Reduce monomorphisation bloat in small_c_string

library/std/src/sys/pal/common/small_c_string.rs

@@ -15,22 +15,28 @@ const NUL_ERR: io::Error =
     io::const_io_error!(io::ErrorKind::InvalidInput, "file name contained an unexpected NUL byte");
 
 #[inline]
-pub fn run_path_with_cstr<T, F>(path: &Path, f: F) -> io::Result<T>
-where
-    F: FnOnce(&CStr) -> io::Result<T>,
-{
+pub fn run_path_with_cstr<T>(path: &Path, f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
     run_with_cstr(path.as_os_str().as_encoded_bytes(), f)
 }
 
 #[inline]
-pub fn run_with_cstr<T, F>(bytes: &[u8], f: F) -> io::Result<T>
-where
-    F: FnOnce(&CStr) -> io::Result<T>,
-{
+pub fn run_with_cstr<T>(bytes: &[u8], f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
+    // Dispatch and dyn erase the closure type to prevent mono bloat.
+    // See https://github.com/rust-lang/rust/pull/121101.
     if bytes.len() >= MAX_STACK_ALLOCATION {
-        return run_with_cstr_allocating(bytes, f);
+        run_with_cstr_allocating(bytes, f)
+    } else {
+        unsafe { run_with_cstr_stack(bytes, f) }
     }
+}
 
+/// # Safety
+///
+/// `bytes` must have a length less than `MAX_STACK_ALLOCATION`.
+unsafe fn run_with_cstr_stack<T>(
+    bytes: &[u8],
+    f: &dyn Fn(&CStr) -> io::Result<T>,
+) -> io::Result<T> {
     let mut buf = MaybeUninit::<[u8; MAX_STACK_ALLOCATION]>::uninit();
     let buf_ptr = buf.as_mut_ptr() as *mut u8;
 
@@ -47,10 +53,7 @@ where
 
 #[cold]
 #[inline(never)]
-fn run_with_cstr_allocating<T, F>(bytes: &[u8], f: F) -> io::Result<T>
-where
-    F: FnOnce(&CStr) -> io::Result<T>,
-{
+fn run_with_cstr_allocating<T>(bytes: &[u8], f: &dyn Fn(&CStr) -> io::Result<T>) -> io::Result<T> {
     match CString::new(bytes) {
         Ok(s) => f(&s),
         Err(_) => Err(NUL_ERR),

library/std/src/sys/pal/common/tests.rs

@@ -7,7 +7,7 @@ use core::iter::repeat;
 #[test]
 fn stack_allocation_works() {
     let path = Path::new("abc");
-    let result = run_path_with_cstr(path, |p| {
+    let result = run_path_with_cstr(path, &|p| {
         assert_eq!(p, &*CString::new(path.as_os_str().as_encoded_bytes()).unwrap());
         Ok(42)
     });
@@ -17,14 +17,14 @@ fn stack_allocation_works() {
 #[test]
 fn stack_allocation_fails() {
     let path = Path::new("ab\0");
-    assert!(run_path_with_cstr::<(), _>(path, |_| unreachable!()).is_err());
+    assert!(run_path_with_cstr::<()>(path, &|_| unreachable!()).is_err());
 }
 
 #[test]
 fn heap_allocation_works() {
     let path = repeat("a").take(384).collect::<String>();
     let path = Path::new(&path);
-    let result = run_path_with_cstr(path, |p| {
+    let result = run_path_with_cstr(path, &|p| {
         assert_eq!(p, &*CString::new(path.as_os_str().as_encoded_bytes()).unwrap());
         Ok(42)
     });
@@ -36,15 +36,15 @@ fn heap_allocation_fails() {
     let mut path = repeat("a").take(384).collect::<String>();
     path.push('\0');
     let path = Path::new(&path);
-    assert!(run_path_with_cstr::<(), _>(path, |_| unreachable!()).is_err());
+    assert!(run_path_with_cstr::<()>(path, &|_| unreachable!()).is_err());
 }
 
