std: move path into `sys`

6 files changed, 612 insertions, 0 deletions

diff --git a/library/std/src/sys/path/mod.rs b/library/std/src/sys/path/mod.rs
new file mode 100644
index 00000000000..24a94ec7828
--- /dev/null
+++ b/library/std/src/sys/path/mod.rs
@@ -0,0 +1,18 @@
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "windows")] {
+        mod windows;
+        pub use windows::*;
+    } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
+        mod sgx;
+        pub use sgx::*;
+    } else if #[cfg(any(
+        target_os = "uefi",
+        target_os = "solid_asp3",
+    ))] {
+        mod unsupported_backslash;
+        pub use unsupported_backslash::*;
+    } else {
+        mod unix;
+        pub use unix::*;
+    }
+}
diff --git a/library/std/src/sys/path/sgx.rs b/library/std/src/sys/path/sgx.rs
new file mode 100644
index 00000000000..c805c15e702
--- /dev/null
+++ b/library/std/src/sys/path/sgx.rs
@@ -0,0 +1,25 @@
+use crate::ffi::OsStr;
+use crate::io;
+use crate::path::{Path, PathBuf, Prefix};
+use crate::sys::unsupported;
+
+#[inline]
+pub fn is_sep_byte(b: u8) -> bool {
+    b == b'/'
+}
+
+#[inline]
+pub fn is_verbatim_sep(b: u8) -> bool {
+    b == b'/'
+}
+
+pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
+    None
+}
+
+pub const MAIN_SEP_STR: &str = "/";
+pub const MAIN_SEP: char = '/';
+
+pub(crate) fn absolute(_path: &Path) -> io::Result<PathBuf> {
+    unsupported()
+}
diff --git a/library/std/src/sys/path/unix.rs b/library/std/src/sys/path/unix.rs
new file mode 100644
index 00000000000..837f68d3eaf
--- /dev/null
+++ b/library/std/src/sys/path/unix.rs
@@ -0,0 +1,63 @@
+use crate::env;
+use crate::ffi::OsStr;
+use crate::io;
+use crate::path::{Path, PathBuf, Prefix};
+
+#[inline]
+pub fn is_sep_byte(b: u8) -> bool {
+    b == b'/'
+}
+
+#[inline]
+pub fn is_verbatim_sep(b: u8) -> bool {
+    b == b'/'
+}
+
+#[inline]
+pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
+    None
+}
+
+pub const MAIN_SEP_STR: &str = "/";
+pub const MAIN_SEP: char = '/';
+
+/// Make a POSIX path absolute without changing its semantics.
+pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
+    // This is mostly a wrapper around collecting `Path::components`, with
+    // exceptions made where this conflicts with the POSIX specification.
+    // See 4.13 Pathname Resolution, IEEE Std 1003.1-2017
+    // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
+
+    // Get the components, skipping the redundant leading "." component if it exists.
+    let mut components = path.strip_prefix(".").unwrap_or(path).components();
+    let path_os = path.as_os_str().as_encoded_bytes();
+
+    let mut normalized = if path.is_absolute() {
+        // "If a pathname begins with two successive <slash> characters, the
+        // first component following the leading <slash> characters may be
+        // interpreted in an implementation-defined manner, although more than
+        // two leading <slash> characters shall be treated as a single <slash>
+        // character."
+        if path_os.starts_with(b"//") && !path_os.starts_with(b"///") {
+            components.next();
+            PathBuf::from("//")
+        } else {
+            PathBuf::new()
+        }
+    } else {
+        env::current_dir()?
+    };
+    normalized.extend(components);
+
+    // "Interfaces using pathname resolution may specify additional constraints
+    // when a pathname that does not name an existing directory contains at
+    // least one non- <slash> character and contains one or more trailing
+    // <slash> characters".
+    // A trailing <slash> is also meaningful if "a symbolic link is
+    // encountered during pathname resolution".
