Fix AppExit panic.

Author: tychedelia

crates/processing_core/src/lib.rs

@@ -14,14 +14,21 @@ thread_local! {
 }
 
 pub fn app_mut<T>(cb: impl FnOnce(&mut App) -> error::Result<T>) -> error::Result<T> {
-    let res = APP.with(|app_cell| {
-        let mut app_borrow = app_cell.borrow_mut();
+    // `try_with` so a `Drop` running after the TLS is destroyed sees an
+    // `AppAccess` error rather than panicking
+    let res = APP.try_with(|app_cell| {
+        let mut app_borrow = app_cell
+            .try_borrow_mut()
+            .map_err(|_| error::ProcessingError::AppAccess)?;
         let app = app_borrow
             .as_mut()
             .ok_or(error::ProcessingError::AppAccess)?;
         cb(app)
-    })?;
-    Ok(res)
+    });
+    match res {
+        Ok(inner) => inner,
+        Err(_) => Err(error::ProcessingError::AppAccess),
+    }
 }
 
 pub fn is_already_init() -> error::Result<bool> {

crates/processing_pyo3/src/lib.rs

@@ -1017,7 +1017,7 @@ mod mewnala {
             return Ok(());
         }
 
-        Python::attach(|py| {
+        let result: PyResult<()> = Python::attach(|py| {
             let builtins = PyModule::import(py, "builtins")?;
             let locals = builtins.getattr("locals")?.call0()?;
 
@@ -1138,7 +1138,13 @@ mod mewnala {
             }
 
             Ok(())
-        })
+        });
+
+        // tear the app down here while the TLS is still alive; the eager
+        // TLS destructor aborts inside a Bevy resource drop
+        let _ = ::processing::exit(0);
+
+        result
     }
 
     #[pyfunction]