…an (#24023)

## What

`update_generated_line_and_column` (in `oxc_codegen`'s sourcemap builder) scans every emitted byte once to track the generated line/column for source-map tokens. Profiling `Codegen::build` with source maps enabled shows it is the **single hottest function** (~20% of self-time) — it walks the output byte-by-byte with a `match` per byte.

The vast majority of output bytes are "boring": ASCII that is neither a line break nor part of a Unicode char, and that don't change the line count or the last-line ASCII flag. This skips runs of them **8 bytes at a time** with a branchless SWAR test — the classic zero-byte-in-a-word trick for `\n`/`\r` plus a high-bit test for non-ASCII — and only falls back to the (unchanged) per-byte logic at the interesting bytes.

## Why it's correct

The fast-forward **only advances the cursor**; it never mutates line/column/ASCII state. It skips exactly the bytes the old scalar path already handled with `idx += 1` and no state change, so it is a provably-equivalent transformation and the emitted source map is byte-identical.

- SWAR predicate exhaustively checked against a brute-force reference (a false positive only forces a harmless scalar fallback; false negatives — the dangerous case — are ruled out).
- New unit tests cover long lines, `\r\n` / lone `\r`, embedded Unicode (`Ö`), and U+2028, **including line breaks straddling the 8-byte word boundary**.
- Existing `sourcemap.rs` integration tests + the full `oxc_codegen` suite pass; no `unsafe`, all slice access bounds-guarded.

## Performance

Interleaved A/B (sourcemap-enabled codegen, median-of-medians):

| file | delta |
| --- | --- |
| binder.ts | ~-4.5% |
| react.development.js | ~-2% |
| App.tsx | ~-1 to -3% |
| kitchen-sink.tsx (short-token synthetic) | ~flat |

The win scales with the amount of long string/comment/line content (≥8 boring bytes per run); there is no effect when source maps are disabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

…an (#24023)

## What

`update_generated_line_and_column` (in `oxc_codegen`'s sourcemap builder) scans every emitted byte once to track the generated line/column for source-map tokens. Profiling `Codegen::build` with source maps enabled shows it is the **single hottest function** (~20% of self-time) — it walks the output byte-by-byte with a `match` per byte.

The vast majority of output bytes are "boring": ASCII that is neither a line break nor part of a Unicode char, and that don't change the line count or the last-line ASCII flag. This skips runs of them **8 bytes at a time** with a branchless SWAR test — the classic zero-byte-in-a-word trick for `\n`/`\r` plus a high-bit test for non-ASCII — and only falls back to the (unchanged) per-byte logic at the interesting bytes.

## Why it's correct

The fast-forward **only advances the cursor**; it never mutates line/column/ASCII state. It skips exactly the bytes the old scalar path already handled with `idx += 1` and no state change, so it is a provably-equivalent transformation and the emitted source map is byte-identical.

- SWAR predicate exhaustively checked against a brute-force reference (a false positive only forces a harmless scalar fallback; false negatives — the dangerous case — are ruled out).
- New unit tests cover long lines, `\r\n` / lone `\r`, embedded Unicode (`Ö`), and U+2028, **including line breaks straddling the 8-byte word boundary**.
- Existing `sourcemap.rs` integration tests + the full `oxc_codegen` suite pass; no `unsafe`, all slice access bounds-guarded.

## Performance

Interleaved A/B (sourcemap-enabled codegen, median-of-medians):

| file | delta |
| --- | --- |
| binder.ts | ~-4.5% |
| react.development.js | ~-2% |
| App.tsx | ~-1 to -3% |
| kitchen-sink.tsx (short-token synthetic) | ~flat |

The win scales with the amount of long string/comment/line content (≥8 boring bytes per run); there is no effect when source maps are disabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

### 🚀 Features

- 260425f semantic/examples: Include unresolved references (#24214)
(camc314)
- 2d9b0b3 minifier: Fold boolean-literal ternary branches in value
contexts (#24110) (Dunqing)
- 61fbf10 ast: Implement `ReplaceWith` on all AST types (#24013)
(overlookmotel)
- 7db7a29 allocator: Add `ReplaceWith` trait (#24012) (overlookmotel)
- 4eb074e mangler: Add `reserved` option for names that must not be
mangled (#24041) (Dunqing)
- 2e62012 data_structures: Add `StringExt` trait (#24006)
(overlookmotel)
- 60e7160 minifier: Drop side-effect-free IIFEs whose result is unused
(#23967) (Dunqing)
- 26dd9e2 ast: Add method to widen inherited enum ref to parent ref
(#23961) (overlookmotel)

