Unexpected exception: tuple index out of range (L019)

Expected Behaviour

Including configuration

[sqlfluff:rules:L019]
comma_style = leading

does not lead to critical exception.

Observed Behaviour

Running sqlfluff lint models/dwh/best_model.sql with the config below causes exception.

(venv) ➜  ✗ sqlfluff lint models/dwh/best_model.sql
CRITICAL   [L019] Applying rule L019 threw an Exception: tuple index out of range
Traceback (most recent call last):
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/base.py", line 282, in crawl
    res = self._eval(
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/std.py", line 2218, in _eval
    last_seg = self._last_code_seg(raw_stack)
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/std.py", line 2133, in _last_code_seg
    if raw_stack[idx].is_code or raw_stack[idx].is_type("newline"):
IndexError: tuple index out of range
CRITICAL   [L019] Applying rule L019 threw an Exception: tuple index out of range
Traceback (most recent call last):
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/base.py", line 282, in crawl
    res = self._eval(
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/std.py", line 2218, in _eval
    last_seg = self._last_code_seg(raw_stack)
  File "/Users/justinwagg/Documents/data/venv/lib/python3.8/site-packages/sqlfluff/core/rules/std.py", line 2133, in _last_code_seg
    if raw_stack[idx].is_code or raw_stack[idx].is_type("newline"):
IndexError: tuple index out of range
== [models/dwh/best_model.sql] FAIL
L:   1 | P:   1 | L019 | Unexpected exception: tuple index out of range; Could
                       | you open an issue at
                       | https://github.com/sqlfluff/sqlfluff/issues ? You can
                       | ignore this exception for now, by adding '--noqa: L019'
                       | at the end of line 1
L:   2 | P:   1 | L019 | Unexpected exception: tuple index out of range; Could
                       | you open an issue at
                       | https://github.com/sqlfluff/sqlfluff/issues ? You can
                       | ignore this exception for now, by adding '--noqa: L019'
                       | at the end of line 2
L:   4 | P:   1 | L003 | Indent expected and not found compared to line #3
L:   5 | P:   1 | L003 | Indent expected and not found compared to line #3

Removing

[sqlfluff:rules:L019]
comma_style = leading

fixes the issue.

Steps to Reproduce

Model:

-- models/dwh/best_model.sql
{{
  config(
    materialized='incremental',
    unique_key='field_1'
  )
}}

select field_1
,field_2
,field_3
from my_great_table

(venv) ➜ ✗ sqlfluff lint models/dwh/best_model.sql

Version

Include the output of sqlfluff --version along with your Python version

(venv) ➜ ✗ python -V
Python 3.8.0
(venv) ➜ ✗ sqlfluff --version
sqlfluff, version 0.4.0a3

Configuration

[sqlfluff]
templater = dbt
dialect = bigquery
exclude_rules = L036,L009,L008

[sqlfluff:indentation]
indented_joins = False

[sqlfluff:rules:L019]
comma_style = leading

[sqlfluff:rules:L003]
lint_templated_tokens = False

[NiallRees]

sqlfluff, version 0.3.6

OK cool. The part that’s failing in your stack trace has been totally changed in 0.4.0 - can you try it with 0.4.0a3?

[MinchoG]

Oh LOL

==== fixing violations ====
1983 fixable linting violations found
Are you sure you wish to attempt to fix these? [Y/n] ...
Attempting fixes...
Persisting Changes...
== [5_WAREHOUSE/F_MIXPANEL_EVENTS.sql] PASS
Done. Please check your files to confirm.

Thanks a bunch!!!