Function rustc_const_eval::lookup_const_by_id

pub fn lookup_const_by_id<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId, substs: Option<&'tcx Substs<'tcx>>) -> Option<(&'tcx Expr, Option<Ty<'tcx>>)>

Unstable (rustc_private)

• def_id is the id of the constant.
• substs is the monomorphized substitutions for the expression.

substs is optional and is used for associated constants. This generally happens in late/trans const evaluation.