+    if path_os.ends_with(b"/") {
+        normalized.push("");
+    }
+
+    Ok(normalized)
+}
diff --git a/library/std/src/sys/path/unsupported_backslash.rs b/library/std/src/sys/path/unsupported_backslash.rs
new file mode 100644
index 00000000000..7045c9be25b
--- /dev/null
+++ b/library/std/src/sys/path/unsupported_backslash.rs
@@ -0,0 +1,25 @@
+use crate::ffi::OsStr;
+use crate::io;
+use crate::path::{Path, PathBuf, Prefix};
+use crate::sys::unsupported;
+
+#[inline]
+pub fn is_sep_byte(b: u8) -> bool {
+    b == b'\\'
+}
+
+#[inline]
+pub fn is_verbatim_sep(b: u8) -> bool {
+    b == b'\\'
+}
+
+pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
+    None
+}
+
+pub const MAIN_SEP_STR: &str = "\\";
+pub const MAIN_SEP: char = '\\';
+
+pub(crate) fn absolute(_path: &Path) -> io::Result<PathBuf> {
+    unsupported()
+}
diff --git a/library/std/src/sys/path/windows.rs b/library/std/src/sys/path/windows.rs
new file mode 100644
index 00000000000..cebc7910231
--- /dev/null
+++ b/library/std/src/sys/path/windows.rs
@@ -0,0 +1,344 @@
+use crate::ffi::{OsStr, OsString};
+use crate::io;
+use crate::path::{Path, PathBuf, Prefix};
+use crate::ptr;
+use crate::sys::pal::{c, fill_utf16_buf, os2path, to_u16s};
+
+#[cfg(test)]
+mod tests;
+
+pub const MAIN_SEP_STR: &str = "\\";
+pub const MAIN_SEP: char = '\\';
+
+#[inline]
+pub fn is_sep_byte(b: u8) -> bool {
+    b == b'/' || b == b'\\'
+}
+
+#[inline]
+pub fn is_verbatim_sep(b: u8) -> bool {
+    b == b'\\'
+}
+
+/// Returns true if `path` looks like a lone filename.
+pub(crate) fn is_file_name(path: &OsStr) -> bool {
+    !path.as_encoded_bytes().iter().copied().any(is_sep_byte)
+}
+pub(crate) fn has_trailing_slash(path: &OsStr) -> bool {
+    let is_verbatim = path.as_encoded_bytes().starts_with(br"\\?\");
+    let is_separator = if is_verbatim { is_verbatim_sep } else { is_sep_byte };
+    if let Some(&c) = path.as_encoded_bytes().last() { is_separator(c) } else { false }
+}
+
+/// Appends a suffix to a path.
+///
+/// Can be used to append an extension without removing an existing extension.
+pub(crate) fn append_suffix(path: PathBuf, suffix: &OsStr) -> PathBuf {
+    let mut path = OsString::from(path);
+    path.push(suffix);
+    path.into()
+}
+
+struct PrefixParser<'a, const LEN: usize> {
+    path: &'a OsStr,
+    prefix: [u8; LEN],
+}
+
+impl<'a, const LEN: usize> PrefixParser<'a, LEN> {
+    #[inline]
+    fn get_prefix(path: &OsStr) -> [u8; LEN] {
+        let mut prefix = [0; LEN];
+        // SAFETY: Only ASCII characters are modified.
+        for (i, &ch) in path.as_encoded_bytes().iter().take(LEN).enumerate() {
+            prefix[i] = if ch == b'/' { b'\\' } else { ch };
+        }
+        prefix
+    }
+
+    fn new(path: &'a OsStr) -> Self {
+        Self { path, prefix: Self::get_prefix(path) }
+    }
+
+    fn as_slice(&self) -> PrefixParserSlice<'a, '_> {
+        PrefixParserSlice {
+            path: self.path,
+            prefix: &self.prefix[..LEN.min(self.path.len())],
+            index: 0,
+        }
+    }
+}
+
+struct PrefixParserSlice<'a, 'b> {
+    path: &'a OsStr,
+    prefix: &'b [u8],
+    index: usize,
+}
+
+impl<'a> PrefixParserSlice<'a, '_> {
+    fn strip_prefix(&self, prefix: &str) -> Option<Self> {
+        self.prefix[self.index..]
