Auto merge of #141864 - Berrysoft:cygwin-path, r=ChrisDenton

Handle win32 separator for cygwin paths

This PR handles a issue that cygwin actually supports Win32 path, so we need to handle the Win32 prefix and separaters.

r? `@mati865`

cc `@jeremyd2019`

~~Not sure if I should handle the prefix like the windows target... Cygwin *does* support win32 paths directly going through the APIs, but I think it's not the recommended way.~~

Here I just use `cygwin_conv_path` because it handles both cygwin and win32 paths correctly and convert them into absolute POSIX paths.

UPDATE: Windows path prefix is handled.

7 files changed, 772 insertions, 173 deletions

diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 0469db0814c..07f212b1135 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -1316,8 +1316,17 @@ impl PathBuf {
             need_sep = false
         }
 
+        let need_clear = if cfg!(target_os = "cygwin") {
+            // If path is absolute and its prefix is none, it is like `/foo`,
+            // and will be handled below.
+            path.prefix().is_some()
+        } else {
+            // On Unix: prefix is always None.
+            path.is_absolute() || path.prefix().is_some()
+        };
+
         // absolute `path` replaces `self`
-        if path.is_absolute() || path.prefix().is_some() {
+        if need_clear {
             self.inner.truncate(0);
 
         // verbatim paths need . and .. removed
@@ -3643,6 +3652,11 @@ impl Error for NormalizeError {}
 /// paths, this is currently equivalent to calling
 /// [`GetFullPathNameW`][windows-path].
 ///
+/// On Cygwin, this is currently equivalent to calling [`cygwin_conv_path`][cygwin-path]
+/// with mode `CCP_WIN_A_TO_POSIX`, and then being processed like other POSIX platforms.
+/// If a Windows path is given, it will be converted to an absolute POSIX path without
+/// keeping `..`.
+///
 /// Note that these [may change in the future][changes].
 ///
 /// # Errors
@@ -3700,6 +3714,7 @@ impl Error for NormalizeError {}
 /// [changes]: io#platform-specific-behavior
 /// [posix-semantics]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
 /// [windows-path]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfullpathnamew
+/// [cygwin-path]: https://cygwin.com/cygwin-api/func-cygwin-conv-path.html
 #[stable(feature = "absolute_path", since = "1.79.0")]
 pub fn absolute<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
     let path = path.as_ref();
diff --git a/library/std/src/sys/path/cygwin.rs b/library/std/src/sys/path/cygwin.rs
new file mode 100644
index 00000000000..e90372805bb
--- /dev/null
+++ b/library/std/src/sys/path/cygwin.rs
@@ -0,0 +1,92 @@
+use crate::ffi::OsString;
+use crate::os::unix::ffi::OsStringExt;
+use crate::path::{Path, PathBuf};
+use crate::sys::common::small_c_string::run_path_with_cstr;
+use crate::sys::cvt;
+use crate::{io, ptr};
+
+#[inline]
+pub fn is_sep_byte(b: u8) -> bool {
+    b == b'/' || b == b'\\'
+}
+
+/// Cygwin allways prefers `/` over `\`, and it always converts all `/` to `\`
+/// internally when calling Win32 APIs. Therefore, the server component of path
+/// `\\?\UNC\localhost/share` is `localhost/share` on Win32, but `localhost`
+/// on Cygwin.
+#[inline]
+pub fn is_verbatim_sep(b: u8) -> bool {
+    b == b'/' || b == b'\\'
+}
+
+pub use super::windows_prefix::parse_prefix;
+
+pub const MAIN_SEP_STR: &str = "/";
+pub const MAIN_SEP: char = '/';
+
+unsafe extern "C" {
+    // Doc: https://cygwin.com/cygwin-api/func-cygwin-conv-path.html
+    // Src: https://github.com/cygwin/cygwin/blob/718a15ba50e0d01c79800bd658c2477f9a603540/winsup/cygwin/path.cc#L3902
+    // Safety:
+    // * `what` should be `CCP_WIN_A_TO_POSIX` here
+    // * `from` is null-terminated UTF-8 path
+    // * `to` is buffer, the buffer size is `size`.
