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consider assignments of union field of ManuallyDrop type safe

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This commit is contained in:
Ralf Jung 2020-10-18 13:53:54 +02:00
parent 3d3c8c5e0d
commit 3ac1df8b99
4 changed files with 35 additions and 56 deletions
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6
compiler/rustc_middle/src/mir/query.rs
View File

@ -46,7 +46,7 @@ pub enum UnsafetyViolationDetails {
UseOfMutableStatic,
UseOfExternStatic,
DerefOfRawPointer,
AssignToNonCopyUnionField,
AssignToDroppingUnionField,
AccessToUnionField,
MutationOfLayoutConstrainedField,
BorrowOfLayoutConstrainedField,
@ -94,8 +94,8 @@ 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",
),
AssignToNonCopyUnionField => (
"assignment to non-`Copy` union field",
AssignToDroppingUnionField => (
"assignment to union field that needs dropping",
"the previous content of the field will be dropped, which causes undefined \
behavior if the field was not properly initialized",
),

53
compiler/rustc_mir/src/transform/check_unsafety.rs
View File

@ -235,37 +235,40 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationDetails::DerefOfRawPointer,
),
ty::Adt(adt, _) => {
if adt.is_union() {
if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
|| context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
|| context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
{
let elem_ty = match elem {
ProjectionElem::Field(_, ty) => ty,
_ => span_bug!(
self.source_info.span,
"non-field projection {:?} from union?",
place
),
};
if !elem_ty.is_copy_modulo_regions(
ty::Adt(adt, _) if adt.is_union() => {
if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
|| context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
|| context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
{
let elem_ty = match elem {
ProjectionElem::Field(_, ty) => ty,
_ => span_bug!(
self.source_info.span,
"non-field projection {:?} from union?",
place
),
};
let manually_drop = elem_ty
.ty_adt_def()
.map_or(false, |adt_def| adt_def.is_manually_drop());
let nodrop = manually_drop
|| elem_ty.is_copy_modulo_regions(
self.tcx.at(self.source_info.span),
self.param_env,
) {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationDetails::AssignToNonCopyUnionField,
)
} else {
// write to non-move union, safe
}
} else {
);
if !nodrop {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationDetails::AccessToUnionField,
UnsafetyViolationDetails::AssignToDroppingUnionField,
)
} else {
// write to non-drop union field, safe
}
} else {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationDetails::AccessToUnionField,
)
}
}
_ => {}

6
src/test/ui/union/union-unsafe.rs
View File

@ -18,7 +18,7 @@ union U4<T: Copy> {
fn generic_noncopy<T: Default>() {
let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
u3.a = ManuallyDrop::new(T::default()); //~ ERROR assignment to non-`Copy` union field is unsafe
u3.a = ManuallyDrop::new(T::default()); // OK (assignment does not drop)
*u3.a = T::default(); //~ ERROR access to union field is unsafe
}
@ -41,7 +41,7 @@ fn main() {
// let U1 { .. } = u1; // OK
let mut u2 = U2 { a: ManuallyDrop::new(String::from("old")) }; // OK
u2.a = ManuallyDrop::new(String::from("new")); //~ ERROR assignment to non-`Copy` union
u2.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
*u2.a = String::from("new"); //~ ERROR access to union field is unsafe
let mut u3 = U3 { a: ManuallyDrop::new(0) }; // OK
@ -49,6 +49,6 @@ fn main() {
*u3.a = 1; //~ ERROR access to union field is unsafe
let mut u3 = U3 { a: ManuallyDrop::new(String::from("old")) }; // OK
u3.a = ManuallyDrop::new(String::from("new")); //~ ERROR assignment to non-`Copy` union
u3.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
*u3.a = String::from("new"); //~ ERROR access to union field is unsafe
}

26
src/test/ui/union/union-unsafe.stderr
View File

@ -1,11 +1,3 @@
error[E0133]: assignment to non-`Copy` union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:21:5
|
LL | u3.a = ManuallyDrop::new(T::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to non-`Copy` union field
|
= 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:22:6
|
@ -46,14 +38,6 @@ LL | if let U1 { a: 12 } = u1 {}
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: assignment to non-`Copy` union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:44:5
|
LL | u2.a = ManuallyDrop::new(String::from("new"));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to non-`Copy` union field
|
= 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:45:6
|
@ -70,14 +54,6 @@ LL | *u3.a = 1;
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: assignment to non-`Copy` union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:52:5
|
LL | u3.a = ManuallyDrop::new(String::from("new"));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to non-`Copy` union field
|
= 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:53:6
|
@ -86,6 +62,6 @@ 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 11 previous errors
error: aborting due to 8 previous errors
For more information about this error, try `rustc --explain E0133`.