 #[bench]
 fn bench_stack_path_alloc(b: &mut test::Bencher) {
     let path = repeat("a").take(383).collect::<String>();
     let p = Path::new(&path);
     b.iter(|| {
-        run_path_with_cstr(p, |cstr| {
+        run_path_with_cstr(p, &|cstr| {
             black_box(cstr);
             Ok(())
         })
@@ -57,7 +57,7 @@ fn bench_heap_path_alloc(b: &mut test::Bencher) {
     let path = repeat("a").take(384).collect::<String>();
     let p = Path::new(&path);
     b.iter(|| {
-        run_path_with_cstr(p, |cstr| {
+        run_path_with_cstr(p, &|cstr| {
             black_box(cstr);
             Ok(())
         })

library/std/src/sys/pal/hermit/fs.rs

@@ -269,7 +269,7 @@ impl OpenOptions {
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
-        run_path_with_cstr(path, |path| File::open_c(&path, opts))
+        run_path_with_cstr(path, &|path| File::open_c(&path, opts))
     }
 
     pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
@@ -421,7 +421,7 @@ pub fn readdir(_p: &Path) -> io::Result<ReadDir> {
 }
 
 pub fn unlink(path: &Path) -> io::Result<()> {
-    run_path_with_cstr(path, |path| cvt(unsafe { abi::unlink(path.as_ptr()) }).map(|_| ()))
+    run_path_with_cstr(path, &|path| cvt(unsafe { abi::unlink(path.as_ptr()) }).map(|_| ()))
 }
 
 pub fn rename(_old: &Path, _new: &Path) -> io::Result<()> {

library/std/src/sys/pal/solid/os.rs

@@ -172,7 +172,7 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    run_with_cstr(k.as_bytes(), |k| {
+    run_with_cstr(k.as_bytes(), &|k| {
         let _guard = env_read_lock();
         let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
 
@@ -190,16 +190,16 @@ pub fn getenv(k: &OsStr) -> Option<OsString> {
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    run_with_cstr(k.as_bytes(), |k| {
-        run_with_cstr(v.as_bytes(), |v| {
+    run_with_cstr(k.as_bytes(), &|k| {
+        run_with_cstr(v.as_bytes(), &|v| {
             let _guard = ENV_LOCK.write();
             cvt_env(unsafe { libc::setenv(k.as_ptr(), v.as_ptr(), 1) }).map(drop)
         })
     })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    run_with_cstr(n.as_bytes(), |nbuf| {
+    run_with_cstr(n.as_bytes(), &|nbuf| {
         let _guard = ENV_LOCK.write();
         cvt_env(unsafe { libc::unsetenv(nbuf.as_ptr()) }).map(drop)
     })

library/std/src/sys/pal/unix/fs.rs

@@ -1118,7 +1118,7 @@ impl OpenOptions {
 
 impl File {
     pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
-        run_path_with_cstr(path, |path| File::open_c(path, opts))
+        run_path_with_cstr(path, &|path| File::open_c(path, opts))
     }
 
     pub fn open_c(path: &CStr, opts: &OpenOptions) -> io::Result<File> {
@@ -1394,7 +1394,7 @@ impl DirBuilder {
     }
 
     pub fn mkdir(&self, p: &Path) -> io::Result<()> {
-        run_path_with_cstr(p, |p| cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) }).map(|_| ()))
+        run_path_with_cstr(p, &|p| cvt(unsafe { libc::mkdir(p.as_ptr(), self.mode) }).map(|_| ()))
     }
 
     pub fn set_mode(&mut self, mode: u32) {
@@ -1575,7 +1575,7 @@ impl fmt::Debug for File {
 }
 
 pub fn readdir(path: &Path) -> io::Result<ReadDir> {
-    let ptr = run_path_with_cstr(path, |p| unsafe { Ok(libc::opendir(p.as_ptr())) })?;
+    let ptr = run_path_with_cstr(path, &|p| unsafe { Ok(libc::opendir(p.as_ptr())) })?;
     if ptr.is_null() {
         Err(Error::last_os_error())
     } else {
@@ -1586,27 +1586,27 @@ pub fn readdir(path: &Path) -> io::Result<ReadDir> {
 }
 
 pub fn unlink(p: &Path) -> io::Result<()> {
-    run_path_with_cstr(p, |p| cvt(unsafe { libc::unlink(p.as_ptr()) }).map(|_| ()))
+    run_path_with_cstr(p, &|p| cvt(unsafe { libc::unlink(p.as_ptr()) }).map(|_| ()))
 }
 
 pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
-    run_path_with_cstr(old, |old| {
-        run_path_with_cstr(new, |new| {
+    run_path_with_cstr(old, &|old| {
+        run_path_with_cstr(new, &|new| {
             cvt(unsafe { libc::rename(old.as_ptr(), new.as_ptr()) }).map(|_| ())
         })
     })
 }
 
 pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
-    run_path_with_cstr(p, |p| cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) }).map(|_| ()))
+    run_path_with_cstr(p, &|p| cvt_r(|| unsafe { libc::chmod(p.as_ptr(), perm.mode) }).map(|_| ()))
 }
 
 pub fn rmdir(p: &Path) -> io::Result<()> {
-    run_path_with_cstr(p, |p| cvt(unsafe { libc::rmdir(p.as_ptr()) }).map(|_| ()))
+    run_path_with_cstr(p, &|p| cvt(unsafe { libc::rmdir(p.as_ptr()) }).map(|_| ()))
 }
 
