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Rollup merge of #130107 - RalfJung:const-ptr-is-null, r=oli-obk
const: make ptr.is_null() stop execution on ambiguity This seems better than saying `false` -- saying `false` is in fact actively unsound if `NonNull` then uses this to permit putting this pointer inside of it, but at runtime it turns out to be null. Part of #74939 Cc ``@rust-lang/wg-const-eval``
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,20 @@ | ||
#![feature(const_ptr_is_null)] | ||
use std::ptr; | ||
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const IS_NULL: () = { | ||
assert!(ptr::null::<u8>().is_null()); | ||
}; | ||
const IS_NOT_NULL: () = { | ||
assert!(!ptr::null::<u8>().wrapping_add(1).is_null()); | ||
}; | ||
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const MAYBE_NULL: () = { | ||
let x = 15; | ||
let ptr = &x as *const i32; | ||
// This one is still unambiguous... | ||
assert!(!ptr.is_null()); | ||
// but once we shift outside the allocation, we might become null. | ||
assert!(!ptr.wrapping_sub(512).is_null()); //~inside `MAYBE_NULL` | ||
}; | ||
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fn main() {} |
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Original file line number | Diff line number | Diff line change |
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error[E0080]: evaluation of constant value failed | ||
--> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
| | ||
= note: the evaluated program panicked at 'null-ness of this pointer cannot be determined in const context', $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
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note: inside `std::ptr::const_ptr::<impl *const T>::is_null::const_impl` | ||
--> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
note: inside `std::ptr::const_ptr::<impl *const i32>::is_null` | ||
--> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL | ||
note: inside `MAYBE_NULL` | ||
--> $DIR/const-ptr-is-null.rs:17:14 | ||
| | ||
LL | assert!(!ptr.wrapping_sub(512).is_null()); | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
= note: this error originates in the macro `$crate::panic::panic_2021` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info) | ||
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error: aborting due to 1 previous error | ||
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For more information about this error, try `rustc --explain E0080`. |