Using &raw const instead of &raw mut does not offer a suggestion fix

Code

fn main() {
    let val = 2;
    let ptr = &raw const val;
    unsafe { *ptr = 3; }
}

Current output

error[E0594]: cannot assign to `*ptr`, which is behind a `*const` pointer
 --> src/main.rs:4:14
  |
4 |     unsafe { *ptr = 3; }
  |              ^^^^^^^^ `ptr` is a `*const` pointer, so the data it refers to cannot be written

For more information about this error, try `rustc --explain E0594`.

Desired output

error[E0594]: cannot assign to `*ptr`, which is behind a `*const` pointer
 --> src/main.rs:4:14
  |
4 |     unsafe { *ptr = 3; }
  |              ^^^^^^^^ `ptr` is a `*const` pointer, so the data it refers to cannot be written
  |
help: consider changing this to be a mutable pointer
  |
3 |     let ptr = &raw mut val;
  |                    ~~~

For more information about this error, try `rustc --explain E0594`.

Rationale and extra context

The current error message does not include a suggestion for how to fix it.

Other cases

No response

Rust Version

1.85.0-nightly (2024-12-14 0aeaa5eb22180fdf12a8)

Anything else?

EDIT 1: updated since addr_of! and addr_of_mut! diagnostics are not incorrect anymore due to #127675
EDIT 2: updated as #134224 removed the invalid suggestion

I think the current suggestion is suggesting the code like this:

    let ptr = &mut val;

oh, the suggestion's code comes from here:

https://github.com/chenyukang/rust/blob/c8ed5c50edfd1b721c0541fa614864179251aaac/library/core/src/ptr/mod.rs#L2208

I think we should not suggest to change the library code here.

I have playground link that represents the problem above: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=fee632ddd4f51a0390ac6918ef4eff96

However, when I add that code as a regression tests in tests/ui directory, the diagnostic suddenly changed to

error[E0594]: cannot assign to `*ptr`, which is behind a `*const` pointer
  --> $DIR/dont_suggest_raw_pointer_syntax-issue-127562.rs:9:9
   |
LL |         *ptr = 3;
   |         ^^^^^^^^ `ptr` is a `*const` pointer, so the data it refers to cannot be written
   |
help: consider specifying this binding's type
   |
LL |     let ptr: *mut i32 = std::ptr::addr_of!(val);
   |            ++++++++++

I don't have any ideas about this differences.

binding's type

This is because when run the test UI, the span here is remaped $SRC_DIR/core/src/ptr/mod.rs:LL:COL (#4):
https://github.com/chenyukang/rust/blob/b44a48416d06524da2ea247f1d1973d85ef514f8/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs#L1452

so the here we get an error and didn't continue the code branch:
https://github.com/chenyukang/rust/blob/b44a48416d06524da2ea247f1d1973d85ef514f8/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs#L1453

it's weird, maybe another issue need to be fixed.

Given that &raw syntax might get stabilized soon by #127679, suggesting the correct &raw mut syntax would become a more feasible option.

&mut raw const $place

This is completely invalid syntax so just suggesting nothing instead as a first step would already be a good idea.

Suggesting anything that involves references is a really bad idea -- code that uses raw pointers should keep using raw pointers throughout with no intermediate references.

Rollup merge of rust-lang#127675 - chenyukang:yukang-fix-127562-addr,…

Unrolled build for rust-lang#127675

Rollup merge of rust-lang#134244 - Enselic:no-mut-hint-for-raw-ref, r…

Unrolled build for rust-lang#134244

With #134244 we now at least don't suggest invalid syntax.

But it would be even nicer to suggest changing &raw const val to &raw mut val (which when applied will then suggest changing to let mut val).

@rustbot

@rustbot label: -D-invalid-suggestion

Rollup merge of rust-lang#134397 - Enselic:raw-mut, r=compiler-errors

Unrolled build for rust-lang#134397

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Using `&raw const` instead of `&raw mut` does not offer a suggestion fix #127562

Code

Current output

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Rationale and extra context

Other cases

Rust Version

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Using &raw const instead of &raw mut does not offer a suggestion fix #127562

Description

Code

Current output

Desired output

Rationale and extra context

Other cases

Rust Version

Anything else?

Activity

chenyukang commented on Jul 13, 2024

chenyukang commented on Jul 13, 2024

tesuji commented on Jul 13, 2024

chenyukang commented on Jul 13, 2024

cyrgani commented on Jul 14, 2024

RalfJung commented on Jul 14, 2024

Enselic commented on Dec 14, 2024

cyrgani commented on Dec 15, 2024

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Using `&raw const` instead of `&raw mut` does not offer a suggestion fix #127562