+            .starts_with(prefix.as_bytes())
+            .then_some(Self { index: self.index + prefix.len(), ..*self })
+    }
+
+    fn prefix_bytes(&self) -> &'a [u8] {
+        &self.path.as_encoded_bytes()[..self.index]
+    }
+
+    fn finish(self) -> &'a OsStr {
+        // SAFETY: The unsafety here stems from converting between &OsStr and
+        // &[u8] and back. This is safe to do because (1) we only look at ASCII
+        // contents of the encoding and (2) new &OsStr values are produced only
+        // from ASCII-bounded slices of existing &OsStr values.
+        unsafe { OsStr::from_encoded_bytes_unchecked(&self.path.as_encoded_bytes()[self.index..]) }
+    }
+}
+
+pub fn parse_prefix(path: &OsStr) -> Option<Prefix<'_>> {
+    use Prefix::{DeviceNS, Disk, Verbatim, VerbatimDisk, VerbatimUNC, UNC};
+
+    let parser = PrefixParser::<8>::new(path);
+    let parser = parser.as_slice();
+    if let Some(parser) = parser.strip_prefix(r"\\") {
+        // \\
+
+        // The meaning of verbatim paths can change when they use a different
+        // separator.
+        if let Some(parser) = parser.strip_prefix(r"?\")
+            && !parser.prefix_bytes().iter().any(|&x| x == b'/')
+        {
+            // \\?\
+            if let Some(parser) = parser.strip_prefix(r"UNC\") {
+                // \\?\UNC\server\share
+
+                let path = parser.finish();
+                let (server, path) = parse_next_component(path, true);
+                let (share, _) = parse_next_component(path, true);
+
+                Some(VerbatimUNC(server, share))
+            } else {
+                let path = parser.finish();
+
+                // in verbatim paths only recognize an exact drive prefix
+                if let Some(drive) = parse_drive_exact(path) {
+                    // \\?\C:
+                    Some(VerbatimDisk(drive))
+                } else {
+                    // \\?\prefix
+                    let (prefix, _) = parse_next_component(path, true);
+                    Some(Verbatim(prefix))
+                }
+            }
+        } else if let Some(parser) = parser.strip_prefix(r".\") {
+            // \\.\COM42
+            let path = parser.finish();
+            let (prefix, _) = parse_next_component(path, false);
+            Some(DeviceNS(prefix))
+        } else {
+            let path = parser.finish();
+            let (server, path) = parse_next_component(path, false);
+            let (share, _) = parse_next_component(path, false);
+
+            if !server.is_empty() && !share.is_empty() {
+                // \\server\share
+                Some(UNC(server, share))
+            } else {
+                // no valid prefix beginning with "\\" recognized
+                None
+            }
+        }
+    } else {
+        // If it has a drive like `C:` then it's a disk.
+        // Otherwise there is no prefix.
+        parse_drive(path).map(Disk)
+    }
+}
+
+// Parses a drive prefix, e.g. "C:" and "C:\whatever"
+fn parse_drive(path: &OsStr) -> Option<u8> {
+    // In most DOS systems, it is not possible to have more than 26 drive letters.
+    // See <https://en.wikipedia.org/wiki/Drive_letter_assignment#Common_assignments>.
+    fn is_valid_drive_letter(drive: &u8) -> bool {
+        drive.is_ascii_alphabetic()
+    }
+
+    match path.as_encoded_bytes() {
+        [drive, b':', ..] if is_valid_drive_letter(drive) => Some(drive.to_ascii_uppercase()),
+        _ => None,
+    }
+}
+
+// Parses a drive prefix exactly, e.g. "C:"
+fn parse_drive_exact(path: &OsStr) -> Option<u8> {
+    // only parse two bytes: the drive letter and the drive separator
+    if path.as_encoded_bytes().get(2).map(|&x| is_sep_byte(x)).unwrap_or(true) {
+        parse_drive(path)
+    } else {
+        None
+    }
+}
+
+// Parse the next path component.
+//
+// Returns the next component and the rest of the path excluding the component and separator.
+// Does not recognize `/` as a separator character if `verbatim` is true.
+fn parse_next_component(path: &OsStr, verbatim: bool) -> (&OsStr, &OsStr) {
+    let separator = if verbatim { is_verbatim_sep } else { is_sep_byte };
+
+    match path.as_encoded_bytes().iter().position(|&x| separator(x)) {
+        Some(separator_start) => {
+            let separator_end = separator_start + 1;
+
+            let component = &path.as_encoded_bytes()[..separator_start];
+
+            // Panic safe
+            // The max `separator_end` is `bytes.len()` and `bytes[bytes.len()..]` is a valid index.
