Win: Use FILE_RENAME_FLAG_POSIX_SEMANTICS for std::fs::rename if …

…available

Windows 10 1601 introduced `FileRenameInfoEx` as well as
`FILE_RENAME_FLAG_POSIX_SEMANTICS`, allowing for atomic renaming. If it
isn't supported, we fall back to `FileRenameInfo`.

This commit also replicates `MoveFileExW`'s behavior of checking whether
the source file is a mount point and moving the mount point instead of
resolving the target path.

std/src/fs.rs

@@ -2397,12 +2397,14 @@ pub fn symlink_metadata<P: AsRef<Path>>(path: P) -> io::Result<Metadata> {
 /// # Platform-specific behavior
 ///
 /// This function currently corresponds to the `rename` function on Unix
-/// and the `MoveFileEx` function with the `MOVEFILE_REPLACE_EXISTING` flag on Windows.
+/// and the `SetFileInformationByHandle` function on Windows.
 ///
 /// Because of this, the behavior when both `from` and `to` exist differs. On
 /// Unix, if `from` is a directory, `to` must also be an (empty) directory. If
-/// `from` is not a directory, `to` must also be not a directory. In contrast,
-/// on Windows, `from` can be anything, but `to` must *not* be a directory.
+/// `from` is not a directory, `to` must also be not a directory. The behavior
+/// on Windows is the same on Windows 10 1607 and higher if `FileRenameInfoEx`
+/// is supported by the filesystem; otherwise, `from` can be anything, but
+/// `to` must *not* be a directory.
 ///
 /// Note that, this [may change in the future][changes].
 ///

std/src/sys/pal/windows/c/bindings.txt

@@ -2295,6 +2295,7 @@ Windows.Win32.Storage.FileSystem.FILE_NAME_OPENED
 Windows.Win32.Storage.FileSystem.FILE_READ_ATTRIBUTES
 Windows.Win32.Storage.FileSystem.FILE_READ_DATA
 Windows.Win32.Storage.FileSystem.FILE_READ_EA
+Windows.Win32.Storage.FileSystem.FILE_RENAME_INFO
 Windows.Win32.Storage.FileSystem.FILE_SHARE_DELETE
 Windows.Win32.Storage.FileSystem.FILE_SHARE_MODE
 Windows.Win32.Storage.FileSystem.FILE_SHARE_NONE
@@ -2603,5 +2604,7 @@ Windows.Win32.System.Threading.WaitForMultipleObjects
 Windows.Win32.System.Threading.WaitForSingleObject
 Windows.Win32.System.Threading.WakeAllConditionVariable
 Windows.Win32.System.Threading.WakeConditionVariable
+Windows.Win32.System.WindowsProgramming.FILE_RENAME_FLAG_POSIX_SEMANTICS
+Windows.Win32.System.WindowsProgramming.FILE_RENAME_FLAG_REPLACE_IF_EXISTS
 Windows.Win32.System.WindowsProgramming.PROGRESS_CONTINUE
 Windows.Win32.UI.Shell.GetUserProfileDirectoryW

std/src/sys/pal/windows/c/windows_sys.rs

@@ -2472,6 +2472,22 @@ pub const FILE_RANDOM_ACCESS: NTCREATEFILE_CREATE_OPTIONS = 2048u32;
 pub const FILE_READ_ATTRIBUTES: FILE_ACCESS_RIGHTS = 128u32;
 pub const FILE_READ_DATA: FILE_ACCESS_RIGHTS = 1u32;
 pub const FILE_READ_EA: FILE_ACCESS_RIGHTS = 8u32;
+pub const FILE_RENAME_FLAG_POSIX_SEMANTICS: u32 = 2u32;
+pub const FILE_RENAME_FLAG_REPLACE_IF_EXISTS: u32 = 1u32;
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct FILE_RENAME_INFO {
+    pub Anonymous: FILE_RENAME_INFO_0,
+    pub RootDirectory: HANDLE,
+    pub FileNameLength: u32,
+    pub FileName: [u16; 1],
+}
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub union FILE_RENAME_INFO_0 {
+    pub ReplaceIfExists: BOOLEAN,
+    pub Flags: u32,
+}
 pub const FILE_RESERVE_OPFILTER: NTCREATEFILE_CREATE_OPTIONS = 1048576u32;
 pub const FILE_SEQUENTIAL_ONLY: NTCREATEFILE_CREATE_OPTIONS = 4u32;
 pub const FILE_SESSION_AWARE: NTCREATEFILE_CREATE_OPTIONS = 262144u32;

