[BUG] BigQuery external table pseudo column causing "No column found" error

[the-kevin-kong]

Describe the bug
By default, BigQuery external tables come with a hidden _FILE_NAME pseudo column [docs] that returns the source file of the record. Since this is not part of the information schema, it triggers an error in dbt Fusion.

dbt0227: No column _FILE_NAME found.

What version of dbt Fusion is this bug in? (find out by running dbt --version)
dbt-fusion 2.0.0-preview.41

Is this a discrepancy between the dbt Fusion Engine and dbt Core? Check one.

• YES
• NO

To Reproduce

1. Create an external table in BigQuery

   CREATE EXTERNAL TABLE my_dataset.my_external_table (
       column1 STRING,
       column2 STRING,
       column3 STRING
   )
   OPTIONS (
       format = 'CSV',
       uris = ['gs://your-gcs-bucket/path/to/your/files/*'],
       field_delimiter = ',',
       skip_leading_rows = 1 -- If your CSV has a header row
   );

2. Create a model that queries the external table, including the _FILE_NAME pseudo column

   select _FILE_NAME from {{ source('my_dataset', 'my_external_table') }}

3. Run dbtf compile

Expected behavior
_FILE_NAME should be an acceptable field for external tables despite not being part of the information schema. Perhaps there can be an exception for _FILE_NAME when table_type = 'EXTERNAL'. Or a blanket exception for specific pseudo column fields.

Another pseudo column is _PARTITIONTIME which is used for partitioned tables. Similarly, Snowflake has METADATA columns.

Operating System and CPU Type (please complete the following information):

• Windows
• X86