Function create_anon_const 

pub(crate) fn create_anon_const<'a, 'db>(
    interner: DbInterner<'db>,
    owner: ExpressionStoreOwnerId,
    store: &ExpressionStore,
    expr: ExprId,
    resolver: &Resolver<'db>,
    expected_ty: Ty<'db>,
    generics: &dyn Fn() -> &'a Generics<'db>,
    create_var: Option<&mut dyn FnMut(Span) -> Const<'db>>,
    lowering_mode: LoweringMode,
    forbid_params_after: Option<u32>,
) -> Result<Const<'db>, CreateConstError<'db>>