 pub fn readlink(p: &Path) -> io::Result<PathBuf> {
-    run_path_with_cstr(p, |c_path| {
+    run_path_with_cstr(p, &|c_path| {
         let p = c_path.as_ptr();
 
         let mut buf = Vec::with_capacity(256);
@@ -1635,16 +1635,16 @@ pub fn readlink(p: &Path) -> io::Result<PathBuf> {
 }
 
 pub fn symlink(original: &Path, link: &Path) -> io::Result<()> {
-    run_path_with_cstr(original, |original| {
-        run_path_with_cstr(link, |link| {
+    run_path_with_cstr(original, &|original| {
+        run_path_with_cstr(link, &|link| {
             cvt(unsafe { libc::symlink(original.as_ptr(), link.as_ptr()) }).map(|_| ())
         })
     })
 }
 
 pub fn link(original: &Path, link: &Path) -> io::Result<()> {
-    run_path_with_cstr(original, |original| {
-        run_path_with_cstr(link, |link| {
+    run_path_with_cstr(original, &|original| {
+        run_path_with_cstr(link, &|link| {
             cfg_if::cfg_if! {
                 if #[cfg(any(target_os = "vxworks", target_os = "redox", target_os = "android", target_os = "espidf", target_os = "horizon", target_os = "vita"))] {
                     // VxWorks, Redox and ESP-IDF lack `linkat`, so use `link` instead. POSIX leaves
@@ -1678,7 +1678,7 @@ pub fn link(original: &Path, link: &Path) -> io::Result<()> {
 }
 
 pub fn stat(p: &Path) -> io::Result<FileAttr> {
-    run_path_with_cstr(p, |p| {
+    run_path_with_cstr(p, &|p| {
         cfg_has_statx! {
             if let Some(ret) = unsafe { try_statx(
                 libc::AT_FDCWD,
@@ -1697,7 +1697,7 @@ pub fn stat(p: &Path) -> io::Result<FileAttr> {
 }
 
 pub fn lstat(p: &Path) -> io::Result<FileAttr> {
-    run_path_with_cstr(p, |p| {
+    run_path_with_cstr(p, &|p| {
         cfg_has_statx! {
             if let Some(ret) = unsafe { try_statx(
                 libc::AT_FDCWD,
@@ -1716,7 +1716,7 @@ pub fn lstat(p: &Path) -> io::Result<FileAttr> {
 }
 
 pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
-    let r = run_path_with_cstr(p, |path| unsafe {
+    let r = run_path_with_cstr(p, &|path| unsafe {
         Ok(libc::realpath(path.as_ptr(), ptr::null_mut()))
     })?;
     if r.is_null() {
@@ -1879,7 +1879,7 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     // Opportunistically attempt to create a copy-on-write clone of `from`
     // using `fclonefileat`.
     if HAS_FCLONEFILEAT.load(Ordering::Relaxed) {
-        let clonefile_result = run_path_with_cstr(to, |to| {
+        let clonefile_result = run_path_with_cstr(to, &|to| {
             cvt(unsafe { fclonefileat(reader.as_raw_fd(), libc::AT_FDCWD, to.as_ptr(), 0) })
         });
         match clonefile_result {
@@ -1925,7 +1925,7 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
 }
 
 pub fn chown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
-    run_path_with_cstr(path, |path| {
+    run_path_with_cstr(path, &|path| {
         cvt(unsafe { libc::chown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
             .map(|_| ())
     })
@@ -1937,15 +1937,15 @@ pub fn fchown(fd: c_int, uid: u32, gid: u32) -> io::Result<()> {
 }
 
 pub fn lchown(path: &Path, uid: u32, gid: u32) -> io::Result<()> {
-    run_path_with_cstr(path, |path| {
+    run_path_with_cstr(path, &|path| {
         cvt(unsafe { libc::lchown(path.as_ptr(), uid as libc::uid_t, gid as libc::gid_t) })
             .map(|_| ())
     })
 }
 