### 🐛 Bug Fixes

- e8b50ee transformer: Clean up semantics for stripped TypeScript syntax
(#24180) (camc314)
- d966d0b react_compiler: Remove clippy allows (#24168) (Boshen)
- 854ef8d react_compiler: Compile generic functions instead of
over-bailing on type-param hoisting (#24158) (Boshen)
- 093586c react_compiler: Align memoization cache-slot allocation with
Babel (#24157) (Boshen)
- 09c8f59 react_compiler: Normalize snapshot fixture paths (#24142)
(camc314)
- f13df97 react_compiler: Drop stray empty statement from catch bindings
(#24133) (Boshen)
- cb2a505 react_compiler: Codegen destructuring reassignment targets
(#24131) (Boshen)
- b82c394 react_compiler: Propagate codegen invariants instead of
emitting empty bodies (#24128) (Boshen)
- 5771982 react_compiler: Render unchanged programs as source in fixture
snapshots (#24129) (Boshen)
- 4b16e1a transformer/async-to-generator: Preserve direct eval scope
flags (#24136) (camc314)
- 4e9194f react_compiler: Lower `delete obj.prop` to
Property/ComputedDelete (#24123) (Boshen)
- 0b25582 ast: Type binding node `typeAnnotation` as `TSTypeAnnotation |
null` (#23113) (Boshen)
- 018c0e5 transformer: Hoist lowered async declarations (#22770)
(camc314)
- 652fbaf mangler: Keep names of destructured exported bindings (#24036)
(Dunqing)
- e274415 minifier: Don't drop global calls that throw despite pure
arguments (#23917) (Dunqing)
- 59abb30 minifier: Only merge string literals in `try_fold_add` when
the inner operator is `+` (#23622) (Jerry Zhao)

### ⚡ Performance

- c5ca77b transformer: Avoid cloning refresh options (#24191) (camc314)
- bf1a151 react_compiler: Compile out debug printers (#24184) (Boshen)
- abb44a0 transformer: Build fixed object-rest arguments (#24190)
(camc314)
- a4db731 isolated_declarations: Use `ReplaceWith` instead of `TakeIn`
(#24016) (overlookmotel)
- ff10855 transformer: Use `ReplaceWith` instead of `TakeIn` (#24015)
(overlookmotel)
- bd49aff ecmascript: Avoid heap-allocating Math.min/max/imul operands
(#23941) (Lawrence Lin)
- e4b708b react_compiler: Skip compiled files before prefilters (#24171)
(Boshen)
- c59f2fe rust: Return impl ExactSizeIterator from slice-backed
accessors (#24144) (Boshen)
- 5d6d04a codegen: SWAR-skip boring byte runs in sourcemap line/column
scan (#24023) (Boshen)
- a55e0be traverse: Reduce string operations in `get_var_name_from_node`
(#24007) (overlookmotel)
- e6d48e1 transformer/nullish_coalescing: Move cold path into separate
function (#23989) (overlookmotel)
- c4e35b5 transformer/object_rest_spread: Pre-allocate capacity in `Vec`
(#23988) (overlookmotel)
- 527b8e5 transformer/decorators: Narrow type earlier (#23987)
(overlookmotel)

### 📚 Documentation

- 30d17f5 allocator: Clarify docs for `TakeIn::take_in_box` (#24093)
(overlookmotel)
- 675e6a8 ast: Correct doc comment for `PrivateFieldExpression` (#24008)
(overlookmotel)
- e4c30e6 minifier: Explain what `dce` mode means (#23994) (Dunqing)
- 37cbf88 ast_macros: Document fields of `StructDetails` (#23959)
(overlookmotel)
- 4de3e54 ast: Correct doc comment (#23948) (overlookmotel)

Co-authored-by: Boshen <[email protected]>