Can't call `unreachable!()` in const functions

I tried this code:

const fn foo() {
    unreachable!("Hello");
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=921692a8d3cfdee072d1719552003961

I expected to see this happen:
Code compiles

Instead, this happened:

error[E0015]: cannot call non-const formatting macro in constant functions
 --> src/lib.rs:2:5
  |
2 |     unreachable!("Hello");
  |     ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants

This happens on both stable and nightly. Almost identical panic!() macro works fine, so I expect unreachable!() and todo!() to work as well, as long as no formatting is applied to the provided string.

Meta

rustc --version --verbose:

rustc 1.99.0-nightly (d0babd8b6 2026-07-15)
binary: rustc
commit-hash: d0babd8b6b05ef9bb65d42f928cef4129d64cf65
commit-date: 2026-07-15
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8

Reproduce the reported snippet in src/lib.rs using the linked Rust Playground, then trace how unreachable!() is expanded and checked in const functions. Done means the no-formatting invocation compiles like the analogous panic!() case, with regression coverage for the reported behavior.