Irmin_pack.LayoutSourceis_number is a less generic than Stdlib.int_of_string_opt. It matches this equivalent regex:
"([1-9][0-9]*|0)"
.
type classification = [ | `Branch| `Control| `Dict| `Gc_result of int| `Mapping of int| `Prefix of int| `Reachable of int| `Sorted of int| `Suffix of int| `V1_or_v2_pack ]val classification_t :
[ `Branch
| `Control
| `Dict
| `Gc_result of int
| `Mapping of int
| `Prefix of int
| `Reachable of int
| `Sorted of int
| `Suffix of int
| `V1_or_v2_pack ]
Irmin.Type.t