Refactor Capable::vtable to return Option<NonNull<()>> (#4252)

crates/typst-macros/src/elem.rs

@@ -845,7 +845,7 @@ fn create_capable_impl(element: &Elem) -> TokenStream {
 
     quote! {
         unsafe impl #foundations::Capable for #ident {
-            fn vtable(capability: ::std::any::TypeId) -> ::std::option::Option<*const ()> {
+            fn vtable(capability: ::std::any::TypeId) -> ::std::option::Option<::std::ptr::NonNull<()>> {
                 let dangling = ::std::ptr::NonNull::<#foundations::Packed<#ident>>::dangling().as_ptr();
                 #(#checks)*
                 None

crates/typst-utils/src/fat.rs

@@ -7,6 +7,7 @@
 
 use std::alloc::Layout;
 use std::mem;
+use std::ptr::NonNull;
 
 /// Create a fat pointer from a data address and a vtable address.
 ///
@@ -39,9 +40,11 @@ pub unsafe fn from_raw_parts_mut<T: ?Sized>(data: *mut (), vtable: *const ()) ->
 /// # Safety
 /// Must only be called when `T` is a `dyn Trait`.
 #[track_caller]
-pub unsafe fn vtable<T: ?Sized>(ptr: *const T) -> *const () {
+pub unsafe fn vtable<T: ?Sized>(ptr: *const T) -> NonNull<()> {
     debug_assert_eq!(Layout::new::<*const T>(), Layout::new::<FatPointer>());
-    mem::transmute_copy::<*const T, FatPointer>(&ptr).vtable
+    NonNull::new_unchecked(
+        mem::transmute_copy::<*const T, FatPointer>(&ptr).vtable as *mut (),
+    )
 }
 
 /// The memory representation of a trait object pointer.

crates/typst/src/foundations/content.rs

@@ -299,7 +299,7 @@ impl Content {
         // use a `*const Content` pointer.
         let vtable = self.elem().vtable()(TypeId::of::<C>())?;
         let data = self as *const Content as *const ();
-        Some(unsafe { &*fat::from_raw_parts(data, vtable) })
+        Some(unsafe { &*fat::from_raw_parts(data, vtable.as_ptr()) })
     }
 
     /// Cast to a mutable trait object if the contained element has the given
@@ -319,7 +319,7 @@ impl Content {
         // mutable access is required.
         let vtable = self.elem().vtable()(TypeId::of::<C>())?;
         let data = self as *mut Content as *mut ();
-        Some(unsafe { &mut *fat::from_raw_parts_mut(data, vtable) })
+        Some(unsafe { &mut *fat::from_raw_parts_mut(data, vtable.as_ptr()) })
     }
 
     /// Whether the content is an empty sequence.

crates/typst/src/foundations/element.rs

@@ -2,6 +2,7 @@ use std::any::TypeId;
 use std::cmp::Ordering;
 use std::fmt::{self, Debug};
 use std::hash::Hash;
+use std::ptr::NonNull;
 
 use ecow::EcoString;
 use once_cell::sync::Lazy;
@@ -81,7 +82,7 @@ impl Element {
     }
 
     /// The VTable for capabilities dispatch.
-    pub fn vtable(self) -> fn(of: TypeId) -> Option<*const ()> {
+    pub fn vtable(self) -> fn(of: TypeId) -> Option<NonNull<()>> {
         self.0.vtable
     }
 
@@ -208,7 +209,7 @@ pub trait NativeElement:
 /// `TypeId::of::<dyn C>()`.
 pub unsafe trait Capable {
     /// Get the pointer to the vtable for the given capability / trait.
-    fn vtable(capability: TypeId) -> Option<*const ()>;
+    fn vtable(capability: TypeId) -> Option<NonNull<()>>;
 }
 
 /// Defines how fields of an element are accessed.
@@ -275,7 +276,7 @@ pub struct NativeElementData {
     pub set: fn(&mut Engine, &mut Args) -> SourceResult<Styles>,
     /// Gets the vtable for one of this element's capabilities
     /// (see [`Capable`]).
-    pub vtable: fn(capability: TypeId) -> Option<*const ()>,
+    pub vtable: fn(capability: TypeId) -> Option<NonNull<()>>,
     /// Gets the numeric index of this field by its name.
     pub field_id: fn(name: &str) -> Option<u8>,
     /// Gets the name of a field by its numeric index.