Merge #5756

5756: Sophisticate Windows path encoding r=matklad a=pragmatrix

As discussed in #5475, path encoding should be agnostic of the drive letter casing on Windows.

Compared to the problem it solves, the code added seems a lot and may introduce other problems. But I've not found a simpler way basing this on the public API surface that Rust offers.

Fixes #5484.

cc @Emilgardis 

Co-authored-by: Armin Sander <armin@replicator.org>

crates/vfs/src/vfs_path.rs

@@ -57,30 +57,155 @@ impl VfsPath {
         };
         buf.push(tag);
         match &self.0 {
-            VfsPathRepr::PathBuf(it) => {
-                let path: &std::ffi::OsStr = it.as_os_str();
+            VfsPathRepr::PathBuf(path) => {
                 #[cfg(windows)]
                 {
-                    use std::os::windows::ffi::OsStrExt;
-                    for wchar in path.encode_wide() {
-                        buf.extend(wchar.to_le_bytes().iter().copied());
+                    use windows_paths::Encode;
+                    let components = path.components();
+                    let mut add_sep = false;
+                    for component in components {
+                        if add_sep {
+                            windows_paths::SEP.encode(buf);
+                        }
+                        let len_before = buf.len();
+                        match component {
+                            std::path::Component::Prefix(prefix) => {
+                                // kind() returns a normalized and comparable path prefix.
+                                prefix.kind().encode(buf);
+                            }
+                            std::path::Component::RootDir => {
+                                if !add_sep {
+                                    component.as_os_str().encode(buf);
+                                }
+                            }
+                            _ => component.as_os_str().encode(buf),
+                        }
+
+                        // some components may be encoded empty
+                        add_sep = len_before != buf.len();
                     }
                 }
                 #[cfg(unix)]
                 {
                     use std::os::unix::ffi::OsStrExt;
-                    buf.extend(path.as_bytes());
+                    buf.extend(path.as_os_str().as_bytes());
                 }
                 #[cfg(not(any(windows, unix)))]
                 {
-                    buf.extend(path.to_string_lossy().as_bytes());
+                    buf.extend(path.as_os_str().to_string_lossy().as_bytes());
                 }
             }
             VfsPathRepr::VirtualPath(VirtualPath(s)) => buf.extend(s.as_bytes()),
         }
     }
 }
 
+#[cfg(windows)]
+mod windows_paths {
+    pub trait Encode {
+        fn encode(&self, buf: &mut Vec<u8>);
+    }
+
+    impl Encode for std::ffi::OsStr {
+        fn encode(&self, buf: &mut Vec<u8>) {
+            use std::os::windows::ffi::OsStrExt;
+            for wchar in self.encode_wide() {
+                buf.extend(wchar.to_le_bytes().iter().copied());
+            }
+        }
+    }
+
+    impl Encode for u8 {
+        fn encode(&self, buf: &mut Vec<u8>) {
+            let wide = *self as u16;
+            buf.extend(wide.to_le_bytes().iter().copied())
+        }
+    }
+
+    impl Encode for &str {
+        fn encode(&self, buf: &mut Vec<u8>) {
+            debug_assert!(self.is_ascii());
+            for b in self.as_bytes() {
+                b.encode(buf)
+            }
+        }
+    }
+
+    pub const SEP: &str = "\\";
+    const VERBATIM: &str = "\\\\?\\";
+    const UNC: &str = "UNC";
+    const DEVICE: &str = "\\\\.\\";
+    const COLON: &str = ":";
+
+    impl Encode for std::path::Prefix<'_> {
+        fn encode(&self, buf: &mut Vec<u8>) {
+            match self {
+                std::path::Prefix::Verbatim(c) => {
+                    VERBATIM.encode(buf);
+                    c.encode(buf);
+                }
+                std::path::Prefix::VerbatimUNC(server, share) => {
+                    VERBATIM.encode(buf);
+                    UNC.encode(buf);
+                    SEP.encode(buf);
+                    server.encode(buf);
+                    SEP.encode(buf);
+                    share.encode(buf);
+                }
+                std::path::Prefix::VerbatimDisk(d) => {
+                    VERBATIM.encode(buf);
+                    d.encode(buf);
+                    COLON.encode(buf);
+                }
+                std::path::Prefix::DeviceNS(device) => {
+                    DEVICE.encode(buf);
+                    device.encode(buf);
+                }
+                std::path::Prefix::UNC(server, share) => {
+                    SEP.encode(buf);
+                    SEP.encode(buf);
+                    server.encode(buf);
+                    SEP.encode(buf);
+                    share.encode(buf);
+                }
+                std::path::Prefix::Disk(d) => {
+                    d.encode(buf);
+                    COLON.encode(buf);
+                }
+            }
+        }
+    }
+    #[test]
+    fn paths_encoding() {
+        // drive letter casing agnostic
+        test_eq("C:/x.rs", "c:/x.rs");
+        // separator agnostic
+        test_eq("C:/x/y.rs", "C:\\x\\y.rs");
+
+        fn test_eq(a: &str, b: &str) {
+            let mut b1 = Vec::new();
+            let mut b2 = Vec::new();
+            vfs(a).encode(&mut b1);
+            vfs(b).encode(&mut b2);
+            assert_eq!(b1, b2);
+        }
+    }
+
+    #[test]
+    fn test_sep_root_dir_encoding() {
+        let mut buf = Vec::new();
+        vfs("C:/x/y").encode(&mut buf);
+        assert_eq!(&buf, &[0, 67, 0, 58, 0, 92, 0, 120, 0, 92, 0, 121, 0])
+    }
+
+    #[cfg(test)]
+    fn vfs(str: &str) -> super::VfsPath {
+        use super::{AbsPathBuf, VfsPath};
+        use std::convert::TryFrom;
+        VfsPath::from(AbsPathBuf::try_from(str).unwrap())
+    }
+}
+
 #[derive(Clone, Ord, PartialOrd, Eq, PartialEq, Hash)]
 enum VfsPathRepr {
     PathBuf(AbsPathBuf),