update_spec and create_table accept two partition fields with the same name #4304

Apache Iceberg version

main (development)

Please describe the bug 🐞

validate_partition_name in pyiceberg/partitioning.py is meant to reject empty and duplicate partition field names (Partition name has to be unique: ...), but it returns early when the name is not also a schema column, so those checks only run for names that match a column. As a result update_spec() can commit a spec with two fields of the same name, for example through rename_field. create_table does not check uniqueness at all, because assign_fresh_partition_spec_ids passes a fresh set of names for every field.

from pyiceberg.catalog.sql import SqlCatalog
from pyiceberg.schema import Schema
from pyiceberg.transforms import BucketTransform
from pyiceberg.types import LongType, NestedField

catalog = SqlCatalog("default", uri="sqlite:///:memory:", warehouse="file:///tmp/warehouse")
catalog.create_namespace("db")
schema = Schema(NestedField(1, "x", LongType()), NestedField(2, "y", LongType()))
table = catalog.create_table("db.events", schema)

with table.update_spec() as update:
    update.add_field("x", BucketTransform(16), "x_bucket")
    update.add_field("y", BucketTransform(16), "y_bucket")

with table.update_spec() as update:
    update.rename_field("x_bucket", "y_bucket")  # accepted

print(table.spec())

Output on main:

[
  1000: y_bucket: bucket[16](1)
  1001: y_bucket: bucket[16](2)
]

Expected: ValueError: Partition name has to be unique: y_bucket, as when the name matches a schema column.

Willingness to contribute

• I can contribute a fix for this bug independently