Add deployment-target --print flag for Apple targets

compiler/rustc_driver_impl/src/lib.rs

@@ -745,6 +745,22 @@ fn print_crate_info(
                     }
                 }
             }
+            DeploymentTarget => {
+                use rustc_target::spec::current_apple_deployment_target;
+
+                if sess.target.is_like_osx {
+                    safe_println!(
+                        "deployment_target={}",
+                        current_apple_deployment_target(&sess.target)
+                            .expect("unknown Apple target OS")
+                    )
+                } else {
+                    early_error(
+                        ErrorOutputType::default(),
+                        "only Apple targets currently support deployment version info",
+                    )
+                }
+            }
         }
     }
     Compilation::Stop

compiler/rustc_session/src/config.rs

@@ -587,6 +587,7 @@ pub enum PrintRequest {
     StackProtectorStrategies,
     LinkArgs,
     SplitDebuginfo,
+    DeploymentTarget,
 }
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
@@ -1452,7 +1453,7 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
             "[crate-name|file-names|sysroot|target-libdir|cfg|calling-conventions|\
              target-list|target-cpus|target-features|relocation-models|code-models|\
              tls-models|target-spec-json|all-target-specs-json|native-static-libs|\
-             stack-protector-strategies|link-args]",
+             stack-protector-strategies|link-args|deployment-target]",
         ),
         opt::flagmulti_s("g", "", "Equivalent to -C debuginfo=2"),
         opt::flagmulti_s("O", "", "Equivalent to -C opt-level=2"),
@@ -1902,6 +1903,7 @@ fn collect_print_requests(
         ("all-target-specs-json", PrintRequest::AllTargetSpecs),
         ("link-args", PrintRequest::LinkArgs),
         ("split-debuginfo", PrintRequest::SplitDebuginfo),
+        ("deployment-target", PrintRequest::DeploymentTarget),
     ];
 
     prints.extend(matches.opt_strs("print").into_iter().map(|req| {

compiler/rustc_target/src/spec/apple_base.rs

@@ -1,7 +1,7 @@
 use std::{borrow::Cow, env};
 
 use crate::spec::{cvs, Cc, DebuginfoKind, FramePointer, LinkArgs};
-use crate::spec::{LinkerFlavor, Lld, SplitDebuginfo, StaticCow, TargetOptions};
+use crate::spec::{LinkerFlavor, Lld, SplitDebuginfo, StaticCow, Target, TargetOptions};
 
 #[cfg(test)]
 #[path = "apple/tests.rs"]
@@ -179,12 +179,28 @@ pub fn opts(os: &'static str, arch: Arch) -> TargetOptions {
     }
 }
 
-fn deployment_target(var_name: &str) -> Option<(u32, u32)> {
-    let deployment_target = env::var(var_name).ok();
-    deployment_target
-        .as_ref()
-        .and_then(|s| s.split_once('.'))
-        .and_then(|(a, b)| a.parse::<u32>().and_then(|a| b.parse::<u32>().map(|b| (a, b))).ok())
+pub fn deployment_target(target: &Target) -> Option<String> {
+    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(),
+        "watchos" => watchos_deployment_target(),
+        "tvos" => tvos_deployment_target(),
+        _ => return None,
+    };
+
+    Some(format!("{major}.{minor}"))
+}
+
+fn from_set_deployment_target(var_name: &str) -> Option<(u32, u32)> {
+    let deployment_target = env::var(var_name).ok()?;
+    let (unparsed_major, unparsed_minor) = deployment_target.split_once('.')?;
+    let (major, minor) = (unparsed_major.parse().ok()?, unparsed_minor.parse().ok()?);
+
+    Some((major, minor))
 }
 
 fn macos_default_deployment_target(arch: Arch) -> (u32, u32) {
@@ -198,7 +214,8 @@ fn macos_default_deployment_target(arch: Arch) -> (u32, u32) {
 }
 
 fn macos_deployment_target(arch: Arch) -> (u32, u32) {
-    deployment_target("MACOSX_DEPLOYMENT_TARGET")
+    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
+    from_set_deployment_target("MACOSX_DEPLOYMENT_TARGET")
         .unwrap_or_else(|| macos_default_deployment_target(arch))
 }
 
