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rust-bors merged 1 commit into from
Aug 15, 2026
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tests/ui/union: add annotations for reference rules #152826

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2 changes: 2 additions & 0 deletions tests/ui/union/access_union_field.rs
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//@ reference: items.union.fields.read-safety
//@ reference: type.union.safety
#![allow(unused_variables)]

union Foo {
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4 changes: 2 additions & 2 deletions tests/ui/union/access_union_field.stderr
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error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/access_union_field.rs:10:13
--> $DIR/access_union_field.rs:12:13
|
LL | let a = foo.bar;
| ^^^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/access_union_field.rs:11:13
--> $DIR/access_union_field.rs:13:13
|
LL | let b = foo.baz;
| ^^^^^^^ access to union field
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7 changes: 7 additions & 0 deletions tests/ui/union/field_checks.rs
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@@ -1,3 +1,10 @@
//@ reference: items.union.drop
//@ reference: items.union.field-restrictions
//@ reference: items.union.field-copy
//@ reference: items.union.field-references
//@ reference: items.union.field-manually-drop
//@ reference: items.union.field-tuple
//@ reference: type.union.constraint
Comment thread
DanielEScherzer marked this conversation as resolved.
use std::mem::ManuallyDrop;

union U1 { // OK
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10 changes: 5 additions & 5 deletions tests/ui/union/field_checks.stderr
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error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/field_checks.rs:24:5
--> $DIR/field_checks.rs:31:5
|
LL | a: String,
| ^^^^^^^^^
Expand All @@ -11,7 +11,7 @@ LL | a: std::mem::ManuallyDrop<String>,
| +++++++++++++++++++++++ +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/field_checks.rs:28:5
--> $DIR/field_checks.rs:35:5
|
LL | a: std::cell::RefCell<i32>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -23,7 +23,7 @@ LL | a: std::mem::ManuallyDrop<std::cell::RefCell<i32>>,
| +++++++++++++++++++++++ +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/field_checks.rs:32:5
--> $DIR/field_checks.rs:39:5
|
LL | a: T,
| ^^^^
Expand All @@ -35,7 +35,7 @@ LL | a: std::mem::ManuallyDrop<T>,
| +++++++++++++++++++++++ +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/field_checks.rs:44:5
--> $DIR/field_checks.rs:51:5
|
LL | nest: U5,
| ^^^^^^^^
Expand All @@ -47,7 +47,7 @@ LL | nest: std::mem::ManuallyDrop<U5>,
| +++++++++++++++++++++++ +

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/field_checks.rs:48:5
--> $DIR/field_checks.rs:55:5
|
LL | nest: [U5; 0],
| ^^^^^^^^^^^^^
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2 changes: 2 additions & 0 deletions tests/ui/union/issue-41073.rs
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//@ reference: items.union.field-restrictions
//@ reference: type.union.constraint
union Test {
a: A, //~ ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
b: B
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2 changes: 1 addition & 1 deletion tests/ui/union/issue-41073.stderr
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error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/issue-41073.rs:2:5
--> $DIR/issue-41073.rs:4:5
|
LL | a: A,
| ^^^^
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2 changes: 2 additions & 0 deletions tests/ui/union/issue-81199.rs
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//@ reference: items.union.field-restrictions
//@ reference: type.union.constraint
#[repr(C)]
union PtrRepr<T: ?Sized> {
const_ptr: *const T,
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6 changes: 3 additions & 3 deletions tests/ui/union/issue-81199.stderr
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error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
--> $DIR/issue-81199.rs:5:5
--> $DIR/issue-81199.rs:7:5
|
LL | components: PtrComponents<T>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -11,14 +11,14 @@ LL | components: std::mem::ManuallyDrop<PtrComponents<T>>,
| +++++++++++++++++++++++ +

error[E0277]: the trait bound `T: Pointee` is not satisfied
--> $DIR/issue-81199.rs:5:17
--> $DIR/issue-81199.rs:7:17
|
LL | components: PtrComponents<T>,
| ^^^^^^^^^^^^^^^^ the trait `Pointee` is not implemented for `T`
|
= note: `T` implements similarly named trait `std::ptr::Pointee`, but not `Pointee`
note: required by a bound in `PtrComponents`
--> $DIR/issue-81199.rs:11:25
--> $DIR/issue-81199.rs:13:25
|
LL | struct PtrComponents<T: Pointee + ?Sized> {
| ^^^^^^^ required by this bound in `PtrComponents`
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2 changes: 2 additions & 0 deletions tests/ui/union/issue-99375.rs
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//@ check-pass
//@ reference: items.union.field-copy
//@ reference: items.union.field-tuple

union URes<R: Copy> {
uninit: (),
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2 changes: 2 additions & 0 deletions tests/ui/union/union-assignop.rs
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//@ reference: items.union.fields.read-safety
//@ reference: items.union.fields.write-safety
use std::ops::AddAssign;
use std::mem::ManuallyDrop;

