Self review, update pymetabind, resolve TODO

Author: oremanj

include/pybind11/cast.h

@@ -876,20 +876,20 @@ struct holder_caster_foreign_helpers {
         PyObject *o;
     };
 
-    template <typename type>
-    static bool try_shared_from_this(std::enable_shared_from_this<type> *value,
+    template <typename base, typename type>
+    static bool try_shared_from_this(std::enable_shared_from_this<base> *value,
                                      std::shared_ptr<type> *holder_out) {
         // object derives from enable_shared_from_this;
         // try to reuse an existing shared_ptr if one is known
         if (auto existing = try_get_shared_from_this(value)) {
-            *holder_out = existing;
+            *holder_out = std::static_pointer_cast<type>(existing);
             return true;
         }
         return false;
     }
 
     template <typename type>
-    static bool try_shared_from_this(type *, std::shared_ptr<type> *) {
+    static bool try_shared_from_this(void *, std::shared_ptr<type> *) {
         return false;
     }
 

include/pybind11/detail/foreign.h

@@ -289,10 +289,8 @@ PYBIND11_NOINLINE bool foreign_internals::initialize() {
 
         self.reset(new pymb_framework{});
         self->name = "pybind11 " PYBIND11_ABI_TAG;
-        // TODO: pybind11 does leak some bindings; there should be a way to
-        // indicate that (so that eg nanobind can disable its leak detection)
-        // without promising to leak all bindings
         self->bindings_usable_forever = 0;
+        self->leak_safe = 0;
         self->abi_lang = pymb_abi_lang_cpp;
         self->abi_extra = PYBIND11_PLATFORM_ABI_ID;
         self->from_python = foreign_cb_from_python;

include/pybind11/detail/pymetabind.h

@@ -6,7 +6,10 @@
  * This functionality is intended to be used by the framework itself,
  * rather than by users of the framework.
  *
- * This is version 0.1 of pymetabind. Changelog:
+ * This is version 0.1+dev of pymetabind. Changelog:
+ *
+ *      Unreleased: Fix typo in Py_GIL_DISABLED. Add pymb_framework::leak_safe.
+ *                  Add casts from PyTypeObject* to PyObject* where needed.
  *
  *     Version 0.1: Initial draft. ABI may change without warning while we
  *      2025-08-16  prove out the concept. Please wait for a 1.0 release
@@ -195,7 +198,7 @@ struct pymb_registry {
 #endif
 };
 
-#if defined(Py_GIL_DISALED)
+#if defined(Py_GIL_DISABLED)
 inline void pymb_lock_registry(struct pymb_registry* registry) {
     PyMutex_Lock(&registry->mutex);
 }
@@ -250,8 +253,15 @@ struct pymb_framework {
     // this framework's bindings in free-threaded builds.
     uint8_t bindings_usable_forever;
 
+    // Does this framework reliably deallocate all of its type and function
+    // objects by the time the Python interpreter is finalized, in the absence
+    // of bugs in user code? If not, it might cause leaks of other frameworks'
+    // types or functions, via attributes or default argument values for
+    // this framework's leaked objects.
+    uint8_t leak_safe;
+
     // Reserved for future extensions. Set to 0.
-    uint8_t reserved[3];
+    uint8_t reserved[2];
 
     // The language to which this framework provides bindings: one of the
     // `pymb_abi_lang` enumerators.