Fix default/minimum deployment target for Aarch64 simulator targets

The minimum that `rustc` encoded did not match the version in Clang, and
that meant that that when linking, we ended up bumping the version.

Specifically, this sets the correct deployment target of the following
simulator and Mac Catalyst targets:
- `aarch64-apple-ios-sim` from 10.0 to 14.0
- `aarch64-apple-tvos-sim` from 10.0 to 14.0
- `aarch64-apple-watchos-sim` from 5.0 to 7.0
- `aarch64-apple-ios-macabi` from 13.1 to 14.0

I have chosen to not document the simulator target versions in the
platform support docs, as it is fundamentally uninteresting; the normal
targets (e.g. `aarch64-apple-ios`, `aarch64-apple-tvos`) still have the
same deployment target as before, and that's what developers should
actually target.

Author: madsmtm

compiler/rustc_target/src/spec/base/apple/mod.rs

@@ -323,12 +323,18 @@ fn deployment_target(os: &str, arch: Arch, abi: TargetAbi) -> (u16, u8, u8) {
     };
 
     // On certain targets it makes sense to raise the minimum OS version.
+    //
+    // This matches what LLVM does, see:
+    // <https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L1900-L1932>
     let min = match (os, arch, abi) {
-        // Use 11.0 on Aarch64 as that's the earliest version with M1 support.
         ("macos", Arch::Arm64 | Arch::Arm64e, _) => (11, 0, 0),
-        ("ios", Arch::Arm64e, _) => (14, 0, 0),
+        ("ios", Arch::Arm64 | Arch::Arm64e, TargetAbi::MacCatalyst) => (14, 0, 0),
+        ("ios", Arch::Arm64 | Arch::Arm64e, TargetAbi::Simulator) => (14, 0, 0),
+        ("ios", Arch::Arm64e, TargetAbi::Normal) => (14, 0, 0),
         // Mac Catalyst defaults to 13.1 in Clang.
         ("ios", _, TargetAbi::MacCatalyst) => (13, 1, 0),
+        ("tvos", Arch::Arm64 | Arch::Arm64e, TargetAbi::Simulator) => (14, 0, 0),
+        ("watchos", Arch::Arm64 | Arch::Arm64e, TargetAbi::Simulator) => (7, 0, 0),
         _ => os_min,
     };
 

src/doc/rustc/src/platform-support/apple-ios-macabi.md

@@ -24,7 +24,7 @@ environment variable.
 
 ### OS version
 
-The minimum supported version is iOS 13.1.
+The minimum supported version is iOS 13.1 on x86 and 14.0 on Aarch64.
 
 This can be raised per-binary by changing the deployment target. `rustc`
 respects the common environment variables used by Xcode to do so, in this

src/doc/rustc/src/platform-support/arm64e-apple-ios.md

@@ -2,7 +2,7 @@
 
 **Tier: 3**
 
-ARM64e iOS (12.0+)
+ARM64e iOS (14.0+)
 
 ## Target maintainers
 

tests/run-make/apple-deployment-target/rmake.rs

@@ -55,11 +55,8 @@ fn main() {
         rustc().env(env_var, example_version).run();
         minos("foo.o", example_version);
 
-        // FIXME(madsmtm): Doesn't work on Mac Catalyst and the simulator.
-        if !target().contains("macabi") && !target().contains("sim") {
-            rustc().env_remove(env_var).run();
-            minos("foo.o", default_version);
-        }
+        rustc().env_remove(env_var).run();
+        minos("foo.o", default_version);
     });
 
     // Test that version makes it to the linker when linking dylibs.
@@ -105,8 +102,18 @@ fn main() {
             rustc
         };
 
-        // FIXME(madsmtm): Doesn't work on watchOS for some reason?
-        if !target().contains("watchos") {
+        // FIXME(madsmtm): Xcode's version of Clang seems to require a minimum
+        // version of 9.0 on aarch64-apple-watchos for some reason? Which is
+        // odd, because the first Aarch64 watch was Apple Watch Series 4,
+        // which runs on as low as watchOS 5.0.
+        //
+        // You can see Clang's behaviour by running:
+        // ```
+        // echo "int main() { return 0; }" > main.c
+        // xcrun --sdk watchos clang --target=aarch64-apple-watchos main.c
+        // vtool -show a.out
+        // ```
+        if target() != "aarch64-apple-watchos" {
             rustc().env(env_var, example_version).run();
             minos("foo", example_version);
 
@@ -148,10 +155,7 @@ fn main() {
         rustc().env(env_var, higher_example_version).run();
         minos("foo.o", higher_example_version);
 
-        // FIXME(madsmtm): Doesn't work on Mac Catalyst and the simulator.
-        if !target().contains("macabi") && !target().contains("sim") {
-            rustc().env_remove(env_var).run();
-            minos("foo.o", default_version);
-        }
+        rustc().env_remove(env_var).run();
+        minos("foo.o", default_version);
     });
 }