assigning to a union field can never drop now
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6 changed files with 14 additions and 57 deletions
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@ -431,16 +431,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
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let lhs = &self.thir[lhs];
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if let ty::Adt(adt_def, _) = lhs.ty.kind() && adt_def.is_union() {
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if let Some((assigned_ty, assignment_span)) = self.assignment_info {
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// To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
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if !(assigned_ty
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.ty_adt_def()
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.map_or(false, |adt| adt.is_manually_drop())
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|| assigned_ty
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.is_copy_modulo_regions(self.tcx.at(expr.span), self.param_env))
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{
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self.requires_unsafe(assignment_span, AssignToDroppingUnionField);
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} else {
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// write to non-drop union field, safe
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if assigned_ty.needs_drop(self.tcx, self.tcx.param_env(adt_def.did())) {
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// This would be unsafe, but should be outright impossible since we reject such unions.
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self.tcx.sess.delay_span_bug(assignment_span, "union fields that need dropping should be impossible");
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}
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} else {
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self.requires_unsafe(expr.span, AccessToUnionField);
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@ -537,7 +530,6 @@ enum UnsafeOpKind {
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UseOfMutableStatic,
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UseOfExternStatic,
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DerefOfRawPointer,
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AssignToDroppingUnionField,
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AccessToUnionField,
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MutationOfLayoutConstrainedField,
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BorrowOfLayoutConstrainedField,
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@ -555,7 +547,6 @@ impl UnsafeOpKind {
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UseOfMutableStatic => "use of mutable static",
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UseOfExternStatic => "use of extern static",
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DerefOfRawPointer => "dereference of raw pointer",
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AssignToDroppingUnionField => "assignment to union field that might need dropping",
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AccessToUnionField => "access to union field",
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MutationOfLayoutConstrainedField => "mutation of layout constrained field",
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BorrowOfLayoutConstrainedField => {
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@ -600,11 +591,6 @@ impl UnsafeOpKind {
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"raw pointers may be null, dangling or unaligned; they can violate aliasing rules \
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and cause data races: all of these are undefined behavior",
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),
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AssignToDroppingUnionField => (
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Cow::Borrowed(self.simple_description()),
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"the previous content of the field will be dropped, which causes undefined \
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behavior if the field was not properly initialized",
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),
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AccessToUnionField => (
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Cow::Borrowed(self.simple_description()),
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"the field may not be properly initialized: using uninitialized data will cause \
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