+    //
+    // Converts a path to an absolute POSIX path, no matter the input is Win32 path or POSIX path.
+    fn cygwin_conv_path(
+        what: libc::c_uint,
+        from: *const libc::c_char,
+        to: *mut u8,
+        size: libc::size_t,
+    ) -> libc::ssize_t;
+}
+
+const CCP_WIN_A_TO_POSIX: libc::c_uint = 2;
+
+/// Make a POSIX path absolute.
+pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
+    run_path_with_cstr(path, &|path| {
+        let conv = CCP_WIN_A_TO_POSIX;
+        let size = cvt(unsafe { cygwin_conv_path(conv, path.as_ptr(), ptr::null_mut(), 0) })?;
+        // If success, size should not be 0.
+        debug_assert!(size >= 1);
+        let size = size as usize;
+        let mut buffer = Vec::with_capacity(size);
+        cvt(unsafe { cygwin_conv_path(conv, path.as_ptr(), buffer.as_mut_ptr(), size) })?;
+        unsafe {
+            buffer.set_len(size - 1);
+        }
+        Ok(PathBuf::from(OsString::from_vec(buffer)))
+    })
+    .map(|path| {
+        if path.prefix().is_some() {
+            return path;
+        }
+
+        // From unix.rs
+        let mut components = path.components();
+        let path_os = path.as_os_str().as_encoded_bytes();
+
+        let mut normalized = if path_os.starts_with(b"//") && !path_os.starts_with(b"///") {
+            components.next();
+            PathBuf::from("//")
+        } else {
+            PathBuf::new()
+        };
+        normalized.extend(components);
+
+        if path_os.ends_with(b"/") {
+            normalized.push("");
+        }
+
+        normalized
+    })
+}
+
+pub(crate) fn is_absolute(path: &Path) -> bool {
+    if path.as_os_str().as_encoded_bytes().starts_with(b"\\") {
+        path.has_root() && path.prefix().is_some()
+    } else {
+        path.has_root()
+    }
+}
diff --git a/library/std/src/sys/path/mod.rs b/library/std/src/sys/path/mod.rs
index 1fa4e80d678..a4ff4338cf5 100644
--- a/library/std/src/sys/path/mod.rs
+++ b/library/std/src/sys/path/mod.rs
@@ -1,6 +1,7 @@
 cfg_if::cfg_if! {
     if #[cfg(target_os = "windows")] {
         mod windows;
+        mod windows_prefix;
         pub use windows::*;
     } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
         mod sgx;
@@ -11,6 +12,10 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_os = "uefi")] {
         mod uefi;
         pub use uefi::*;
+    } else if #[cfg(target_os = "cygwin")] {
+        mod cygwin;
+        mod windows_prefix;
+        pub use cygwin::*;
     } else {
         mod unix;
         pub use unix::*;
diff --git a/library/std/src/sys/path/windows.rs b/library/std/src/sys/path/windows.rs
index e0e003f6a81..f124e1e5a71 100644
--- a/library/std/src/sys/path/windows.rs
+++ b/library/std/src/sys/path/windows.rs
@@ -1,5 +1,5 @@
 use crate::ffi::{OsStr, OsString};
-use crate::path::{Path, PathBuf, Prefix};
+use crate::path::{Path, PathBuf};
 use crate::sys::api::utf16;
 use crate::sys::pal::{c, fill_utf16_buf, os2path, to_u16s};
 use crate::{io, ptr};
@@ -7,6 +7,8 @@ use crate::{io, ptr};
 #[cfg(test)]
 mod tests;
 
+pub use super::windows_prefix::parse_prefix;
+
 pub const MAIN_SEP_STR: &str = "\\";
 pub const MAIN_SEP: char = '\\';
 
@@ -77,177 +79,6 @@ pub(crate) fn append_suffix(path: PathBuf, suffix: &OsStr) -> PathBuf {
     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, UNC, Verbatim, VerbatimDisk, VerbatimUNC};
-
-    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.
diff --git a/library/std/src/sys/path/windows/tests.rs b/library/std/src/sys/path/windows/tests.rs
index 9eb79203dca..830f48d7bfc 100644
--- a/library/std/src/sys/path/windows/tests.rs
+++ b/library/std/src/sys/path/windows/tests.rs
@@ -1,4 +1,6 @@
+use super::super::windows_prefix::*;
 use super::*;
+use crate::path::Prefix;
 