+            let path = &path.as_encoded_bytes()[separator_end..];
+
+            // SAFETY: `path` is a valid wtf8 encoded slice and each of the separators ('/', '\')
+            // is encoded in a single byte, therefore `bytes[separator_start]` and
+            // `bytes[separator_end]` must be code point boundaries and thus
+            // `bytes[..separator_start]` and `bytes[separator_end..]` are valid wtf8 slices.
+            unsafe {
+                (
+                    OsStr::from_encoded_bytes_unchecked(component),
+                    OsStr::from_encoded_bytes_unchecked(path),
+                )
+            }
+        }
+        None => (path, OsStr::new("")),
+    }
+}
+
+/// Returns a UTF-16 encoded path capable of bypassing the legacy `MAX_PATH` limits.
+///
+/// This path may or may not have a verbatim prefix.
+pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
+    let path = to_u16s(path)?;
+    get_long_path(path, true)
+}
+
+/// Get a normalized absolute path that can bypass path length limits.
+///
+/// Setting prefer_verbatim to true suggests a stronger preference for verbatim
+/// paths even when not strictly necessary. This allows the Windows API to avoid
+/// repeating our work. However, if the path may be given back to users or
+/// passed to other application then it's preferable to use non-verbatim paths
+/// when possible. Non-verbatim paths are better understood by users and handled
+/// by more software.
+pub(crate) fn get_long_path(mut path: Vec<u16>, prefer_verbatim: bool) -> io::Result<Vec<u16>> {
+    // Normally the MAX_PATH is 260 UTF-16 code units (including the NULL).
+    // However, for APIs such as CreateDirectory[1], the limit is 248.
+    //
+    // [1]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createdirectorya#parameters
+    const LEGACY_MAX_PATH: usize = 248;
+    // UTF-16 encoded code points, used in parsing and building UTF-16 paths.
+    // All of these are in the ASCII range so they can be cast directly to `u16`.
+    const SEP: u16 = b'\\' as _;
+    const ALT_SEP: u16 = b'/' as _;
+    const QUERY: u16 = b'?' as _;
+    const COLON: u16 = b':' as _;
+    const DOT: u16 = b'.' as _;
+    const U: u16 = b'U' as _;
+    const N: u16 = b'N' as _;
+    const C: u16 = b'C' as _;
+
+    // \\?\
+    const VERBATIM_PREFIX: &[u16] = &[SEP, SEP, QUERY, SEP];
+    // \??\
+    const NT_PREFIX: &[u16] = &[SEP, QUERY, QUERY, SEP];
+    // \\?\UNC\
+    const UNC_PREFIX: &[u16] = &[SEP, SEP, QUERY, SEP, U, N, C, SEP];
+
+    if path.starts_with(VERBATIM_PREFIX) || path.starts_with(NT_PREFIX) || path == [0] {
+        // Early return for paths that are already verbatim or empty.
+        return Ok(path);
+    } else if path.len() < LEGACY_MAX_PATH {
+        // Early return if an absolute path is less < 260 UTF-16 code units.
+        // This is an optimization to avoid calling `GetFullPathNameW` unnecessarily.
+        match path.as_slice() {
+            // Starts with `D:`, `D:\`, `D:/`, etc.
+            // Does not match if the path starts with a `\` or `/`.
+            [drive, COLON, 0] | [drive, COLON, SEP | ALT_SEP, ..]
+                if *drive != SEP && *drive != ALT_SEP =>
+            {
+                return Ok(path);
+            }
+            // Starts with `\\`, `//`, etc
+            [SEP | ALT_SEP, SEP | ALT_SEP, ..] => return Ok(path),
+            _ => {}
+        }
+    }
+
+    // Firstly, get the absolute path using `GetFullPathNameW`.
+    // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfullpathnamew
+    let lpfilename = path.as_ptr();
+    fill_utf16_buf(
+        // SAFETY: `fill_utf16_buf` ensures the `buffer` and `size` are valid.
