diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs index db0056e482b..03faef4d9fa 100644 --- a/compiler/rustc_middle/src/mir/query.rs +++ b/compiler/rustc_middle/src/mir/query.rs @@ -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", ), diff --git a/compiler/rustc_mir/src/transform/check_unsafety.rs b/compiler/rustc_mir/src/transform/check_unsafety.rs index acec3e8f82f..fdc033f9eb3 100644 --- a/compiler/rustc_mir/src/transform/check_unsafety.rs +++ b/compiler/rustc_mir/src/transform/check_unsafety.rs @@ -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, + ) } } _ => {} diff --git a/src/test/ui/union/union-unsafe.rs b/src/test/ui/union/union-unsafe.rs index 10f0c467560..9810ed75d59 100644 --- a/src/test/ui/union/union-unsafe.rs +++ b/src/test/ui/union/union-unsafe.rs @@ -18,7 +18,7 @@ union U4 { fn generic_noncopy() { 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 } diff --git a/src/test/ui/union/union-unsafe.stderr b/src/test/ui/union/union-unsafe.stderr index b50d9e17506..5b3a58814a9 100644 --- a/src/test/ui/union/union-unsafe.stderr +++ b/src/test/ui/union/union-unsafe.stderr @@ -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`.