LT01: Fix alias alignment with templates and add alignment_coordinate_space config

[jorenby]

Summary

Fixes alias alignment issues when using Jinja templating by implementing coordinate space selection logic that aligns based on source (visible) positions rather than rendered template positions. Also, adds alignment_coordinate_space config for manual override.

Resolves sqlfluff#5429

Key Changes:

• Added automatic detection of templated content to choose appropriate alignment coordinate space
• Implemented alignment_coordinate_space configuration parameter for manual override (:source or :templated)
• Enhanced alignment logic to handle mixed templated/non-templated content
• Added comprehensive test coverage for various Jinja templating scenarios

Problem

When using Jinja templates with alias alignment, SQLFluff would:

1. Flag LT01 errors even when aliases appear visually aligned
2. Apply fixes based on rendered macro results instead of visible template text
3. Push non-templated aliases excessively far to the right
4. Generate "line too long" violations (LT05)

Solution

The fix automatically detects templated content and switches to source-based coordinate alignment, ensuring aliases align based on what users see in their editor rather than the expanded macro results.

Test Plan

• All existing alignment tests pass
• New Jinja-specific alignment tests added and passing
• Edge cases handled (empty segments, mixed content, explicit overrides)
• Manual testing with dbt projects containing Jinja macros

Examples

Before (broken behavior):

select
    {{ generate_surrogate_key('test', ['a', 'b', 'c']) }} as test_key,
    b as b_col  -- LT01 error: claims aliases not aligned
from {{ ref("test") }}

After running sqlfluff fix, it would incorrectly produce something like:

select
    {{ generate_surrogate_key('test', ['a', 'b', 'c']) }} as test_key,
    b                                                                                                                                        as b_col  -- Excessive padding based on macro expansion
from {{ ref("test") }}

After (fixed behavior):

select
    {{ generate_surrogate_key('test', ['a', 'b', 'c']) }} as test_key,
    b                                                     as b_col  -- Properly aligned to visible template text
from {{ ref("test") }}

Credits

Initial implementation developed with assistance from GPT-5 in Cursor IDE. Code review, cleanup, and testing performed with Claude Code.

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]