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Only allow ZSTs with 1 byte alignment

This commit is contained in:
Tim Diekmann 2019-04-30 14:38:17 +02:00
parent abf73a6aeb
commit 1b679e74f0
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GPG Key ID: 58CD76F88DF563E0
3 changed files with 25 additions and 5 deletions
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6
src/librustc_typeck/coherence/builtin.rs
View File

@ -227,8 +227,8 @@ fn visit_implementation_of_dispatch_from_dyn<'a, 'tcx>(
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
if layout.is_zst() && layout.details.align.abi.bytes() == 1 {
// ignore ZST fields with alignment of 1 byte
return None;
}
}
@ -238,7 +238,7 @@ fn visit_implementation_of_dispatch_from_dyn<'a, 'tcx>(
create_err(
"the trait `DispatchFromDyn` may only be implemented \
for structs containing the field being coerced, \
ZST fields, and nothing else"
ZST fields with 1 byte alignment, and nothing else"
).note(
&format!(
"extra field `{}` of type `{}` is not allowed",

9
src/test/ui/invalid_dispatch_from_dyn_impls.rs
View File

@ -39,4 +39,13 @@ where
T: Unsize<U>,
{} //~^^^ ERROR [E0378]
#[repr(align(64))]
struct OverAlignedZst;
struct OverAligned<T: ?Sized>(Box<T>, OverAlignedZst);
impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
where
T: Unsize<U>,
{} //~^^^ ERROR [E0378]
fn main() {}

15
src/test/ui/invalid_dispatch_from_dyn_impls.stderr
View File

@ -1,4 +1,4 @@
error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields, and nothing else
error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment, and nothing else
--> $DIR/invalid_dispatch_from_dyn_impls.rs:10:1
|
LL | / impl<T, U> DispatchFromDyn<WrapperWithExtraField<U>> for WrapperWithExtraField<T>
@ -36,6 +36,17 @@ LL | | T: Unsize<U>,
LL | | {}
| |__^
error: aborting due to 4 previous errors
error[E0378]: the trait `DispatchFromDyn` may only be implemented for structs containing the field being coerced, ZST fields with 1 byte alignment, and nothing else
--> $DIR/invalid_dispatch_from_dyn_impls.rs:46:1
|
LL | / impl<T: ?Sized, U: ?Sized> DispatchFromDyn<OverAligned<U>> for OverAligned<T>
LL | | where
LL | | T: Unsize<U>,
LL | | {}
| |__^
|
= note: extra field `1` of type `OverAlignedZst` is not allowed
error: aborting due to 5 previous errors
For more information about this error, try `rustc --explain E0378`.