+
+// On Windows the compiler would sometimes intermittently fail to open the
+// proc-macro DLL with `Error::LoadLibraryExW`. It is suspected that something in the
+// system still holds a lock on the file, so we retry a few times before calling it
+// an error.
+fn load_dylib(path: &Path, max_attempts: usize) -> Result<libloading::Library, String> {
+ assert!(max_attempts > 0);
+
+ let mut last_error = None;
+
+ for attempt in 0..max_attempts {
+ match unsafe { libloading::Library::new(&path) } {
+ Ok(lib) => {
+ if attempt > 0 {
+ debug!(
+ "Loaded proc-macro `{}` after {} attempts.",
+ path.display(),
+ attempt + 1
+ );
+ }
+ return Ok(lib);
+ }
+ Err(err) => {
+ // Only try to recover from this specific error.
+ if !matches!(err, libloading::Error::LoadLibraryExW { .. }) {
+ return Err(err.to_string());
+ }
+
+ last_error = Some(err);
+ std::thread::sleep(Duration::from_millis(100));
+ debug!("Failed to load proc-macro `{}`. Retrying.", path.display());
+ }
+ }
+ }
+
+ debug!("Failed to load proc-macro `{}` even after {} attempts.", path.display(), max_attempts);
+ Err(format!("{} (retried {} times)", last_error.unwrap(), max_attempts))
+}