Auto merge of rust-lang#116606 - ChrisDenton:empty, r=dtolnay

On Windows make `read_dir` error on the empty path

This makes Windows consistent with other platforms. Note that this should not be taken to imply any decision on rust-lang#114149 has been taken. However it was felt that while there is a lack of libs-api consensus, we should be consistent across platforms in the meantime.

This is a change in behaviour for Windows so will also need an fcp before merging.

r? libs-api

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

@@ -1066,6 +1066,14 @@ impl DirBuilder {
 }
 
 pub fn readdir(p: &Path) -> io::Result<ReadDir> {
+    // We push a `*` to the end of the path which cause the empty path to be
+    // treated as the current directory. So, for consistency with other platforms,
+    // we explicitly error on the empty path.
+    if p.as_os_str().is_empty() {
+        // Return an error code consistent with other ways of opening files.
+        // E.g. fs::metadata or File::open.
+        return Err(io::Error::from_raw_os_error(c::ERROR_PATH_NOT_FOUND as i32));
+    }
     let root = p.to_path_buf();
     let star = p.join("*");
     let path = maybe_verbatim(&star)?;