gio: Fix segfault in ListStore::find_with_equal_func

Author: pjungkamp

gio/src/list_store.rs

@@ -150,14 +150,21 @@ impl ListStore {
             (*func)(&a).into_glib()
         }
 
+        // GIO prior to 2.76 requires a non-NULL item to be passed in so we're constructing a fake item here.
+        // See https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3284
+        #[cfg(not(feature = "v2_76"))]
         unsafe {
-            // GIO requires a non-NULL item to be passed in so we're constructing a fake item here.
-            // See https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3284
+            let g_class: *mut glib::gobject_ffi::GTypeClass =
+                glib::gobject_ffi::g_type_class_peek(self.item_type().into_glib()) as *mut _;
+
+            // g_class will be `NULL` when no instance of the `item-type` has been created yet.
+            // See https://github.com/gtk-rs/gtk-rs-core/issues/1767
+            if g_class.is_null() {
+                return None;
+            }
+
             let item = glib::gobject_ffi::GObject {
-                g_type_instance: glib::gobject_ffi::GTypeInstance {
-                    g_class: glib::gobject_ffi::g_type_class_peek(self.item_type().into_glib())
-                        as *mut _,
-                },
+                g_type_instance: glib::gobject_ffi::GTypeInstance { g_class },
                 ref_count: 1,
                 qdata: std::ptr::null_mut(),
             };
@@ -178,6 +185,26 @@ impl ListStore {
 
             found.then(|| position.assume_init())
         }
+
+        #[cfg(feature = "v2_76")]
+        unsafe {
+            let mut func = equal_func;
+            let func_obj: &mut (dyn FnMut(&Object) -> bool) = &mut func;
+            let func_ptr =
+                &func_obj as *const &mut (dyn FnMut(&Object) -> bool) as glib::ffi::gpointer;
+
+            let mut position = std::mem::MaybeUninit::uninit();
+
+            let found = bool::from_glib(ffi::g_list_store_find_with_equal_func_full(
+                self.to_glib_none().0,
+                std::ptr::null_mut(),
+                Some(equal_func_trampoline),
+                func_ptr,
+                position.as_mut_ptr(),
+            ));
+
+            found.then(|| position.assume_init())
+        }
     }
 }