std/src/sys/pal/windows/fs.rs

@@ -1,5 +1,6 @@
 use super::api::{self, WinError};
 use super::{IoResult, to_u16s};
+use crate::alloc::{alloc, handle_alloc_error};
 use crate::borrow::Cow;
 use crate::ffi::{OsStr, OsString, c_void};
 use crate::io::{self, BorrowedCursor, Error, IoSlice, IoSliceMut, SeekFrom};
@@ -1223,7 +1224,149 @@ pub fn unlink(p: &Path) -> io::Result<()> {
 pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
     let old = maybe_verbatim(old)?;
     let new = maybe_verbatim(new)?;
-    cvt(unsafe { c::MoveFileExW(old.as_ptr(), new.as_ptr(), c::MOVEFILE_REPLACE_EXISTING) })?;
+
+    let new_len_without_nul_in_bytes = (new.len() - 1).try_into().unwrap();
+
+    let struct_size = mem::size_of::<c::FILE_RENAME_INFO>() - mem::size_of::<u16>()
+        + new.len() * mem::size_of::<u16>();
+
+    let struct_size: u32 = struct_size.try_into().unwrap();
+
+    let create_file = |extra_access, extra_flags| {
+        let handle = unsafe {
+            HandleOrInvalid::from_raw_handle(c::CreateFileW(
+                old.as_ptr(),
+                c::SYNCHRONIZE | c::DELETE | extra_access,
+                c::FILE_SHARE_READ | c::FILE_SHARE_WRITE | c::FILE_SHARE_DELETE,
+                ptr::null(),
+                c::OPEN_EXISTING,
+                c::FILE_ATTRIBUTE_NORMAL | c::FILE_FLAG_BACKUP_SEMANTICS | extra_flags,
+                ptr::null_mut(),
+            ))
+        };
+
+        OwnedHandle::try_from(handle).map_err(|_| io::Error::last_os_error())
+    };
+
+    // The following code replicates `MoveFileEx`'s behavior as reverse-engineered from its disassembly.
+    // If `old` refers to a mount point, we move it instead of the target.
+    let handle = match create_file(c::FILE_READ_ATTRIBUTES, c::FILE_FLAG_OPEN_REPARSE_POINT) {
+        Ok(handle) => {
+            let mut file_attribute_tag_info: MaybeUninit<c::FILE_ATTRIBUTE_TAG_INFO> =
+                MaybeUninit::uninit();
+
+            let result = unsafe {
+                cvt(c::GetFileInformationByHandleEx(
+                    handle.as_raw_handle(),
+                    c::FileAttributeTagInfo,
+                    file_attribute_tag_info.as_mut_ptr().cast(),
+                    mem::size_of::<c::FILE_ATTRIBUTE_TAG_INFO>().try_into().unwrap(),
+                ))
+            };
+
+            if let Err(err) = result {
+                if err.raw_os_error() == Some(c::ERROR_INVALID_PARAMETER as _)
+                    || err.raw_os_error() == Some(c::ERROR_INVALID_FUNCTION as _)
+                {
+                    // `GetFileInformationByHandleEx` documents that not all underlying drivers support all file information classes.
+                    // Since we know we passed the correct arguments, this means the underlying driver didn't understand our request;
+                    // `MoveFileEx` proceeds by reopening the file without inhibiting reparse point behavior.
+                    None
+                } else {
+                    Some(Err(err))
+                }
+            } else {
+                // SAFETY: The struct has been initialized by GetFileInformationByHandleEx
+                let file_attribute_tag_info = unsafe { file_attribute_tag_info.assume_init() };
+
+                if file_attribute_tag_info.FileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0
+                    && file_attribute_tag_info.ReparseTag != c::IO_REPARSE_TAG_MOUNT_POINT
+                {
