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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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6
compiler/rustc_middle/src/mir/query.rs
View File

@ -35,7 +35,6 @@ pub enum UnsafetyViolationDetails {
UseOfMutableStatic,
UseOfExternStatic,
DerefOfRawPointer,
AssignToDroppingUnionField,
AccessToUnionField,
MutationOfLayoutConstrainedField,
BorrowOfLayoutConstrainedField,
@ -78,11 +77,6 @@ impl UnsafetyViolationDetails {
"raw pointers may be null, dangling or unaligned; they can violate aliasing rules \
and cause data races: all of these are undefined behavior",
),
AssignToDroppingUnionField => (
"assignment to union field that might need dropping",
"the previous content of the field will be dropped, which causes undefined \
behavior if the field was not properly initialized",
),
AccessToUnionField => (
"access to union field",
"the field may not be properly initialized: using uninitialized data will cause \

20
compiler/rustc_mir_build/src/check_unsafety.rs
View File

@ -431,16 +431,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
let lhs = &self.thir[lhs];
if let ty::Adt(adt_def, _) = lhs.ty.kind() && adt_def.is_union() {
if let Some((assigned_ty, assignment_span)) = self.assignment_info {
// To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
if !(assigned_ty
.ty_adt_def()
.map_or(false, |adt| adt.is_manually_drop())
|| assigned_ty
.is_copy_modulo_regions(self.tcx.at(expr.span), self.param_env))
{
self.requires_unsafe(assignment_span, AssignToDroppingUnionField);
} else {
// write to non-drop union field, safe
if assigned_ty.needs_drop(self.tcx, self.tcx.param_env(adt_def.did())) {
// This would be unsafe, but should be outright impossible since we reject such unions.
self.tcx.sess.delay_span_bug(assignment_span, "union fields that need dropping should be impossible");
}
} else {
self.requires_unsafe(expr.span, AccessToUnionField);
@ -537,7 +530,6 @@ enum UnsafeOpKind {
UseOfMutableStatic,
UseOfExternStatic,
DerefOfRawPointer,
AssignToDroppingUnionField,
AccessToUnionField,
MutationOfLayoutConstrainedField,
BorrowOfLayoutConstrainedField,
@ -555,7 +547,6 @@ impl UnsafeOpKind {
UseOfMutableStatic => "use of mutable static",
UseOfExternStatic => "use of extern static",
DerefOfRawPointer => "dereference of raw pointer",
AssignToDroppingUnionField => "assignment to union field that might need dropping",
AccessToUnionField => "access to union field",
MutationOfLayoutConstrainedField => "mutation of layout constrained field",
BorrowOfLayoutConstrainedField => {
@ -600,11 +591,6 @@ impl UnsafeOpKind {
"raw pointers may be null, dangling or unaligned; they can violate aliasing rules \
and cause data races: all of these are undefined behavior",
),
AssignToDroppingUnionField => (
Cow::Borrowed(self.simple_description()),
"the previous content of the field will be dropped, which causes undefined \
behavior if the field was not properly initialized",
),
AccessToUnionField => (
Cow::Borrowed(self.simple_description()),
"the field may not be properly initialized: using uninitialized data will cause \

23
compiler/rustc_mir_transform/src/check_unsafety.rs
View File

@ -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(

10
src/test/ui/union/union-unsafe.mir.stderr
View File

@ -6,14 +6,6 @@ LL | *(u.p) = 13;
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: assignment to union field that might need dropping is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:38:5
|
LL | u.a = (ManuallyDrop::new(RefCell::new(0)), 1);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to union field that might need dropping
|
= note: the previous content of the field will be dropped, which causes undefined behavior if the field was not properly initialized
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:46:6
|
@ -78,6 +70,6 @@ LL | *u3.a = String::from("new");
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error: aborting due to 10 previous errors
error: aborting due to 9 previous errors
For more information about this error, try `rustc --explain E0133`.

2
src/test/ui/union/union-unsafe.rs
View File

@ -35,7 +35,7 @@ fn deref_union_field(mut u: URef) {
fn assign_noncopy_union_field(mut u: URefCell) {
// FIXME(thir-unsafeck)
u.a = (ManuallyDrop::new(RefCell::new(0)), 1); //~ ERROR assignment to union field
u.a = (ManuallyDrop::new(RefCell::new(0)), 1); // OK (assignment does not drop)
u.a.0 = ManuallyDrop::new(RefCell::new(0)); // OK (assignment does not drop)
u.a.1 = 1; // OK
}

10
src/test/ui/union/union-unsafe.thir.stderr
View File

@ -6,14 +6,6 @@ LL | *(u.p) = 13;
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: assignment to union field that might need dropping is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:38:5
|
LL | u.a = (ManuallyDrop::new(RefCell::new(0)), 1);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to union field that might need dropping
|
= note: the previous content of the field will be dropped, which causes undefined behavior if the field was not properly initialized
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:46:6
|
@ -78,6 +70,6 @@ LL | *u3.a = String::from("new");
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error: aborting due to 10 previous errors
error: aborting due to 9 previous errors
For more information about this error, try `rustc --explain E0133`.