check for correct trait in size_and_align_of

Author: RalfJung

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -765,10 +765,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 }
                 Ok(Some((full_size, full_align)))
             }
-            ty::Dynamic(_, _, ty::Dyn) => {
+            ty::Dynamic(expected_trait, _, ty::Dyn) => {
                 let vtable = metadata.unwrap_meta().to_pointer(self)?;
                 // Read size and align from vtable (already checks size).
-                Ok(Some(self.get_vtable_size_and_align(vtable)?))
+                Ok(Some(self.get_vtable_size_and_align(vtable, Some(expected_trait))?))
             }
 
             ty::Slice(_) | ty::Str => {

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -432,12 +432,14 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
             sym::vtable_size => {
                 let ptr = self.read_pointer(&args[0])?;
-                let (size, _align) = self.get_vtable_size_and_align(ptr)?;
+                // `None` because we don't know which trait to expect here; any vtable is okay.
+                let (size, _align) = self.get_vtable_size_and_align(ptr, None)?;
                 self.write_scalar(Scalar::from_target_usize(size.bytes(), self), dest)?;
             }
             sym::vtable_align => {
                 let ptr = self.read_pointer(&args[0])?;
-                let (_size, align) = self.get_vtable_size_and_align(ptr)?;
+                // `None` because we don't know which trait to expect here; any vtable is okay.
+                let (_size, align) = self.get_vtable_size_and_align(ptr, None)?;
                 self.write_scalar(Scalar::from_target_usize(align.bytes(), self), dest)?;
             }
 

compiler/rustc_const_eval/src/interpret/traits.rs

@@ -36,8 +36,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     pub fn get_vtable_size_and_align(
         &self,
         vtable: Pointer<Option<M::Provenance>>,
+        expected_trait: Option<&'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>>,
     ) -> InterpResult<'tcx, (Size, Align)> {
-        let ty = self.get_ptr_vtable_ty(vtable, None)?;
+        let ty = self.get_ptr_vtable_ty(vtable, expected_trait)?;
         let layout = self.layout_of(ty)?;
         assert!(layout.is_sized(), "there are no vtables for unsized types");
         Ok((layout.size, layout.align.abi))