Commits on Nov 29, 2025

1. Unrolled build for#148746 …

   Rollup merge of#148746 - RalfJung:mutable-ref-in-const, r=davidtwcoconst validation: remove check for mutable refs in final value of constThis check rejects code that is not necessarily UB, e.g. a mutable ref to a `static mut` that is very carefully used correctly. That led to us having to describe it in the Reference, which uncovered just how ad-hoc this check is (rust-lang/reference#2074).Even without this check, we still reject things like```rustconst C: &mut i32 = &mut 0;```This is rejected by const checking -- the part of the frontend that looks at the source code and says whether it is allowed in const context. In the Reference, this restriction is explained [here](https://doc.rust-lang.org/nightly/reference/const_eval.html#r-const-eval.const-expr.borrows).So, the check during validation is just a safety net. And it is already a safety net with gaping holes since we only check `&mut T`, not `&UnsafeCell<T>`, due to the fact that we promote some immutable values that have `!Freeze` type so `&!Freeze` actually can occur in the final value of a const.So... it may be time for me to acknowledge that the "mutable ref in final value of const" check is a cure that's worth than the disease. Nobody asked for that check, I just added it because I was worried about soundness issues when we allow mutable references in constants. Originally it was much stricter, but I had to slowly relax it to its current form to prevent t from firing on code we intend to allow. In the end there are only 3 tests left that trigger this error, and they are all just constants containing references to mutable statics -- not the safest code in the world, but also not so bad that we have to spend a lot of time devising a core language limitation and associated Reference wording to prevent it from ever happening.So... `@rust-lang/wg-const-eval` `@rust-lang/lang`  I propose that we allow code like this```ruststatic mut S: i32 = 3;const C2: &'static mut i32 = unsafe { &mut * &raw mut S };````@theemathas` would be great if you could try to poke a hole into this. ;)

   

   rust-timer authoredNov 29, 2025
   Configuration menu

   • View commit details
   • Copy full SHA for fa3c1be
   • Browse repository at this point

   Copy the full SHA

   fa3c1beView commit details

   Browse the repository at this point in the history