+                    // The file is not a mount point: Reopen the file without inhibiting reparse point behavior.
+                    None
+                } else {
+                    // The file is a mount point: Don't reopen the file so that the mount point gets renamed.
+                    Some(Ok(handle))
+                }
+            }
+        }
+        // The underlying driver may not support `FILE_FLAG_OPEN_REPARSE_POINT`: Retry without it.
+        Err(err) if err.raw_os_error() == Some(c::ERROR_INVALID_PARAMETER as _) => None,
+        Err(err) => Some(Err(err)),
+    }
+    .unwrap_or_else(|| create_file(0, 0))?;
+
+    // The last field of FILE_RENAME_INFO, the file name, is unsized.
+    // Therefore we need to subtract the size of one wide char.
+    let layout = core::alloc::Layout::from_size_align(
+        struct_size as _,
+        mem::align_of::<c::FILE_RENAME_INFO>(),
+    )
+    .unwrap();
+
+    let file_rename_info = unsafe { alloc(layout) } as *mut c::FILE_RENAME_INFO;
+
+    if file_rename_info.is_null() {
+        handle_alloc_error(layout);
+    }
+
+    // SAFETY: file_rename_info is a non-null pointer pointing to memory allocated by the global allocator.
+    let mut file_rename_info = unsafe { Box::from_raw(file_rename_info) };
+
+    // SAFETY: We have allocated enough memory for a full FILE_RENAME_INFO struct and a filename.
+    unsafe {
+        (&raw mut (*file_rename_info).Anonymous).write(c::FILE_RENAME_INFO_0 {
+            // Don't bother with FileRenameInfo on Windows 7 since it doesn't exist.
+            #[cfg(not(target_vendor = "win7"))]
+            Flags: c::FILE_RENAME_FLAG_REPLACE_IF_EXISTS | c::FILE_RENAME_FLAG_POSIX_SEMANTICS,
+            #[cfg(target_vendor = "win7")]
+            ReplaceIfExists: 1,
+        });
+
+        (&raw mut (*file_rename_info).RootDirectory).write(ptr::null_mut());
+        (&raw mut (*file_rename_info).FileNameLength).write(new_len_without_nul_in_bytes);
+
+        new.as_ptr()
+            .copy_to_nonoverlapping((&raw mut (*file_rename_info).FileName) as *mut u16, new.len());
+    }
+
+    #[cfg(not(target_vendor = "win7"))]
+    const FileInformationClass: c::FILE_INFO_BY_HANDLE_CLASS = c::FileRenameInfoEx;
+    #[cfg(target_vendor = "win7")]
+    const FileInformationClass: c::FILE_INFO_BY_HANDLE_CLASS = c::FileRenameInfo;
+
+    // We don't use `set_file_information_by_handle` here as `FILE_RENAME_INFO` is used for both `FileRenameInfo` and `FileRenameInfoEx`.
+    let result = unsafe {
+        cvt(c::SetFileInformationByHandle(
+            handle.as_raw_handle(),
+            FileInformationClass,
+            (&raw const *file_rename_info).cast::<c_void>(),
+            struct_size,
+        ))
+    };
+
+    #[cfg(not(target_vendor = "win7"))]
+    if let Err(err) = result {
+        if err.raw_os_error() == Some(c::ERROR_INVALID_PARAMETER as _) {
+            // FileRenameInfoEx and FILE_RENAME_FLAG_POSIX_SEMANTICS were added in Windows 10 1607; retry with FileRenameInfo.
+            file_rename_info.Anonymous.ReplaceIfExists = 1;
+
+            cvt(unsafe {
+                c::SetFileInformationByHandle(
+                    handle.as_raw_handle(),
+                    c::FileRenameInfo,
+                    (&raw const *file_rename_info).cast::<c_void>(),
+                    struct_size,
+                )
+            })?;
+        } else {
+            return Err(err);
+        }
+    }
+
+    #[cfg(target_vendor = "win7")]
+    result?;
+
     Ok(())
 }