Internal error on fixing L032

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What Happened

sqlfluff fix x.sql --dialect=mysql --rules=L032 causes internal error, where x.sql has following contents:

select c1.Name, c2.Name, c5.Name from city as c1
inner join city as c2 using (ID)
inner join (
  select c3.ID, c4.Name from city as c3
  inner join city as c4 using (ID)
  ) as c5
  on c1.ID = c5.ID
  limit 3;

This is a valid query and works fine with the world database in MySQL Example Databases (https://dev.mysql.com/doc/index-other.html)

mysql> select c1.Name, c2.Name, c5.Name from city as c1
    -> inner join city as c2 using (ID)
    -> inner join (
    ->   select c3.ID, c4.Name from city as c3
    ->   inner join city as c4 using (ID)
    ->   ) as c5
    ->   on c1.ID = c5.ID
    ->   limit 3;
+----------+----------+----------+
| Name     | Name     | Name     |
+----------+----------+----------+
| Kabul    | Kabul    | Kabul    |
| Qandahar | Qandahar | Qandahar |
| Herat    | Herat    | Herat    |
+----------+----------+----------+
3 rows in set (0.00 sec)

Expected Behaviour

success without internal error

Observed Behaviour

internal error occurred

(sqlfluff) ~/prog/python-study/sqlfluff% sqlfluff fix x.sql --dialect=mysql --rules=L032
==== finding fixable violations ====
WARNING    SEG: (<CodeSegment: (None) 'c1'>, <SymbolSegment: (None) '.'>, <CodeSegment: (None) 'ID'>), POS: None
WARNING    Unable to lint x.sql due to an internal error. Please report this as an issue with your query's contents and stacktrace below!
To hide this warning, add the failing file to .sqlfluffignore
Traceback (most recent call last):
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/linter/runner.py", line 103, in run
    yield partial()
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/linter/linter.py", line 741, in lint_rendered
    return cls.lint_parsed(
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/linter/linter.py", line 667, in lint_parsed
    tree, initial_linting_errors, ignore_buff = cls.lint_fix_parsed(
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/linter/linter.py", line 586, in lint_fix_parsed
    new_tree, _, _ = tree.apply_fixes(
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/parser/segments/base.py", line 1278, in apply_fixes
    s, before, after = seg.apply_fixes(dialect, rule_code, fixes)
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/parser/segments/base.py", line 1278, in apply_fixes
    s, before, after = seg.apply_fixes(dialect, rule_code, fixes)
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/parser/segments/base.py", line 1278, in apply_fixes
    s, before, after = seg.apply_fixes(dialect, rule_code, fixes)
  [Previous line repeated 3 more times]
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/parser/segments/base.py", line 1331, in apply_fixes
    segments=self._position_segments(
  File "/Users/yoichi/.virtualenvs/sqlfluff/lib/python3.10/site-packages/sqlfluff/core/parser/segments/base.py", line 549, in _position_segments
    raise ValueError("Unable to find working position.")
ValueError: Unable to find working position.

==== no fixable linting violations found ====
All Finished 📜 🎉!

How to reproduce

sqlfluff fix x.sql --dialect=mysql --rules=L032

Dialect

MySQL

Version

sqlfluff, version 1.2.1 Python 3.10.0

Configuration

not using configuration file

Are you willing to work on and submit a PR to address the issue?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project’s Code of Conduct

[alanmcruickshank]

Found a fairly simple solution, PR is live and ready for review.

[alanmcruickshank]

ok, I think I know what’s going on here:

• Fixes strip position markers from new segments so the can be effectively repositioned.
• Fixes are applied recursively in the order: fix self, fix children, …, reposition children, reposition self.
• In this case I’m pretty sure that we’re applying fixes to a segment and it’s children, and when we try to reposition the child, we get an exception because the parent segment doesn’t have a functioning position to use.

This should be solvable by passing the child at least a partially useful position to work with. I’ll work on a fix.