23099652318
94%

Ran 15 Mar 2026 12:28AM UTC

Jobs 1

Files 54

Run time 1min

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Committed 12 Mar 2026 08:33PM UTC coverage: 95.976% (-0.7%) from 96.628%

Build # 23099652318

Build Type

push

github

Committed by

web-flow

Commit Message

Optimize LineScanner newline detection and fix backwards position bug (#2342)

- Replaced RegExp reliance in `LineScanner` (such as `_newlinesIn`) with manual code unit iteration to avoid unnecessary allocations and scanning overhead.
- Improved performance in core loop methods (`readChar`, `scanChar`, `scan`) which directly cascades to `SpanScanner`.
- Fixed a `RangeError` bug when setting `position` backwards across a `\r\n` boundary by completely rewriting the bounded boundary-checking loop.
- Added a benchmark script to measure raw throughput improvements.
- Added comprehensive test coverage in `line_scanner_test.dart` for backwards boundary traversal.

### Performance Comparison

| Benchmark Target | Before (us) | After (us) | Change (%) | Status |
| :--- | :--- | :--- | :--- | :--- |
| **StringScanner readChar** | 16,790 | 16,430 | -2.1% | Minor Improv. |
| **LineScanner readChar** | 57,328 | 55,491 | -3.2% | Minor Improv. |
| **SpanScanner readChar** | 49,400 | 50,158 | +1.5% | Slight Regression |
| **StringScanner scan** | 1,103,350 | 1,102,107 | -0.1% | Negligible |
| **LineScanner scan** | 2,185,230 | 1,338,592 | **-38.7%** | **Major Win** |
| **SpanScanner scan** | 1,209,363 | 1,198,558 | -0.9% | Minor Improv. |

Run Details

1574 of 1640 relevant lines covered (95.98%)

3.67 hits per line

Jobs

ID	Job ID	Ran	Files	Coverage
1	23099652318.1	15 Mar 2026 12:28AM UTC	54	95.98	GitHub Action Run

dart-lang / tools / 23099652318
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