host_env: renameat support for os.rename (#8118)

Python's `os.rename` supports renaming a path relative to a directory
descriptor - essentially, `renameat`. The syscall and its Rustix wrapper
does all of the work, so this patch mainly updates the Python signature
to forward to the implementation.

As of this patch, `os.rename` is still incorrect for Windows because it
always replaces the destination file. I added a small note for future
contributors (or myself, since I might tackle it) as a reminder of
what's broken.

crates/host_env/src/os.rs

@@ -1,7 +1,6 @@
 // spell-checker:disable
 // TODO: we can move more os-specific bindings/interfaces from stdlib::{os, posix, nt} to here
 
-#[cfg(any(unix, windows, target_os = "wasi"))]
 use crate::crt_fd;
 #[cfg(windows)]
 use crate::fs;
@@ -10,6 +9,8 @@ use core::ffi::CStr;
 use core::str::Utf8Error;
 #[cfg(windows)]
 use core::time::Duration;
+#[cfg(unix)]
+use rustix::fd::AsFd;
 use std::{
     env,
     ffi::{OsStr, OsString},
@@ -266,11 +267,39 @@ pub fn copy_file_range(
     rustix::fs::copy_file_range(src, offset_src, dst, offset_dst, count)
 }
 
+#[cfg(not(unix))]
 pub fn rename(
     from: impl AsRef<std::path::Path>,
+    from_fd: Option<crt_fd::Borrowed<'_>>,
     to: impl AsRef<std::path::Path>,
+    to_fd: Option<crt_fd::Borrowed<'_>>,
 ) -> io::Result<()> {
-    std::fs::rename(from, to)
+    if from_fd.is_none() && to_fd.is_none() {
+        // TODO: Rust's implementation always overwrites the file so ensure consistency between
+        // operating systems. We need to use windows-sys directly to distinguish between
+        // os.rename and os.replace.
+        std::fs::rename(from, to)
+    } else {
+        core::hint::cold_path();
+        Err(io::Error::new(
+            io::ErrorKind::Unsupported,
+            "renameat is not available on this platform",
+        ))
+    }
+}
+
+#[cfg(unix)]
+pub fn rename(
+    from: impl AsRef<std::path::Path>,
+    from_fd: Option<crt_fd::Borrowed<'_>>,
+    to: impl AsRef<std::path::Path>,
+    to_fd: Option<crt_fd::Borrowed<'_>>,
+) -> io::Result<()> {
+    let from = from.as_ref();
+    let from_fd = from_fd.as_ref().map_or(rustix::fs::CWD, AsFd::as_fd);
+    let to = to.as_ref();
+    let to_fd = to_fd.as_ref().map_or(rustix::fs::CWD, AsFd::as_fd);
+    rustix::fs::renameat(from_fd, from, to_fd, to).map_err(Into::into)
 }
 
 #[cfg(windows)]

crates/vm/src/stdlib/os.rs

@@ -189,6 +189,7 @@ pub(super) mod _os {
     const UTIME_DIR_FD: bool = cfg!(not(any(windows, target_os = "redox")));
     pub(crate) const SYMLINK_DIR_FD: bool = cfg!(not(any(windows, target_os = "redox")));
     pub(crate) const UNLINK_DIR_FD: bool = cfg!(not(any(windows, target_os = "redox")));
+    const RENAME_DIR_FD: bool = cfg!(unix);
     const RMDIR_DIR_FD: bool = cfg!(not(any(windows, target_os = "redox")));
     const SCANDIR_FD: bool = cfg!(all(unix, not(target_os = "redox")));
 
@@ -1377,19 +1378,37 @@ pub(super) mod _os {
         FsPath::try_from_path_like(path, false, vm)
     }
 
+    #[derive(FromArgs)]
+    struct RenameArgs<'fd> {
+        #[pyarg(positional)]
+        src: PyObjectRef,
+        #[pyarg(positional)]
+        dst: PyObjectRef,
+        #[pyarg(any, default)]
+        src_dir_fd: OptionalArg<crt_fd::Borrowed<'fd>>,
+        #[pyarg(any, default)]
+        dst_dir_fd: OptionalArg<crt_fd::Borrowed<'fd>>,
+    }
+
     #[pyfunction]
     #[pyfunction(name = "replace")]
-    fn rename(src: PyObjectRef, dst: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+    fn rename(args: RenameArgs<'_>, vm: &VirtualMachine) -> PyResult<()> {
         let src = PathConverter::new()
             .function("rename")
             .argument("src")
-            .try_path(src, vm)?;
+            .try_path(args.src, vm)?;
         let dst = PathConverter::new()
             .function("rename")
             .argument("dst")
-            .try_path(dst, vm)?;
+            .try_path(args.dst, vm)?;
 
-        crate::host_env::os::rename(&src.path, &dst.path).map_err(|err| {
+        crate::host_env::os::rename(
+            &src,
+            args.src_dir_fd.into_option(),
+            &dst,
+            args.dst_dir_fd.into_option(),
+        )
+        .map_err(|err| {
             let builder = err.to_os_error_builder(vm);
             let builder = builder.filename(src.filename(vm));
             let builder = builder.filename2(dst.filename(vm));
@@ -1932,8 +1951,8 @@ pub(super) mod _os {
             SupportFunc::new("readlink", Some(false), None, Some(false)),
             SupportFunc::new("remove", Some(false), Some(UNLINK_DIR_FD), Some(false)),
             SupportFunc::new("unlink", Some(false), Some(UNLINK_DIR_FD), Some(false)),
-            SupportFunc::new("rename", Some(false), None, Some(false)),
-            SupportFunc::new("replace", Some(false), None, Some(false)), // TODO: Fix replace
+            SupportFunc::new("rename", Some(false), Some(RENAME_DIR_FD), Some(false)),
+            SupportFunc::new("replace", Some(false), Some(RENAME_DIR_FD), Some(false)), // TODO: Fix replace
             SupportFunc::new("rmdir", Some(false), Some(RMDIR_DIR_FD), Some(false)),
             SupportFunc::new("scandir", Some(SCANDIR_FD), Some(false), Some(false)),
             SupportFunc::new("stat", Some(true), Some(STAT_DIR_FD), Some(true)),