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12 changes: 6 additions & 6 deletions tests/ui/union/union-assignop.stderr
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error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:16:5
--> $DIR/union-assignop.rs:18:5
|
LL | foo.a += 5;
| ^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:17:6
--> $DIR/union-assignop.rs:19:6
|
LL | *foo.b += NonCopy;
| ^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:18:6
--> $DIR/union-assignop.rs:20:6
|
LL | *foo.b = NonCopy;
| ^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:20:5
--> $DIR/union-assignop.rs:22:5
|
LL | foo.a;
| ^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:22:5
--> $DIR/union-assignop.rs:24:5
|
LL | foo.b;
| ^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior

error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-assignop.rs:24:13
--> $DIR/union-assignop.rs:26:13
|
LL | foo.b = foo.b;
| ^^^^^ access to union field
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1 change: 1 addition & 0 deletions tests/ui/union/union-backcomp.rs
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//@ run-pass
//@ reference: lex.keywords.weak.union

#![allow(path_statements)]
#![allow(dead_code)]
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1 change: 1 addition & 0 deletions tests/ui/union/union-borrow-move-parent-sibling.rs
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//@ reference: items.union.ref.borrow
#![allow(unused)]

use std::ops::{Deref, DerefMut};
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20 changes: 10 additions & 10 deletions tests/ui/union/union-borrow-move-parent-sibling.stderr
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error[E0502]: cannot borrow `u` (via `u.y`) as immutable because it is also borrowed as mutable (via `u.x`)
--> $DIR/union-borrow-move-parent-sibling.rs:53:13
--> $DIR/union-borrow-move-parent-sibling.rs:54:13
|
LL | let a = &mut (*u.x).0;
| --- mutable borrow occurs here (via `u.x`)
Expand All @@ -11,7 +11,7 @@ LL | use_borrow(a);
= note: `u.y` is a field of the union `U`, so it overlaps the field `u.x`

error[E0507]: cannot move out of dereference of `ManuallyDrop<((MockVec<u8>, MockVec<u8>), MockVec<u8>)>`
--> $DIR/union-borrow-move-parent-sibling.rs:59:13
--> $DIR/union-borrow-move-parent-sibling.rs:60:13
|
LL | let a = u.x.0;
| ^^^^^ move occurs because value has type `(MockVec<u8>, MockVec<u8>)`, which does not implement the `Copy` trait
Expand All @@ -22,7 +22,7 @@ LL | let a = &u.x.0;
| +

error[E0382]: use of moved value: `u`
--> $DIR/union-borrow-move-parent-sibling.rs:61:13
--> $DIR/union-borrow-move-parent-sibling.rs:62:13
|
LL | let u = U { x: ManuallyDrop::new(((MockVec::new(), MockVec::new()), MockVec::new())) };
| - move occurs because `u` has type `U`, which does not implement the `Copy` trait
Expand All @@ -33,7 +33,7 @@ LL | let b = u.y;
| ^^^ value used here after move
|
note: if `U` implemented `Clone`, you could clone the value
--> $DIR/union-borrow-move-parent-sibling.rs:43:1
--> $DIR/union-borrow-move-parent-sibling.rs:44:1
|
LL | union U {
| ^^^^^^^ consider implementing `Clone` for this type
Expand All @@ -42,7 +42,7 @@ LL | let a = u.x;
| --- you could clone this value

error[E0502]: cannot borrow `u` (via `u.y`) as immutable because it is also borrowed as mutable (via `u.x`)
--> $DIR/union-borrow-move-parent-sibling.rs:67:13
--> $DIR/union-borrow-move-parent-sibling.rs:68:13
|
LL | let a = &mut ((*u.x).0).0;
| --- mutable borrow occurs here (via `u.x`)
Expand All @@ -54,13 +54,13 @@ LL | use_borrow(a);
= note: `u.y` is a field of the union `U`, so it overlaps the field `u.x`

