Fix UB, the value in MaybeUninit was being dropped

examples/gauge.rs

@@ -74,6 +74,8 @@ fn main() -> Result<(), LvError> {
 
     let mut i = 0;
     'running: loop {
+        gauge.set_value(0, i)?;
+
         let mut ui = threaded_ui.lock().unwrap();
         ui.task_handler();
         if let Some(disp) = ui.get_display_ref() {
@@ -93,8 +95,7 @@ fn main() -> Result<(), LvError> {
             }
         }
 
-        sleep(Duration::from_millis(25));
+        sleep(Duration::from_millis(50));
-        gauge.set_value(0, i)?;
 
         if i > 99 {
             i = 0;

lvgl/src/mem.rs

@@ -1,5 +1,6 @@
 use crate::{LvError, LvResult};
 use core::mem;
+use core::ops::{Deref, DerefMut};
 use core::ptr::NonNull;
 
 /// Places `T` into LVGL memory.
@@ -45,6 +46,20 @@ impl<T> Drop for Box<T> {
     }
 }
 
+impl<T> DerefMut for Box<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.as_mut()
+    }
+}
+
+impl<T> Deref for Box<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        unsafe { self.0.as_ref() }
+    }
+}
+
 impl<T> AsMut<T> for Box<T> {
     fn as_mut(&mut self) -> &mut T {
         unsafe { self.0.as_mut() }

lvgl/src/ui.rs

@@ -1,7 +1,7 @@
 use crate::mem::Box;
 use crate::{Color, Event, LvError, LvResult, Obj, Widget};
 use core::marker::PhantomData;
-use core::mem::{ManuallyDrop, MaybeUninit};
+use core::mem::MaybeUninit;
 use core::ptr;
 use core::ptr::NonNull;
 use core::sync::atomic::{AtomicBool, Ordering};
@@ -81,15 +81,13 @@ where
             let mut disp_drv = MaybeUninit::<lvgl_sys::lv_disp_drv_t>::uninit();
             lvgl_sys::lv_disp_drv_init(disp_drv.as_mut_ptr());
             // Since this is C managed memory, we don't want to drop it using Rust, thus `ManuallyDrop` wrapping.
-            let mut disp_drv = ManuallyDrop::new(disp_drv.assume_init());
+            let mut disp_drv = Box::new(disp_drv.assume_init())?;
             // Assign the buffer to the display
             disp_drv.buffer = Box::into_raw(disp_buf);
             // Set your driver function
             disp_drv.flush_cb = Some(display_callback_wrapper::<T, C>);
             disp_drv.user_data = &mut self.display_data as *mut _ as *mut cty::c_void;
-            lvgl_sys::lv_disp_drv_register(
+            lvgl_sys::lv_disp_drv_register(Box::into_raw(disp_drv));
-                &mut ManuallyDrop::take(&mut disp_drv) as *mut lvgl_sys::lv_disp_drv_t
-            );
         };
 
         Ok(())