+        // `lpfilename` is a pointer to a null terminated string that is not
+        // invalidated until after `GetFullPathNameW` returns successfully.
+        |buffer, size| unsafe { c::GetFullPathNameW(lpfilename, size, buffer, ptr::null_mut()) },
+        |mut absolute| {
+            path.clear();
+
+            // Only prepend the prefix if needed.
+            if prefer_verbatim || absolute.len() + 1 >= LEGACY_MAX_PATH {
+                // Secondly, add the verbatim prefix. This is easier here because we know the
+                // path is now absolute and fully normalized (e.g. `/` has been changed to `\`).
+                let prefix = match absolute {
+                    // C:\ => \\?\C:\
+                    [_, COLON, SEP, ..] => VERBATIM_PREFIX,
+                    // \\.\ => \\?\
+                    [SEP, SEP, DOT, SEP, ..] => {
+                        absolute = &absolute[4..];
+                        VERBATIM_PREFIX
+                    }
+                    // Leave \\?\ and \??\ as-is.
+                    [SEP, SEP, QUERY, SEP, ..] | [SEP, QUERY, QUERY, SEP, ..] => &[],
+                    // \\ => \\?\UNC\
+                    [SEP, SEP, ..] => {
+                        absolute = &absolute[2..];
+                        UNC_PREFIX
+                    }
+                    // Anything else we leave alone.
+                    _ => &[],
+                };
+
+                path.reserve_exact(prefix.len() + absolute.len() + 1);
+                path.extend_from_slice(prefix);
+            } else {
+                path.reserve_exact(absolute.len() + 1);
+            }
+            path.extend_from_slice(absolute);
+            path.push(0);
+        },
+    )?;
+    Ok(path)
+}
+
+/// Make a Windows path absolute.
+pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
+    let path = path.as_os_str();
+    let prefix = parse_prefix(path);
+    // Verbatim paths should not be modified.
+    if prefix.map(|x| x.is_verbatim()).unwrap_or(false) {
+        // NULs in verbatim paths are rejected for consistency.
+        if path.as_encoded_bytes().contains(&0) {
+            return Err(io::const_io_error!(
+                io::ErrorKind::InvalidInput,
+                "strings passed to WinAPI cannot contain NULs",
+            ));
+        }
+        return Ok(path.to_owned().into());
+    }
+
+    let path = to_u16s(path)?;
+    let lpfilename = path.as_ptr();
+    fill_utf16_buf(
+        // SAFETY: `fill_utf16_buf` ensures the `buffer` and `size` are valid.
+        // `lpfilename` is a pointer to a null terminated string that is not
+        // invalidated until after `GetFullPathNameW` returns successfully.
+        |buffer, size| unsafe { c::GetFullPathNameW(lpfilename, size, buffer, ptr::null_mut()) },
+        os2path,
+    )
+}
diff --git a/library/std/src/sys/path/windows/tests.rs b/library/std/src/sys/path/windows/tests.rs
new file mode 100644
index 00000000000..623c6236166
--- /dev/null
+++ b/library/std/src/sys/path/windows/tests.rs
@@ -0,0 +1,137 @@
+use super::*;
+
+#[test]
+fn test_parse_next_component() {
+    assert_eq!(
+        parse_next_component(OsStr::new(r"server\share"), true),
+        (OsStr::new(r"server"), OsStr::new(r"share"))
+    );
+
+    assert_eq!(
+        parse_next_component(OsStr::new(r"server/share"), true),
+        (OsStr::new(r"server/share"), OsStr::new(r""))
+    );
+
+    assert_eq!(
+        parse_next_component(OsStr::new(r"server/share"), false),
+        (OsStr::new(r"server"), OsStr::new(r"share"))
+    );
+
+    assert_eq!(
+        parse_next_component(OsStr::new(r"server\"), false),
+        (OsStr::new(r"server"), OsStr::new(r""))
+    );
+
+    assert_eq!(
+        parse_next_component(OsStr::new(r"\server\"), false),
+        (OsStr::new(r""), OsStr::new(r"server\"))
+    );
+
+    assert_eq!(
+        parse_next_component(OsStr::new(r"servershare"), false),
+        (OsStr::new(r"servershare"), OsStr::new(""))
+    );
+}
+
+#[test]
+fn verbatim() {
+    use crate::path::Path;
+    fn check(path: &str, expected: &str) {
+        let verbatim = maybe_verbatim(Path::new(path)).unwrap();
+        let verbatim = String::from_utf16_lossy(verbatim.strip_suffix(&[0]).unwrap());
+        assert_eq!(&verbatim, expected, "{}", path);
+    }
+
+    // Ensure long paths are correctly prefixed.
