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assigning to a union field can never drop now

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This commit is contained in:
Ralf Jung 2022-06-30 08:40:06 -04:00
parent 5bf6017b87
commit e4593ef0f2
6 changed files with 14 additions and 57 deletions
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23
compiler/rustc_mir_transform/src/check_unsafety.rs
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@ -219,22 +219,15 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
// We have to check the actual type of the assignment, as that determines if the
// old value is being dropped.
let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
// To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
let manually_drop = assigned_ty
.ty_adt_def()
.map_or(false, |adt_def| adt_def.is_manually_drop());
let nodrop = manually_drop
|| assigned_ty.is_copy_modulo_regions(
self.tcx.at(self.source_info.span),
self.param_env,
if assigned_ty.needs_drop(
self.tcx,
self.tcx.param_env(base_ty.ty_adt_def().unwrap().did()),
) {
// This would be unsafe, but should be outright impossible since we reject such unions.
self.tcx.sess.delay_span_bug(
self.source_info.span,
"union fields that need dropping should be impossible",
);
if !nodrop {
self.require_unsafe(
UnsafetyViolationKind::General,
UnsafetyViolationDetails::AssignToDroppingUnionField,
);
} else {
// write to non-drop union field, safe
}
} else {
self.require_unsafe(