feat: add fallback field mapping for domain struct params

[kalbasit]

This adds multiple fallback strategies to map source struct fields to target struct
fields when field names differ between the wrapper API and the database adapter.
The strategies include: exact match, case-insensitive match, snake_case match,
and position-based match when structs have the same field count.

This is needed because sqlc generates different field names for unnamed query
parameters (e.g., LIMIT ? generates 'Limit' instead of 'BatchSize'). The fix enables
the generator to correctly map all parameters regardless of naming differences.

[kalbasit]

This change is part of the following stack:

• feat: add fallback field mapping for domain struct params #7 ◀

_{Change managed by git-spice.}

[gemini-code-assist]

Summary of Changes

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This pull request significantly improves the sqlc-multi-db generator's ability to map struct fields between different layers of an application. It introduces sophisticated fallback strategies to handle discrepancies in field names that arise when sqlc generates code for various database adapters, such as the issue with MySQL's LIMIT parameter. This ensures that the generator can correctly map all parameters regardless of naming differences, enhancing the robustness and flexibility of the generated code.

Highlights

• Enhanced Field Mapping Logic: Implemented multiple fallback strategies (exact, case-insensitive, snake_case, and position-based) to correctly map source struct fields to target struct fields even when names differ between the wrapper API and the database adapter.
• New Helper Functions: Introduced findSourceField, fieldsCompatible, and normalizeType to support the advanced field mapping and type compatibility checks, ensuring robust type comparison and normalization.
• Regression Test Added: A new test case, TestJoinParamsCallFieldMapping, was added to validate the improved field mapping, specifically addressing the MySQL LIMIT parameter naming discrepancy where sqlc generates different field names.

Changelog

• generator/constants.go
  • Added typeInt and typeBytes constants.
• generator/generator_test.go
  • Added TestJoinParamsCallFieldMapping to verify the new field mapping logic.
• generator/helpers.go
  • Implemented findSourceField, fieldsCompatible, and normalizeType functions.
  • Updated joinDomainStructParam to utilize the new field mapping strategies and handle package prefixes for target structs.

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[gemini-code-assist]

Code Review

This pull request introduces several fallback strategies for mapping struct fields between the domain and database layers, which is a valuable enhancement for handling inconsistencies in sqlc's generated code. The implementation adds name-based (exact, case-insensitive, snake_case) and position-based matching. I've found a potential issue in the mapping logic where a single source field could be mapped to multiple target fields, and I've provided a suggestion to ensure a one-to-one mapping.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 58.18182% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.21%. Comparing base (4b21a04) to head (8beb086).

Files with missing lines	Patch %	Lines
generator/helpers.go	58.18%	17 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   26.43%   29.21%   +2.77%     
==========================================
  Files           6        6              
  Lines         643      688      +45     
==========================================
+ Hits          170      201      +31     
- Misses        468      476       +8     
- Partials        5       11       +6     

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