Auto merge of #85953 - inquisitivecrystal:weak-linkat-in-fs-hardlink, r=joshtriplett

Fix linker error

Currently, `fs::hard_link` determines whether platforms have `linkat` based on the OS, and uses `link` if they don't. However, this heuristic does not work well if a platform provides `linkat` on newer versions but not on older ones. On old MacOS, this currently causes a linking error.

This commit fixes `fs::hard_link` by telling it to use `weak!` on macOS. This means that, on  that operating system, we now check for `linkat` at runtime and use `link` if it is not available.

Fixes #80804.

`@rustbot` label T-libs-impl

1 files changed, 10 insertions, 3 deletions

diff --git a/library/std/src/sys/unix/weak.rs b/library/std/src/sys/unix/weak.rs
index 432fe4c33bc..cad8be6d289 100644
--- a/library/std/src/sys/unix/weak.rs
+++ b/library/std/src/sys/unix/weak.rs
@@ -26,8 +26,11 @@ use crate::marker;
 use crate::mem;
 use crate::sync::atomic::{self, AtomicUsize, Ordering};
 
-macro_rules! weak {
+// Temporary null documentation to work around #57569 until the fix is beta
+#[cfg_attr(bootstrap, doc = "")]
+pub(crate) macro weak {
     (fn $name:ident($($t:ty),*) -> $ret:ty) => (
+        #[allow(non_upper_case_globals)]
         static $name: crate::sys::weak::Weak<unsafe extern "C" fn($($t),*) -> $ret> =
             crate::sys::weak::Weak::new(concat!(stringify!($name), '\0'));
     )
@@ -100,8 +103,10 @@ unsafe fn fetch(name: &str) -> usize {
     libc::dlsym(libc::RTLD_DEFAULT, name.as_ptr()) as usize
 }
 
+// Temporary null documentation to work around #57569 until the fix is beta
+#[cfg_attr(bootstrap, doc = "")]
 #[cfg(not(any(target_os = "linux", target_os = "android")))]
-macro_rules! syscall {
+pub(crate) macro syscall {
     (fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
         unsafe fn $name($($arg_name: $t),*) -> $ret {
             use super::os;
@@ -118,10 +123,12 @@ macro_rules! syscall {
     )
 }
 
+#[cfg_attr(bootstrap, doc = "")]
 #[cfg(any(target_os = "linux", target_os = "android"))]
-macro_rules! syscall {
+pub(crate) macro syscall {
     (fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
         unsafe fn $name($($arg_name:$t),*) -> $ret {
+            use weak;
             // This looks like a hack, but concat_idents only accepts idents
             // (not paths).
             use libc::*;