CFI typeid encode_ty todo! ICE on ty::UnsafeBinder

[SebTardif]

Summary

compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs encode_ty has todo!() on ty::UnsafeBinder(_). If LLVM CFI / KCFI type metadata is requested for a function whose signature mentions an unstable unsafe-binder type, rustc ICEs instead of emitting a typeid.

Unsafe binders are transparent at the type level for most queries; encoding the region-erased inner type is consistent with symbol mangling (v0 / PR #581 pattern) and other UnsafeBinder arms.

Origin

Audit of incomplete TyKind / UnsafeBinder match arms in the compiler, SebTardif/rust fork of rust-lang/rust.

Affected code (upstream tip at audit time)

https://github.com/rust-lang/rust/blob/f28ac764c36/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs#L595-L598

// FIXME(unsafe_binders): Implement this.
ty::UnsafeBinder(_) => {
    todo!()
}

Suggested fix

ty::UnsafeBinder(bound_ty) => {
    let inner = tcx.instantiate_bound_regions_with_erased((*bound_ty).into());
    typeid.push_str(&encode_ty(tcx, inner, dict, options));
}

Impact

Low-to-medium, gated on unstable unsafe_binders plus CFI/KCFI sanitizer builds. Without the feature, this arm is unreachable in practice. With it, ICE is a hard failure for affected crates.

Related

• symbol_mangling v0: todo! ICE on ty::UnsafeBinder #579 (symbol_mangling v0 UnsafeBinder)
• tech-debt: remaining UnsafeBinder todo!/FIXME cluster (const_eval, mangling, rustc_public) #567 (UnsafeBinder todo cluster)
• symbol_mangling: mangle UnsafeBinder via erased inner type #581 (symbol_mangling fix PR)