Wrong sql when adding a time interval to a date.

[jcmincke]

import ibis
import ibis_bigquery
from google.cloud import bigquery
import pandas as pd
import datetime as dt

my_table = 'my_table'

pdf = pd.DataFrame({'date': [dt.date(2020, 1, 1), dt.date(2021, 5, 15), dt.date(2021, 7, 9)]})

# Load client
client = bigquery.Client(project=my_project)

# Load data to BQ
client.delete_table(my_dataset + "." + my_table, not_found_ok=True)
job = client.load_table_from_dataframe(pdf, my_dataset + "." + my_table)

ibis.options.interactive = False

conn = ibis_bigquery.connect(
    project_id=my_project,
    dataset_id=my_dataset)

t = conn.table(my_table)

delta = dt.timedelta(days=6)

e1 = t.mutate(z=t.date + ibis.literal(delta))

print(ibis.bigquery.compile(e1))

"""
SELECT *, DATE_ADD(`date`, INTERVAL 6 days, 0:00:00 DAY) AS `z` FROM ...
"""

e1.execute()

And the exception is:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis/expr/types.py", line 223, in execute
    return execute(
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis/client.py", line 382, in execute
    return backend.execute(
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis/client.py", line 222, in execute
    result = self._execute_query(query, **kwargs)
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis/client.py", line 229, in _execute_query
    return query.execute()
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis_bigquery/client.py", line 196, in execute
    with self.client._execute(
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/ibis_bigquery/client.py", line 482, in _execute
    query.result()  # blocks until finished
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/google/cloud/bigquery/job/query.py", line 1266, in result
    super(QueryJob, self).result(retry=retry, timeout=timeout)
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/google/cloud/bigquery/job/base.py", line 679, in result
    return super(_AsyncJob, self).result(timeout=timeout, **kwargs)
  File "/Users/V3/windev/carrefour/gcp/venv/lib/python3.9/site-packages/google/api_core/future/polling.py", line 134, in result
    raise self._exception
google.api_core.exceptions.BadRequest: 400 Syntax error: Expected ")" but got ":" at [1:46]
(job ID: adf6f6be-fbf2-485f-ad6c-e651ab84d978)
                  -----Query Job SQL Follows-----                   
    |    .    |    .    |    .    |    .    |    .    |    .    |
   1:SELECT *, DATE_ADD(`date`, INTERVAL 6 days, 0:00:00 DAY) AS `z`
   2:FROM ....
   3:LIMIT 10000
    |    .    |    .    |    .    |    .    |    .    |    .    |