150 lines
3.9 KiB
Rust
150 lines
3.9 KiB
Rust
use std::cell::RefCell;
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use std::mem::ManuallyDrop;
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use std::ops::Deref;
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union U1 {
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a: u8,
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}
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union U2 {
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a: ManuallyDrop<String>,
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}
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union U3<T> {
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a: ManuallyDrop<T>,
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}
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union U4<T: Copy> {
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a: T,
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}
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union U5 {
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a: usize,
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}
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union URef {
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p: &'static mut i32,
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}
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union URefCell {
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// field that does not drop but is not `Copy`, either
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a: (ManuallyDrop<RefCell<i32>>, i32),
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}
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fn deref_union_field(mut u: URef) {
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// Not an assignment but an access to the union field!
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*(u.p) = 13; //~ ERROR access to union field is unsafe
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}
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union A {
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a: usize,
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b: &'static &'static B,
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}
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union B {
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c: usize,
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}
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fn raw_deref_union_field(mut u: URef) {
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// This is unsafe because we first dereference u.p (reading uninitialized memory)
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let _p = &raw const *(u.p); //~ ERROR access to union field is unsafe
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}
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fn assign_noncopy_union_field(mut u: URefCell) {
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u.a = (ManuallyDrop::new(RefCell::new(0)), 1); // OK (assignment does not drop)
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u.a.0 = ManuallyDrop::new(RefCell::new(0)); // OK (assignment does not drop)
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u.a.1 = 1; // OK
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}
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fn generic_noncopy<T: Default>() {
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let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
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u3.a = ManuallyDrop::new(T::default()); // OK (assignment does not drop)
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*u3.a = T::default(); //~ ERROR access to union field is unsafe
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}
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fn generic_copy<T: Copy + Default>() {
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let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
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u3.a = ManuallyDrop::new(T::default()); // OK
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*u3.a = T::default(); //~ ERROR access to union field is unsafe
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let mut u4 = U4 { a: T::default() };
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u4.a = T::default(); // OK
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}
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fn main() {
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let mut u1 = U1 { a: 10 }; // OK
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let a = u1.a; //~ ERROR access to union field is unsafe
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u1.a = 11; // OK
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let mut u2 = U1 { a: 10 };
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let a = &raw mut u2.a; // OK
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unsafe { *a = 3 };
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let mut u3 = U1 { a: 10 };
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let a = std::ptr::addr_of_mut!(u3.a); // OK
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unsafe { *a = 14 };
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let u4 = U5 { a: 2 };
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let vec = vec![1, 2, 3];
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// This is unsafe because we read u4.a (potentially uninitialized memory)
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// to use as an array index
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let _a = &raw const vec[u4.a]; //~ ERROR access to union field is unsafe
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let U1 { a } = u1; //~ ERROR access to union field is unsafe
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if let U1 { a: 12 } = u1 {} //~ ERROR access to union field is unsafe
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if let Some(U1 { a: 13 }) = Some(u1) {} //~ ERROR access to union field is unsafe
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// let U1 { .. } = u1; // OK
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let mut u2 = U2 { a: ManuallyDrop::new(String::from("old")) }; // OK
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u2.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
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*u2.a = String::from("new"); //~ ERROR access to union field is unsafe
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let mut u3 = U3 { a: ManuallyDrop::new(0) }; // OK
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u3.a = ManuallyDrop::new(1); // OK
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*u3.a = 1; //~ ERROR access to union field is unsafe
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let mut u3 = U3 { a: ManuallyDrop::new(String::from("old")) }; // OK
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u3.a = ManuallyDrop::new(String::from("new")); // OK (assignment does not drop)
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*u3.a = String::from("new"); //~ ERROR access to union field is unsafe
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let mut unions = [U1 { a: 1 }, U1 { a: 2 }];
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// Array indexing + union field raw borrow - should be OK
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let ptr = &raw mut unions[0].a; // OK
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let ptr2 = &raw const unions[1].a; // OK
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let a = A { a: 0 };
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let _p = &raw const (**a.b).c; //~ ERROR access to union field is unsafe
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arbitrary_deref();
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}
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// regression test for https://github.com/rust-lang/rust/pull/141469#discussion_r2312546218
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fn arbitrary_deref() {
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use std::ops::Deref;
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union A {
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a: usize,
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b: B,
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}
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#[derive(Copy, Clone)]
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struct B(&'static str);
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impl Deref for B {
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type Target = C;
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fn deref(&self) -> &C {
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println!("{:?}", self.0);
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&C { c: 0 }
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}
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}
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union C {
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c: usize,
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}
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let a = A { a: 0 };
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let _p = &raw const (*a.b).c; //~ ERROR access to union field is unsafe
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}
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