let fields = &def_a.non_enum_variant().fields;
let coerced_fields = fields.iter().filter_map(|field| {
- if tcx.type_of(field.did).is_phantom_data() {
- // ignore PhantomData fields
- return None
- }
-
let ty_a = field.ty(tcx, substs_a);
let ty_b = field.ty(tcx, substs_b);
+
+ if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) {
+ if layout.is_zst() {
+ // ignore ZST fields
+ return None;
+ }
+ }
+
if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) {
if ok.obligations.is_empty() {
create_err(
"the trait `DispatchFromDyn` may only be implemented \
for structs containing the field being coerced, \
- `PhantomData` fields, and nothing else"
+ ZST fields, and nothing else"
).note(
&format!(
"extra field `{}` of type `{}` is not allowed",
--- /dev/null
+#![feature(unsize, dispatch_from_dyn, never_type)]
+
+#![allow(dead_code)]
+
+use std::{
+ ops::DispatchFromDyn,
+ marker::{Unsize, PhantomData},
+};
+
+struct Zst;
+struct NestedZst(PhantomData<()>, Zst);
+
+
+struct WithUnit<T: ?Sized>(Box<T>, ());
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithUnit<U>> for WithUnit<T>
+ where T: Unsize<U> {}
+
+struct WithPhantom<T: ?Sized>(Box<T>, PhantomData<()>);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithPhantom<U>> for WithPhantom<T>
+ where T: Unsize<U> {}
+
+struct WithNever<T: ?Sized>(Box<T>, !);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithNever<U>> for WithNever<T>
+ where T: Unsize<U> {}
+
+struct WithZst<T: ?Sized>(Box<T>, Zst);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithZst<U>> for WithZst<T>
+ where T: Unsize<U> {}
+
+struct WithNestedZst<T: ?Sized>(Box<T>, NestedZst);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithNestedZst<U>> for WithNestedZst<T>
+ where T: Unsize<U> {}
+
+
+struct Generic<T: ?Sized, A>(Box<T>, A);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, ()>> for Generic<T, ()>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, PhantomData<()>>>
+ for Generic<T, PhantomData<()>>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, !>> for Generic<T, !>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, Zst>> for Generic<T, Zst>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, NestedZst>> for Generic<T, NestedZst>
+ where T: Unsize<U> {}
+
+
+fn main() {}
-error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, `PhantomData` fields, and nothing else
+error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields, and nothing else
--> $DIR/invalid_dispatch_from_dyn_impls.rs:10:1
|
LL | / impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>