Feature: Baseline file support for gradual adoption

[kojiromike]

When introducing sqruff to an existing codebase, there are often many pre-existing lint errors. Requiring all errors to be fixed before CI can pass creates a high barrier to adoption.

Prior art

Several popular linters have implemented baseline functionality:

• PHPStan (PHP) - phpstan analyse --generate-baseline creates phpstan-baseline.neon
• Psalm (PHP) - psalm --set-baseline=psalm-baseline.xml creates XML baseline
• RuboCop (Ruby) - rubocop --auto-gen-config creates .rubocop_todo.yml
• Ruff (Python, also Rust-based) - supports --baseline flag
• ESLint (JavaScript) - feature request #13437; third-party solutions like eslint-baseline exist
• SARB - generic Static Analysis Results Baseliner that works with multiple tools

Notably, SQLFluff (the Python linter sqruff is based on) does not have native baseline support, relying instead on -- noqa comments or downgrading rules to warnings. Native baseline support would be a differentiating feature for sqruff.

Since sqruff and Ruff are both Rust-based linters, Ruff's approach may (or may not) translate well to sqruff.

Benefits

• Lower barrier to adoption for existing projects
• Enables incremental improvement
• Prevents regressions while allowing legacy issues to be addressed over time

[benfdking]

Sounds like a good idea! Thanks for the suggestion!