 #[test]
 fn test_parse_next_component() {
diff --git a/library/std/src/sys/path/windows_prefix.rs b/library/std/src/sys/path/windows_prefix.rs
new file mode 100644
index 00000000000..b9dfe754485
--- /dev/null
+++ b/library/std/src/sys/path/windows_prefix.rs
@@ -0,0 +1,182 @@
+//! Parse Windows prefixes, for both Windows and Cygwin.
+
+use super::{is_sep_byte, is_verbatim_sep};
+use crate::ffi::OsStr;
+use crate::path::Prefix;
+
+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, UNC, Verbatim, VerbatimDisk, VerbatimUNC};
+
+    let parser = PrefixParser::<8>::new(path);
+    let parser = parser.as_slice();
+    if let Some(parser) = parser.strip_prefix(r"\\") {
+        // \\
+
+        // It's a POSIX path.
+        if cfg!(target_os = "cygwin") && !path.as_encoded_bytes().iter().any(|&x| x == b'\\') {
+            return None;
+        }
+
+        // The meaning of verbatim paths can change when they use a different
+        // separator.
+        if let Some(parser) = parser.strip_prefix(r"?\")
+            // Cygwin allows `/` in verbatim paths.
+            && (cfg!(target_os = "cygwin") || !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.
+        Some(Disk(parse_drive(path)?))
+    }
+}
+
+// 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 on Windows if `verbatim` is true.
+pub(crate) 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("")),
+    }
+}
diff --git a/library/std/tests/path.rs b/library/std/tests/path.rs
index be0dda1d426..901d2770f20 100644
--- a/library/std/tests/path.rs
+++ b/library/std/tests/path.rs
@@ -1112,6 +1112,473 @@ pub fn test_decompositions_windows() {
     );
 }
 
