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Reduce formatter source-slice overhead - #29855
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Summary
Compile the formatter's newline-check helper and its calls only when debug assertions are enabled, eliminating an unnecessary source-slice read in release builds. Inline source-slice access so callers can optimize the remaining reads, and use
track_callerto report the failing debug check's call site.Local Apple silicon measurements of formatting and printing pre-parsed files used 1.61% fewer retired instructions across the five Ruff formatter benchmark inputs and 1.18% fewer across ten Python standard-library files, compared with
08aac42edb. Elapsed-time differences were within measurement noise.Test Plan
The formatter tests and Clippy pass, and formatted text and source maps match the base revision.