bjoernager/rust
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only emit error for ManuallyDrop derefs

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This commit is contained in:
Ralf Jung 2020-08-16 10:32:37 +02:00
parent 44defaea3a
commit 97974e3cab
3 changed files with 18 additions and 13 deletions
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14
compiler/rustc_typeck/src/check/place_op.rs
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@ -244,14 +244,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
if let ty::Ref(region, _, mutbl) = method.sig.output().kind {
*deref = OverloadedDeref { region, mutbl };
}
// If this is a union field, also throw an error.
// Union fields should not get mutable auto-deref'd (see RFC 2514).
if inside_union {
// If this is a union field, also throw an error for `DerefMut` of `ManuallyDrop` (see RFC 2514).
// This helps avoid accidental drops.
if inside_union
&& source.ty_adt_def().map_or(false, |adt| adt.is_manually_drop())
{
let mut err = self.tcx.sess.struct_span_err(
expr.span,
"not automatically applying `DerefMut` on union field",
"not automatically applying `DerefMut` on `ManuallyDrop` union field",
);
err.help(
"writing to this reference calls the destructor for the old value",
);
err.help("writing to this field calls the destructor for the old value");
err.help("add an explicit `*` if that is desired, or call `ptr::write` to not run the destructor");
err.emit();
}