Merge pull request #3616 from neachdainn/3615-gilprotected-pyvisit

Enable `GILProtected` access via `PyVisit`

newsfragments/3616.added.md

@@ -0,0 +1 @@
+Add `traverse` method to `GILProtected`

src/sync.rs

@@ -1,5 +1,5 @@
 //! Synchronization mechanisms based on the Python GIL.
-use crate::{types::PyString, types::PyType, Py, PyErr, Python};
+use crate::{types::PyString, types::PyType, Py, PyErr, PyVisit, Python};
 use std::cell::UnsafeCell;
 
 /// Value with concurrent access protected by the GIL.
@@ -37,6 +37,11 @@ impl<T> GILProtected<T> {
     pub fn get<'py>(&'py self, _py: Python<'py>) -> &'py T {
         &self.value
     }
+
+    /// Gain access to the inner value by giving proof that garbage collection is happening.
+    pub fn traverse<'py>(&'py self, _visit: PyVisit<'py>) -> &'py T {
+        &self.value
+    }
 }
 
 unsafe impl<T> Sync for GILProtected<T> where T: Send {}