My comments:
* I miss in documentation description of implementation - its is based on binary searching, and when second parameter is unsorted array, then it returns some nonsense without any warning.
* Description for anyelement is buggy twice times
"varwidth_bucket(5.35::numeric, ARRAY[1, 3, 4, 6]::numeric)"
probably should be "varwidth_bucket(5.35::numeric, ARRAY[1, 3, 4, 6]::numeric[])"
BUT it is converted to double precision, function with polymorphic parameters is not used. So it not respects a widh_buckets model:
postgres=# \dfS width_bucket
List of functions
Schema │ Name │ Result data type │ Argument data types │ Type
────────────┼──────────────┼──────────────────┼───────────────────────────────────────────────────────────────┼────────
pg_catalog │ width_bucket │ integer │ double precision, double precision, double precision, integer │ normal
pg_catalog │ width_bucket │ integer │ numeric, numeric, numeric, integer │ normal
(2 rows)
There should be a interface for numeric type too. I am sure so important part of code for polymorphic type can be shared.
Regards
Pavel