Inline const errors are opt-level-dependent

I tried this code:

fn inline_const() {
    const { panic!() }
}
pub fn main() {
    inline_const();
}

fn inline_const_with_const_generics_and_println<const N: i32>() {
    const { panic!() }
    println!();
}
pub fn main() {
    inline_const_with_const_generics_and_println::<0>();
}

fn inline_const_with_const_generics<const N: i32>() {
    const { panic!() }
}
pub fn main() {
    inline_const_with_const_generics::<0>();
}

fn inline_const_with_type_generics<T>() {
    const { panic!() }
}
pub fn main() {
    inline_const_with_type_generics::<i32>();
}

fn inline_const_with_const_generics_and_return<const N: i32>() -> Result<(), Box<dyn std::error::Error>> {
    const { panic!() }
    Ok(())
}
pub fn main() -> Result<(), Box<dyn std::error::Error>> {
    inline_const_with_const_generics_and_return::<0>()
}

I expected to see this happen:

The compile error should always occur, regardless of opt-level

error[E0080]: evaluation panicked: explicit panic
 --> repro.rs:3:13
  |
3 |     const { panic!() }
  |             ^^^^^^^^ evaluation of `inline_const::{constant#0}` failed here

note: erroneous constant encountered
 --> repro.rs:3:5
  |
3 |     const { panic!() }
  |     ^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0080`.

Instead, this happened:

rustc --edition 2024 -C opt-level=0 --crate-type lib --emit=obj -o out.o repro.rs
rustc --edition 2024 -C opt-level=1 --crate-type lib --emit=obj -o out.o repro.rs
rustc --edition 2024 -C opt-level=2 --crate-type lib --emit=obj -o out.o repro.rs
rustc --edition 2024 -C opt-level=3 --crate-type lib --emit=obj -o out.o repro.rs
rustc --edition 2024 -C opt-level=3 --crate-type bin --emit=obj -o out.o repro.rs
rustc +nightly --edition 2024 -C opt-level=3 -Z inline-mir=no --crate-type lib --emit=obj -o out.o repro.rs

Meta

rustc --version --verbose:

rustc 1.97.1 (8bab26f4f 2026-07-14)
binary: rustc
commit-hash: 8bab26f4f68e0e26f0bb7960be334d5b520ea452
commit-date: 2026-07-14
host: x86_64-pc-windows-msvc
release: 1.97.1
LLVM version: 22.1.6

The issue also reproduces with rustc 1.99.0-nightly (ad3d0bc14 2026-07-31).

Related

• https://github.com/rust-lang/rust/issues/107503
• https://github.com/rust-lang/rust/pull/122568

Note

While I used an LLM to investigate this issue and perform machine translation, I myself conducted the issue reproduction and original text creation, as required by the Rust LLM Usage Policy, which I note here.

Start by reproducing the supplied rustc commands across opt-levels, crate types, and -Z inline-mir=no, then compare the differing compilation paths. Read related issue #107503 and pull request #122568 for context. Done means every listed example consistently reports the inline-const panic instead of passing at optimization levels 2 and 3.