1 files changed, 92 insertions, 0 deletions
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()
+    }
+}