Don't allow trivial UB via FieldSlot in safe code

cf. https://x.com/qdoit_/status/1848004580115726710, thanks qdoit_ and kupiakos on twitter!
bearcove · Oct 20, 2024 · b307ad6 · b307ad6
1 parent 22be5ed
commit b307ad6
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Showing 2 changed files with 5 additions and 6 deletions.
diff --git a/merde/src/lib.rs b/merde/src/lib.rs
@@ -100,8 +100,7 @@ macro_rules! impl_deserialize {
                 Ok($struct_name {
                     $($field: {
                         if $field.is_none() {
-                            let __field_type_name = std::any::type_name_of_val(&$field);
-                            let __slot = $crate::FieldSlot::new(&mut $field, __field_type_name);
+                            let __slot = $crate::FieldSlot::new(&mut $field);
                             __opinions.default_field_value(stringify!($field), __slot);
                         }
                         $crate::Deserialize::from_option($field, stringify!($field).into())?
@@ -163,8 +162,7 @@ macro_rules! impl_deserialize {
                 Ok($struct_name {
                     $($field: {
                         if $field.is_none() {
-                            let __field_type_name = std::any::type_name_of_val(&$field);
-                            let __slot = $crate::FieldSlot::new(&mut $field, __field_type_name);
+                            let __slot = $crate::FieldSlot::new(&mut $field);
                             __opinions.default_field_value(stringify!($field), __slot);
                         }
                         $crate::Deserialize::from_option($field, stringify!($field).into())?

diff --git a/merde_core/src/deserialize.rs b/merde_core/src/deserialize.rs
@@ -317,12 +317,13 @@ pub struct FieldSlot<'s, 'borrow> {
 impl<'s, 'borrow> FieldSlot<'s, 'borrow> {
     /// Construct a new `FieldSlot`, ready to be filled
     #[inline(always)]
-    pub fn new<T: 's>(option: &'borrow mut Option<T>, type_name_of_slot: &'static str) -> Self {
+    #[doc(hidden)]
+    pub fn new<T: 's>(option: &'borrow mut Option<T>) -> Self {
         Self {
             option: unsafe {
                 std::mem::transmute::<*mut Option<T>, *mut Option<()>>(option as *mut _)
             },
-            type_name_of_option_field: type_name_of_slot,
+            type_name_of_option_field: std::any::type_name::<Option<T>>(),
             _phantom: PhantomData,
         }
     }