error[E0507]: cannot move out of dereference of `ManuallyDrop<((MockVec<u8>, MockVec<u8>), MockVec<u8>)>`
--> $DIR/union-borrow-move-parent-sibling.rs:73:13
--> $DIR/union-borrow-move-parent-sibling.rs:74:13
|
LL | let a = (u.x.0).0;
| ^^^^^^^^^ move occurs because value has type `MockVec<u8>`, which does not implement the `Copy` trait
|
note: if `MockVec<u8>` implemented `Clone`, you could clone the value
--> $DIR/union-borrow-move-parent-sibling.rs:25:1
--> $DIR/union-borrow-move-parent-sibling.rs:26:1
|
LL | struct MockVec<T> {
| ^^^^^^^^^^^^^^^^^ consider implementing `Clone` for this type
Expand All @@ -73,7 +73,7 @@ LL | let a = &(u.x.0).0;
| +

error[E0382]: use of moved value: `u`
--> $DIR/union-borrow-move-parent-sibling.rs:75:13
--> $DIR/union-borrow-move-parent-sibling.rs:76:13
|
LL | let u = U { x: ManuallyDrop::new(((MockVec::new(), MockVec::new()), MockVec::new())) };
| - move occurs because `u` has type `U`, which does not implement the `Copy` trait
Expand All @@ -84,7 +84,7 @@ LL | let b = u.y;
| ^^^ value used here after move
|
note: if `U` implemented `Clone`, you could clone the value
--> $DIR/union-borrow-move-parent-sibling.rs:43:1
--> $DIR/union-borrow-move-parent-sibling.rs:44:1
|
LL | union U {
| ^^^^^^^ consider implementing `Clone` for this type
Expand All @@ -93,7 +93,7 @@ LL | let a = u.x;
| --- you could clone this value

error[E0502]: cannot borrow `u` (via `u.x`) as immutable because it is also borrowed as mutable (via `u.y`)
--> $DIR/union-borrow-move-parent-sibling.rs:81:13
--> $DIR/union-borrow-move-parent-sibling.rs:82:13
|
LL | let a = &mut *u.y;
| --- mutable borrow occurs here (via `u.y`)
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1 change: 1 addition & 0 deletions tests/ui/union/union-copy.rs
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//@ reference: lang-types.copy.constraint
#[derive(Clone)]
union U {
a: u8
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4 changes: 2 additions & 2 deletions tests/ui/union/union-copy.stderr
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error[E0204]: the trait `Copy` cannot be implemented for this type
--> $DIR/union-copy.rs:12:15
--> $DIR/union-copy.rs:13:15
|
LL | a: std::mem::ManuallyDrop<String>
| --------------------------------- this field does not implement `Copy`
Expand All @@ -8,7 +8,7 @@ LL | impl Copy for W {}
| ^
|
note: the `Copy` impl for `ManuallyDrop<String>` requires that `String: Copy`
--> $DIR/union-copy.rs:8:8
--> $DIR/union-copy.rs:9:8
|
LL | a: std::mem::ManuallyDrop<String>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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1 change: 1 addition & 0 deletions tests/ui/union/union-drop-assign.rs
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//@ run-pass
//@ reference: items.union.drop
#![allow(unused_assignments)]

// Drop works for union itself.
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2 changes: 2 additions & 0 deletions tests/ui/union/union-drop.rs
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//@ run-pass
//@ reference: destructors.manually-suppressing
//@ reference: items.union.drop
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DanielEScherzer marked this conversation as resolved.

#![allow(dead_code)]
#![allow(unused_variables)]
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1 change: 1 addition & 0 deletions tests/ui/union/union-empty.rs
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//@ reference: items.union.fieldless
union U {} //~ ERROR unions cannot have zero fields

fn main() {}
2 changes: 1 addition & 1 deletion tests/ui/union/union-empty.stderr
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error: unions cannot have zero fields
--> $DIR/union-empty.rs:1:1
--> $DIR/union-empty.rs:2:1
|
LL | union U {}
| ^^^^^^^^^^
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4 changes: 4 additions & 0 deletions tests/ui/union/union-fields-2.rs
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//@ reference: expr.struct.field.union-constraint
//@ reference: items.union.init.intro
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//@ reference: items.union.pattern.one-field
//@ reference: patterns.struct.constraint-union
union U {
a: u8,
b: u16,
Expand Down
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