 #[cfg(not(any(target_os = "fuchsia", target_os = "vxworks")))]
 pub fn chroot(dir: &Path) -> io::Result<()> {
-    run_path_with_cstr(dir, |dir| cvt(unsafe { libc::chroot(dir.as_ptr()) }).map(|_| ()))
+    run_path_with_cstr(dir, &|dir| cvt(unsafe { libc::chroot(dir.as_ptr()) }).map(|_| ()))
 }
 
 pub use remove_dir_impl::remove_dir_all;
@@ -2140,7 +2140,7 @@ mod remove_dir_impl {
         if attr.file_type().is_symlink() {
             crate::fs::remove_file(p)
         } else {
-            run_path_with_cstr(p, |p| remove_dir_all_recursive(None, &p))
+            run_path_with_cstr(p, &|p| remove_dir_all_recursive(None, &p))
         }
     }
 

library/std/src/sys/pal/unix/os.rs

@@ -186,7 +186,7 @@ pub fn chdir(_p: &path::Path) -> io::Result<()> {
 
 #[cfg(not(target_os = "espidf"))]
 pub fn chdir(p: &path::Path) -> io::Result<()> {
-    let result = run_path_with_cstr(p, |p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
+    let result = run_path_with_cstr(p, &|p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
     if result == 0 { Ok(()) } else { Err(io::Error::last_os_error()) }
 }
 
@@ -643,7 +643,7 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    run_with_cstr(k.as_bytes(), |k| {
+    run_with_cstr(k.as_bytes(), &|k| {
         let _guard = env_read_lock();
         let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
 
@@ -661,16 +661,16 @@ pub fn getenv(k: &OsStr) -> Option<OsString> {
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    run_with_cstr(k.as_bytes(), |k| {
-        run_with_cstr(v.as_bytes(), |v| {
+    run_with_cstr(k.as_bytes(), &|k| {
+        run_with_cstr(v.as_bytes(), &|v| {
             let _guard = ENV_LOCK.write();
             cvt(unsafe { libc::setenv(k.as_ptr(), v.as_ptr(), 1) }).map(drop)
         })
     })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    run_with_cstr(n.as_bytes(), |nbuf| {
+    run_with_cstr(n.as_bytes(), &|nbuf| {
         let _guard = ENV_LOCK.write();
         cvt(unsafe { libc::unsetenv(nbuf.as_ptr()) }).map(drop)
     })

library/std/src/sys/pal/wasi/fs.rs

@@ -698,7 +698,7 @@ fn open_at(fd: &WasiFd, path: &Path, opts: &OpenOptions) -> io::Result<File> {
 /// Note that this can fail if `p` doesn't look like it can be opened relative
 /// to any pre-opened file descriptor.
 fn open_parent(p: &Path) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
-    run_path_with_cstr(p, |p| {
+    run_path_with_cstr(p, &|p| {
         let mut buf = Vec::<u8>::with_capacity(512);
         loop {
             unsafe {

library/std/src/sys/pal/wasi/os.rs

@@ -95,7 +95,7 @@ pub fn getcwd() -> io::Result<PathBuf> {
 }
 
 pub fn chdir(p: &path::Path) -> io::Result<()> {
-    let result = run_path_with_cstr(p, |p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
+    let result = run_path_with_cstr(p, &|p| unsafe { Ok(libc::chdir(p.as_ptr())) })?;
     match result == (0 as libc::c_int) {
         true => Ok(()),
         false => Err(io::Error::last_os_error()),
@@ -227,7 +227,7 @@ pub fn env() -> Env {
 pub fn getenv(k: &OsStr) -> Option<OsString> {
     // environment variables with a nul byte can't be set, so their value is
     // always None as well
-    run_with_cstr(k.as_bytes(), |k| {
+    run_with_cstr(k.as_bytes(), &|k| {
         let _guard = env_read_lock();
         let v = unsafe { libc::getenv(k.as_ptr()) } as *const libc::c_char;
 
@@ -245,16 +245,16 @@ pub fn getenv(k: &OsStr) -> Option<OsString> {
 }
 
 pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
-    run_with_cstr(k.as_bytes(), |k| {
-        run_with_cstr(v.as_bytes(), |v| unsafe {
+    run_with_cstr(k.as_bytes(), &|k| {
+        run_with_cstr(v.as_bytes(), &|v| unsafe {
             let _guard = env_write_lock();
             cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(drop)
         })
     })
 }
 
 pub fn unsetenv(n: &OsStr) -> io::Result<()> {
-    run_with_cstr(n.as_bytes(), |nbuf| unsafe {
+    run_with_cstr(n.as_bytes(), &|nbuf| unsafe {
         let _guard = env_write_lock();
         cvt(libc::unsetenv(nbuf.as_ptr())).map(drop)
     })

library/std/src/sys_common/net.rs

@@ -199,7 +199,7 @@ impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
     fn try_from((host, port): (&'a str, u16)) -> io::Result<LookupHost> {
         init();
 
-        run_with_cstr(host.as_bytes(), |c_host| {
+        run_with_cstr(host.as_bytes(), &|c_host| {
             let mut hints: c::addrinfo = unsafe { mem::zeroed() };
             hints.ai_socktype = c::SOCK_STREAM;
             let mut res = ptr::null_mut();