@@ -247,7 +264,8 @@ fn link_env_remove(arch: Arch, os: &'static str) -> StaticCow<[StaticCow<str>]>
 }
 
 fn ios_deployment_target() -> (u32, u32) {
-    deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
+    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
+    from_set_deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
 }
 
 pub fn ios_llvm_target(arch: Arch) -> String {
@@ -272,7 +290,8 @@ pub fn ios_sim_llvm_target(arch: Arch) -> String {
 }
 
 fn tvos_deployment_target() -> (u32, u32) {
-    deployment_target("TVOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
+    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
+    from_set_deployment_target("TVOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
 }
 
 fn tvos_lld_platform_version() -> String {
@@ -281,7 +300,8 @@ fn tvos_lld_platform_version() -> String {
 }
 
 fn watchos_deployment_target() -> (u32, u32) {
-    deployment_target("WATCHOS_DEPLOYMENT_TARGET").unwrap_or((5, 0))
+    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
+    from_set_deployment_target("WATCHOS_DEPLOYMENT_TARGET").unwrap_or((5, 0))
 }
 
 fn watchos_lld_platform_version() -> String {

compiler/rustc_target/src/spec/mod.rs

@@ -60,6 +60,7 @@ pub mod crt_objects;
 mod aix_base;
 mod android_base;
 mod apple_base;
+pub use apple_base::deployment_target as current_apple_deployment_target;
 mod avr_gnu_base;
 mod bpf_base;
 mod dragonfly_base;

src/doc/rustc/src/command-line-arguments.md

@@ -248,8 +248,14 @@ The valid types of print values are:
   exact format of this debugging output is not a stable guarantee, other than
   that it will include the linker executable and the text of each command-line
   argument passed to the linker.
+- `deployment-target` - The currently selected [deployment target] (or minimum OS version)
+  for the selected Apple platform target. This value can be used or passed along to other
+  components alongside a Rust build that need this information, such as C compilers.
+  This returns rustc's minimum supported deployment target if no `*_DEPLOYMENT_TARGET` variable
+  is present in the environment, or otherwise returns the variable's parsed value.
 
 [conditional compilation]: ../reference/conditional-compilation.html
+[deployment target]: https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/cross_development/Configuring/configuring.html
 
 <a id="option-g-debug"></a>
 ## `-g`: include debug information

src/tools/tidy/src/ui_tests.rs

@@ -10,7 +10,7 @@ use std::path::{Path, PathBuf};
 const ENTRY_LIMIT: usize = 900;
 // FIXME: The following limits should be reduced eventually.
 const ISSUES_ENTRY_LIMIT: usize = 1953;
-const ROOT_ENTRY_LIMIT: usize = 894;
+const ROOT_ENTRY_LIMIT: usize = 895;
 
 fn check_entries(tests_path: &Path, bad: &mut bool) {
     let mut directories: HashMap<PathBuf, usize> = HashMap::new();

tests/run-make/valid-print-requests/valid-print-requests.stderr

@@ -1,2 +1,2 @@
-error: unknown print request `uwu`. Valid print requests are: `crate-name`, `file-names`, `sysroot`, `target-libdir`, `cfg`, `calling-conventions`, `target-list`, `target-cpus`, `target-features`, `relocation-models`, `code-models`, `tls-models`, `native-static-libs`, `stack-protector-strategies`, `target-spec-json`, `all-target-specs-json`, `link-args`, `split-debuginfo`
+error: unknown print request `uwu`. Valid print requests are: `crate-name`, `file-names`, `sysroot`, `target-libdir`, `cfg`, `calling-conventions`, `target-list`, `target-cpus`, `target-features`, `relocation-models`, `code-models`, `tls-models`, `native-static-libs`, `stack-protector-strategies`, `target-spec-json`, `all-target-specs-json`, `link-args`, `split-debuginfo`, `deployment-target`
 

tests/ui/deployment-target/invalid-target.rs

@@ -0,0 +1,4 @@
+// compile-flags: --target x86_64-unknown-linux-gnu --print deployment-target
+// needs-llvm-components: x86
+
+fn main() {}

tests/ui/deployment-target/invalid-target.stderr

@@ -0,0 +1,2 @@
+error: only Apple targets currently support deployment version info
+

tests/ui/deployment-target/macos-target.rs

@@ -0,0 +1,6 @@
+// only-macos
+// compile-flags: --print deployment-target
+// normalize-stdout-test: "\d+\.0" -> "$$CURRENT_MAJOR_VERSION.0"
+// check-pass
+
+fn main() {}

tests/ui/deployment-target/macos-target.stdout

@@ -0,0 +1 @@
+deployment_target=$CURRENT_MAJOR_VERSION.0