Make sure CreateDirectoryW works for path lengths > 247

library/std/src/fs/tests.rs

@@ -1411,3 +1411,32 @@ fn symlink_hard_link() {
     // "hard_link" should still appear as a symlink.
     assert!(check!(fs::symlink_metadata(tmpdir.join("hard_link"))).file_type().is_symlink());
 }
+
+/// Ensure `fs::create_dir` works on Windows with longer paths.
+#[test]
+#[cfg(windows)]
+fn create_dir_long_paths() {
+    use crate::{ffi::OsStr, iter, os::windows::ffi::OsStrExt};
+    const PATH_LEN: usize = 247;
+
+    let tmpdir = tmpdir();
+    let mut path = tmpdir.path().to_path_buf();
+    path.push("a");
+    let mut path = path.into_os_string();
+
+    let utf16_len = path.encode_wide().count();
+    if utf16_len >= PATH_LEN {
+        // Skip the test in the unlikely event the local user has a long temp directory path.
+        // This should not affect CI.
+        return;
+    }
+    // Increase the length of the path.
+    path.extend(iter::repeat(OsStr::new("a")).take(PATH_LEN - utf16_len));
+
+    // This should succeed.
+    fs::create_dir(&path).unwrap();
+
+    // This will fail if the path isn't converted to verbatim.
+    path.push("a");
+    fs::create_dir(&path).unwrap();
+}