mirror of https://github.com/rust-lang/rust
71 lines
2.5 KiB
Rust
71 lines
2.5 KiB
Rust
#![feature(const_mut_refs)]
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#![feature(raw_ref_op)]
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const NULL: *mut i32 = std::ptr::null_mut();
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const A: *const i32 = &4;
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// It could be made sound to allow it to compile,
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// but we do not want to allow this to compile,
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// as that would be an enormous footgun in oli-obk's opinion.
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const B: *mut i32 = &mut 4; //~ ERROR mutable references are not allowed
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// Ok, no actual mutable allocation exists
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const B2: Option<&mut i32> = None;
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// Not ok, can't prove that no mutable allocation ends up in final value
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const B3: Option<&mut i32> = Some(&mut 42); //~ ERROR temporary value dropped while borrowed
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const fn helper(x: &mut i32) -> Option<&mut i32> { Some(x) }
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const B4: Option<&mut i32> = helper(&mut 42); //~ ERROR temporary value dropped while borrowed
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// Ok, because no references to mutable data exist here, since the `{}` moves
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// its value and then takes a reference to that.
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const C: *const i32 = &{
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let mut x = 42;
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x += 3;
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x
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};
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use std::cell::UnsafeCell;
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struct NotAMutex<T>(UnsafeCell<T>);
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unsafe impl<T> Sync for NotAMutex<T> {}
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const FOO: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
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//~^ ERROR temporary value dropped while borrowed
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static FOO2: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
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//~^ ERROR temporary value dropped while borrowed
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static mut FOO3: NotAMutex<&mut i32> = NotAMutex(UnsafeCell::new(&mut 42));
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//~^ ERROR temporary value dropped while borrowed
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// `BAR` works, because `&42` promotes immediately instead of relying on
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// the enclosing scope rule.
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const BAR: NotAMutex<&i32> = NotAMutex(UnsafeCell::new(&42));
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struct SyncPtr<T> { x : *const T }
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unsafe impl<T> Sync for SyncPtr<T> {}
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// These pass the lifetime checks because of the "tail expression" / "outer scope" rule.
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// (This relies on `SyncPtr` being a curly brace struct.)
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// However, we intern the inner memory as read-only, so this must be rejected.
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static RAW_MUT_CAST_S: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
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//~^ ERROR mutable references are not allowed
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static RAW_MUT_COERCE_S: SyncPtr<i32> = SyncPtr { x: &mut 0 };
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//~^ ERROR mutable references are not allowed
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const RAW_MUT_CAST_C: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
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//~^ ERROR mutable references are not allowed
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const RAW_MUT_COERCE_C: SyncPtr<i32> = SyncPtr { x: &mut 0 };
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//~^ ERROR mutable references are not allowed
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fn main() {
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println!("{}", unsafe { *A });
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unsafe { *B = 4 } // Bad news
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unsafe {
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**FOO.0.get() = 99;
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assert_eq!(**FOO.0.get(), 99);
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}
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}
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