Function rustc_mir_transform::mir_for_ctfe_of_const_arg

pub(crate) fn mir_for_ctfe_of_const_arg<'tcx>(
    tcx: TyCtxt<'tcx>,
    (did, param_did): (LocalDefId, DefId)
) -> &'tcx Body<'tcx>

Same as mir_for_ctfe, but used to get the MIR of a const generic parameter. The docs on WithOptConstParam explain this a bit more, but the TLDR is that we’d get cycle errors with mir_for_ctfe, because typeck would need to typeck the const parameter while type checking the main body, which in turn would try to type check the main body again.