+    check(
+        r"C:\Program Files\Rust\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+        r"\\?\C:\Program Files\Rust\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+    );
+    check(
+        r"\\server\share\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+        r"\\?\UNC\server\share\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+    );
+    check(
+        r"\\.\PIPE\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+        r"\\?\PIPE\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+    );
+    // `\\?\` prefixed paths are left unchanged...
+    check(
+        r"\\?\verbatim.\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+        r"\\?\verbatim.\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+    );
+    // But `//?/` is not a verbatim prefix so it will be normalized.
+    check(
+        r"//?/E:/verbatim.\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+        r"\\?\E:\verbatim\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\foo.txt",
+    );
+
+    // For performance, short absolute paths are left unchanged.
+    check(r"C:\Program Files\Rust", r"C:\Program Files\Rust");
+    check(r"\\server\share", r"\\server\share");
+    check(r"\\.\COM1", r"\\.\COM1");
+
+    // Check that paths of length 247 are converted to verbatim.
+    // This is necessary for `CreateDirectory`.
+    check(
+        r"C:\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+        r"\\?\C:\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+    );
+
+    // Make sure opening a drive will work.
+    check("Z:", "Z:");
+
+    // A path that contains null is not a valid path.
+    assert!(maybe_verbatim(Path::new("\0")).is_err());
+}
+
+fn parse_prefix(path: &str) -> Option<Prefix<'_>> {
+    super::parse_prefix(OsStr::new(path))
+}
+
+#[test]
+fn test_parse_prefix_verbatim() {
+    let prefix = Some(Prefix::VerbatimDisk(b'C'));
+    assert_eq!(prefix, parse_prefix(r"\\?\C:/windows/system32/notepad.exe"));
+    assert_eq!(prefix, parse_prefix(r"\\?\C:\windows\system32\notepad.exe"));
+}
+
+#[test]
+fn test_parse_prefix_verbatim_device() {
+    let prefix = Some(Prefix::UNC(OsStr::new("?"), OsStr::new("C:")));
+    assert_eq!(prefix, parse_prefix(r"//?/C:/windows/system32/notepad.exe"));
+    assert_eq!(prefix, parse_prefix(r"//?/C:\windows\system32\notepad.exe"));
+    assert_eq!(prefix, parse_prefix(r"/\?\C:\windows\system32\notepad.exe"));
+    assert_eq!(prefix, parse_prefix(r"\\?/C:\windows\system32\notepad.exe"));
+}
+
+// See #93586 for more information.
+#[test]
+fn test_windows_prefix_components() {
+    use crate::path::Path;
+
+    let path = Path::new("C:");
+    let mut components = path.components();
+    let drive = components.next().expect("drive is expected here");
+    assert_eq!(drive.as_os_str(), OsStr::new("C:"));
+    assert_eq!(components.as_path(), Path::new(""));
+}
+
+/// See #101358.
+///
+/// Note that the exact behaviour here may change in the future.
+/// In which case this test will need to adjusted.
+#[test]
+fn broken_unc_path() {
+    use crate::path::Component;
+
+    let mut components = Path::new(r"\\foo\\bar\\").components();
+    assert_eq!(components.next(), Some(Component::RootDir));
+    assert_eq!(components.next(), Some(Component::Normal("foo".as_ref())));
+    assert_eq!(components.next(), Some(Component::Normal("bar".as_ref())));
+
+    let mut components = Path::new("//foo//bar//").components();
+    assert_eq!(components.next(), Some(Component::RootDir));
+    assert_eq!(components.next(), Some(Component::Normal("foo".as_ref())));
+    assert_eq!(components.next(), Some(Component::Normal("bar".as_ref())));
+}