+// Unix paths are tested in `test_decompositions_unix` above.
+#[test]
+#[cfg(target_os = "cygwin")]
+pub fn test_decompositions_cygwin() {
+    t!("\\",
+    iter: ["/"],
+    has_root: true,
+    is_absolute: false,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("c:",
+    iter: ["c:"],
+    has_root: false,
+    is_absolute: false,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("c:\\",
+    iter: ["c:", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("c:/",
+    iter: ["c:", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("a\\b\\c",
+    iter: ["a", "b", "c"],
+    has_root: false,
+    is_absolute: false,
+    parent: Some("a\\b"),
+    file_name: Some("c"),
+    file_stem: Some("c"),
+    extension: None,
+    file_prefix: Some("c")
+    );
+
+    t!("\\a",
+    iter: ["/", "a"],
+    has_root: true,
+    is_absolute: false,
+    parent: Some("\\"),
+    file_name: Some("a"),
+    file_stem: Some("a"),
+    extension: None,
+    file_prefix: Some("a")
+    );
+
+    t!("c:\\foo.txt",
+    iter: ["c:", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("c:\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\server\\share\\foo.txt",
+    iter: ["\\\\server\\share", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\server\\share\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//server/share\\foo.txt",
+    iter: ["//server/share", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//server/share\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//server/share/foo.txt",
+    iter: ["/", "server", "share", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//server/share"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\server\\share",
+    iter: ["\\\\server\\share", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\server",
+    iter: ["/", "server"],
+    has_root: true,
+    is_absolute: false,
+    parent: Some("\\"),
+    file_name: Some("server"),
+    file_stem: Some("server"),
+    extension: None,
+    file_prefix: Some("server")
+    );
+
+    t!("\\\\?\\bar\\foo.txt",
+    iter: ["\\\\?\\bar", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\bar\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\?\\bar",
+    iter: ["\\\\?\\bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\",
+    iter: ["\\\\?\\"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\UNC\\server\\share\\foo.txt",
+    iter: ["\\\\?\\UNC\\server\\share", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\UNC\\server\\share\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\?\\UNC\\server/share\\foo.txt",
+    iter: ["\\\\?\\UNC\\server/share", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\UNC\\server/share\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//?/UNC/server\\share/foo.txt",
+    iter: ["//?/UNC/server\\share", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//?/UNC/server\\share/"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//?/UNC/server/share/foo.txt",
+    iter: ["/", "?", "UNC", "server", "share", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//?/UNC/server/share"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\?\\UNC\\server",
+    iter: ["\\\\?\\UNC\\server"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\UNC\\",
+    iter: ["\\\\?\\UNC\\"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\C:\\foo.txt",
+    iter: ["\\\\?\\C:", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\C:\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//?/C:\\foo.txt",
+    iter: ["//?/C:", "/", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//?/C:\\"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("//?/C:/foo.txt",
+    iter: ["/", "?", "C:", "foo.txt"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//?/C:"),
+    file_name: Some("foo.txt"),
+    file_stem: Some("foo"),
+    extension: Some("txt"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\?\\C:\\",
+    iter: ["\\\\?\\C:", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\C:",
+    iter: ["\\\\?\\C:"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\?\\foo/bar",
+    iter: ["\\\\?\\foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\foo/"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\?\\C:/foo/bar",
+    iter: ["\\\\?\\C:", "/", "foo", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\C:/foo"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\.\\foo\\bar",
+    iter: ["\\\\.\\foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\.\\foo\\"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\.\\foo",
+    iter: ["\\\\.\\foo", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("\\\\.\\foo/bar",
+    iter: ["\\\\.\\foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\.\\foo/"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\.\\foo\\bar/baz",
+    iter: ["\\\\.\\foo", "/", "bar", "baz"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\.\\foo\\bar"),
+    file_name: Some("baz"),
+    file_stem: Some("baz"),
+    extension: None,
+    file_prefix: Some("baz")
+    );
+
+    t!("\\\\.\\",
+    iter: ["\\\\.\\", "/"],
+    has_root: true,
+    is_absolute: true,
+    parent: None,
+    file_name: None,
+    file_stem: None,
+    extension: None,
+    file_prefix: None
+    );
+
+    t!("//.\\foo/bar",
+    iter: ["//.\\foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//.\\foo/"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\./foo/bar",
+    iter: ["\\\\./foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\./foo/"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("//./foo\\bar",
+    iter: ["//./foo", "/", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//./foo\\"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("//./?/C:/foo/bar",
+    iter: ["/", "?", "C:", "foo", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//./?/C:/foo"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("//././../././../?/C:/foo/bar",
+    iter: ["/", "..", "..", "?", "C:", "foo", "bar"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("//././../././../?/C:/foo"),
+    file_name: Some("bar"),
+    file_stem: Some("bar"),
+    extension: None,
+    file_prefix: Some("bar")
+    );
+
+    t!("\\\\?\\a\\b\\",
+    iter: ["\\\\?\\a", "/", "b"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\a\\"),
+    file_name: Some("b"),
+    file_stem: Some("b"),
+    extension: None,
+    file_prefix: Some("b")
+    );
+
+    t!("\\\\?\\C:\\foo.txt.zip",
+    iter: ["\\\\?\\C:", "/", "foo.txt.zip"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\C:\\"),
+    file_name: Some("foo.txt.zip"),
+    file_stem: Some("foo.txt"),
+    extension: Some("zip"),
+    file_prefix: Some("foo")
+    );
+
+    t!("\\\\?\\C:\\.foo.txt.zip",
+    iter: ["\\\\?\\C:", "/", ".foo.txt.zip"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\C:\\"),
+    file_name: Some(".foo.txt.zip"),
+    file_stem: Some(".foo.txt"),
+    extension: Some("zip"),
+    file_prefix: Some(".foo")
+    );
+
+    t!("\\\\?\\C:\\.foo",
+    iter: ["\\\\?\\C:", "/", ".foo"],
+    has_root: true,
+    is_absolute: true,
+    parent: Some("\\\\?\\C:\\"),
+    file_name: Some(".foo"),
+    file_stem: Some(".foo"),
+    extension: None,
+    file_prefix: Some(".foo")
+    );
+}
+
 #[test]
 pub fn test_stem_ext() {
     t!("foo",
@@ -1227,6 +1694,11 @@ pub fn test_push() {
         tp!("/foo/bar", "/", "/");
         tp!("/foo/bar", "/baz", "/baz");
         tp!("/foo/bar", "./baz", "/foo/bar/./baz");
+
+        if cfg!(target_os = "cygwin") {
+            tp!("c:\\", "windows", "c:\\windows");
+            tp!("c:", "windows", "c:windows");
+        }
     } else {
         tp!("", "foo", "foo");
         tp!("foo", "bar", r"foo\bar");