Reposition before recursion in fixes to avoid internal error

[alanmcruickshank]

This resolves #3656 .

The issue was caused by child segments trying to apply fixes to segments inserted or edited by a parent which hadn't yet assigned position markers using _position_segments. This simply adds an intermediate step after applying fixes to the parent where we optionally reposition self before applying fixes to children.

This will add a very slight performance overhead, but I don't think the fix routine is currently the bottleneck. Potentially in future we might be able to more selectively run this routine, but for now this feels ok. Added a test case too.

[tunetheweb]

Looks like a simple enough fix. But would be good if @barrywhart can review too.

[barrywhart]

Nice, elegant fix! My intuition was that we needed to do the positioning "top down", but there was a high risk I'd fumble around for a loonngg time working out the details.

Thanks!! 🙌

[barrywhart]

A dbt test is failing:

E               {% snapshot dim_aggregated_brand_hierarchy_snapshot %}
E               
E               {{
E                   config(
E                     strategy='check',
E                     unique_key='c1',
E                     target_schema='snapshots',
E                     check_cols='all'
E                   )
E               }}
E               
E             -     select c1
E             ?           ---
E             +     select
E             +         c1
E                   from
E                       foo
E               
E               {% endsnapshot %}

[alanmcruickshank]

A dbt test is failing:

Yeah I saw this, and I'm really not sure why 🤔 . I feel like I've uncovered a bigger bug.

[alanmcruickshank]

Ok, no I understand what's going on - by repositioning early - the matching of fixes to segments goes wrong. They no longer "find" their target because it's not the same segment. Will rethink approach.

[alanmcruickshank]

NOTE: This now includes the changes from #3661 to confirm that they solve the test fails I was otherwise getting. That will make the diff look weird but means we should merge the other PR first if all looks good.

[codecov]

Codecov Report

Merging #3658 (26c842c) into main (1977bc9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##             main     #3658   +/-   ##
========================================
  Coverage   99.99%   100.00%           
========================================
  Files         176       176           
  Lines       13348     13350    +2     
========================================
+ Hits        13347     13350    +3     
+ Misses          1         0    -1     

Impacted Files	Coverage Δ
src/sqlfluff/core/parser/segments/base.py	100.00% <100.00%> (ø)
src/sqlfluff/core/config.py	100.00% <0.00%> (+0.30%)	⬆️

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