_target.ends_with("-macabi") {
-        return None;
-    }
+/// 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.
+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)
     }
 
-    let platform = object::macho::PLATFORM_MACCATALYST;
-    let min_os = (14, 0);
-    let sdk = (16, 2);
+    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 =
+        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);
-    Some(build_version)
+    build_version
 }
 
 pub enum MetadataPosition {

compiler/rustc_driver_impl/src/lib.rs

@@ -858,11 +858,9 @@ fn print_crate_info(
                 use rustc_target::spec::current_apple_deployment_target;
 
                 if sess.target.is_like_osx {
-                    println_info!(
-                        "deployment_target={}",
-                        current_apple_deployment_target(&sess.target)
-                            .expect("unknown Apple target OS")
-                    )
+                    let (major, minor) = current_apple_deployment_target(&sess.target)
+                        .expect("unknown Apple target OS");
+                    println_info!("deployment_target={}", format!("{major}.{minor}"))
                 } else {
                     handler
                         .early_error("only Apple targets currently support deployment version info")

compiler/rustc_target/src/spec/apple_base.rs

@@ -179,20 +179,66 @@ pub fn opts(os: &'static str, arch: Arch) -> TargetOptions {
     }
 }
 
-pub fn deployment_target(target: &Target) -> Option<String> {
+pub fn sdk_version(platform: u32) -> Option<(u32, u32)> {
+    match platform {
+        object::macho::PLATFORM_MACOS => Some((13, 1)),
+        object::macho::PLATFORM_IOS
+        | object::macho::PLATFORM_IOSSIMULATOR
+        | object::macho::PLATFORM_TVOS
+        | object::macho::PLATFORM_TVOSSIMULATOR
+        | object::macho::PLATFORM_MACCATALYST => Some((16, 2)),
+        object::macho::PLATFORM_WATCHOS | object::macho::PLATFORM_WATCHOSSIMULATOR => Some((9, 1)),
+        _ => None,
+    }
+}
+
+pub fn platform(target: &Target) -> Option<u32> {
+    Some(match &*target.os {
+        "macos" => object::macho::PLATFORM_MACOS,
+        "ios" => {
+            if target.llvm_target.ends_with("-macabi") {
+                object::macho::PLATFORM_MACCATALYST
+            } else if target.llvm_target.ends_with("-simulator") {
+                object::macho::PLATFORM_IOSSIMULATOR
+            } else {
+                object::macho::PLATFORM_IOS
+            }
+        }
+        "watchos" => {
+            if target.llvm_target.ends_with("-simulator") {
+                object::macho::PLATFORM_WATCHOSSIMULATOR
+            } else {
+                object::macho::PLATFORM_WATCHOS
+            }
+        }
+        "tvos" => {
+            if target.llvm_target.ends_with("-simulator") {
+                object::macho::PLATFORM_TVOSSIMULATOR
+            } else {
+                object::macho::PLATFORM_TVOS
+            }
+        }
+        _ => return None,
+    })
+}
+
+pub fn deployment_target(target: &Target) -> Option<(u32, u32)> {
     let (major, minor) = match &*target.os {
         "macos" => {
             // This does not need to be specific. It just needs to handle x86 vs M1.
             let arch = if target.arch == "x86" || target.arch == "x86_64" { X86_64 } else { Arm64 };
             macos_deployment_target(arch)
         }
-        "ios" => ios_deployment_target(),
+        "ios" => match &*target.options.abi {
+            "macabi" => mac_catalyst_deployment_target(),
+            _ => ios_deployment_target(),
+        },
         "watchos" => watchos_deployment_target(),
         "tvos" => tvos_deployment_target(),
         _ => return None,
     };
 
-    Some(format!("{major}.{minor}"))
+    Some((major, minor))
 }
 
 fn from_set_deployment_target(var_name: &str) -> Option<(u32, u32)> {
@@ -274,6 +320,11 @@ fn ios_deployment_target() -> (u32, u32) {
     from_set_deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
 }
 
+fn mac_catalyst_deployment_target() -> (u32, u32) {
+    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
+    from_set_deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((14, 0))
+}
+
 pub fn ios_llvm_target(arch: Arch) -> String {
     // Modern iOS tooling extracts information about deployment target
     // from LC_BUILD_VERSION. This load command will only be emitted when

compiler/rustc_target/src/spec/mod.rs

@@ -61,6 +61,8 @@ mod aix_base;
 mod android_base;
 mod apple_base;
 pub use apple_base::deployment_target as current_apple_deployment_target;
+pub use apple_base::platform as current_apple_platform;
+pub use apple_base::sdk_version as current_apple_sdk_version;
 mod avr_gnu_base;
 pub use avr_gnu_base::ef_avr_arch;
 mod bpf_base;