Pure refactor. Move the category consts (`CAT_IDENT` etc) into a separate file.
2 reasons:
1. `write.ts` had got too large.
2. `index.ts`, which is not part of printer builds, imports `CAT_OTHER`. Importing it from a file containing only consts avoids any problems with minifier not being able to recognise dead code and remove it.
Optimization to sourcemap builds. This is what the rest of this stack has been working towards.
All the `writeWithMap*` and `markMap*` functions received a `node` param which they're extract `start` and `end` from. The problem is that these functions receive a range of different node types, so accessing `node.start` / `node.end` are megamorphic, involving an expensive dispatch.
Instead, extract `start` and `end` at call sites, where the type of `node` is already known (monomorphic), and pass them in to `writeWithMap*` / `markMap*` functions.
These functions still keep their `node` param, as it's needed for debug asserts, but it's never touched in release builds. #25989 removes it entirely from release builds too.
This has quite a large effect on perf. The cumulative perf gain of this stack (#25968 onwards) in the "without generation" sourcemaps benchmark is:
<table>
<tr>
<th align="left">Fixture</th>
<th align="right">Bytes</th>
<th align="right">Before</th>
<th align="right">After</th>
<th align="right">Faster by</th>
</tr>
<tr>
<td align="left">
`RadixUIAdoptionSection.jsx`
</td>
<td align="right">2,518</td>
<td align="right">0.0077 ms</td>
<td align="right">0.0059 ms</td>
<td align="right">+31.5%</td>
</tr>
<tr>
<td align="left">
`react.development.js`
</td>
<td align="right">72,141</td>
<td align="right">0.2549 ms</td>
<td align="right">0.2015 ms</td>
<td align="right">+26.9%</td>
</tr>
<tr>
<td align="left">
`lodash.js`
</td>
<td align="right">544,096</td>
<td align="right">1.14 ms</td>
<td align="right">0.9289 ms</td>
<td align="right">+23.5%</td>
</tr>
<tr>
<td align="left">
`App.tsx`
</td>
<td align="right">415,340</td>
<td align="right">1.84 ms</td>
<td align="right">1.51 ms</td>
<td align="right">+21.2%</td>
</tr>
<tr>
<td align="left">
`binder.ts`
</td>
<td align="right">193,077</td>
<td align="right">0.6598 ms</td>
<td align="right">0.5483 ms</td>
<td align="right">+20.6%</td>
</tr>
<tr>
<td align="left">
`kitchen-sink.tsx`
</td>
<td align="right">732,222</td>
<td align="right">5.12 ms</td>
<td align="right">4.33 ms</td>
<td align="right">+17.7%</td>
</tr>
<tr>
<td align="left">
`antd.js`
</td>
<td align="right">6,683,633</td>
<td align="right">23.52 ms</td>
<td align="right">20.30 ms</td>
<td align="right">+15.7%</td>
</tr>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</table>
The vast majority of that gain is down to this PR, and the ones preceding it which also remove polymorphic/megamorphic accesses.
---
Note: Actually this change is unnecessary for `writeWithMapNamed`, `writeWithMapNamedPrivate`, and `writeWithMapNamedJSXNoLast` - they only receive a single type of node so are already monomorphic. But it's easier to be consistent, and this uniformity enables the further optimization in #25989. We could pare this back in a later PR, so we only pass in `start` and `end` where it's beneficial to do so.
Small optimization to sourcemap builds.
Add functions for writing with a source mapping, where it's known from what's being written that the mapping cannot need a name, because `node.name` is never a string, and change all call sites to use the appropriate function.
This allows removing 2 checks from ``recordSourceMapping``:
- `typeof node.name === "string"` - because that's now statically known.
- `printedName.length > 0` - because identifiers cannot be length.
All `write` and `markMap` functions take a `NamedMappableNode` or `UnnamedMappableNode`, which makes it a type error to call the wrong function.
`markMapNamed` becomes dead code, and is removed.
Pure refactor. Just rename functions:
- `markWithMap` -> `markMap` for brevity.
- All functions which can produce a named mapping called `*Named`.
This mainly prepares the way for next PR #25975, which introduces separate `write` functions for where a mapping can never be named.
## Summary
- Detect actual case-insensitive `</script` sequences in the initial string-escape scan.
- Keep strings containing only harmless `<` on the bulk-write fast path.
- Add regression coverage for script closers, controls, paired and lone surrogates, and template quasis.
## Benchmark methodology
No permanent microbenchmark is added. Measurements used release bundles built with `pnpm --filter oxc-codegen run build` on Node v26.5.0, a one-off focused harness over representative string-literal ASTs, and the existing `packages/codegen/bench.bench.ts` parsed-AST fixtures. The focused harness used ten warmup batches and 20 measured batches per case; Vitest fixtures used 1s warmup and 3s measurement windows (50/20 iteration minima).
The removed one-off harness is retained for reference at [bench.string.bench.ts](https://github.com/oxc-project/oxc/blob/49e7a9d43bdc55a8f01075363bb8701ca5a9380c/packages/codegen/bench.string.bench.ts).
Focused release results (ms/print, mean ± standard deviation):
| Case | Before | After | Change |
| --- | ---: | ---: | ---: |
| Short ordinary string | 0.00003 ± 0.00000 | 0.00003 ± 0.00000 | no material change |
| Long string without `<` | 0.02048 ± 0.00114 | 0.01906 ± 0.00038 | within noise / slightly faster |
| Dense harmless HTML/SVG-like `<` (15,360 chars) | 0.05625 ± 0.00152 | 0.01283 ± 0.00036 | 77% faster |
| Mixed text with harmless `<` | 0.04766 ± 0.00210 | 0.02371 ± 0.00072 | 50% faster |
| Frequent mixed-case `</script` closers | 0.04350 ± 0.00074 | 0.04366 ± 0.00079 | within noise |
Existing parsed-AST benchmark fixtures (Vitest RME 0.15–0.79%): Radix 0.0028 -> 0.0027 ms, React development 0.0981 -> 0.0976 ms. App.tsx varied from 0.6261 to 0.6657 ms after versus 0.6415 ms before, so this PR makes no throughput claim for that fixture and shows no consistent regression.
A release CPU profile of the dense harmless case reduced `printEscapedStringContents` from 1,099 of 1,459 samples, plus 124 `^</script` regex samples, to zero; the after profile spends 321 of 383 samples in the single initial scan.
Add `oxc-codegen` package - a printer written in TS.
### Features
- Prints JS, JSX, TS, TSX.
- Matches `oxc_codegen` exactly on all Test262, TypeScript, Acorn-JSX fixtures.
- Very fast.
### Deficiencies
- Pretty-printing only (no compact/minified output).
- No support for printing comments.
- Source map support is semi-there, but largely untested, and poor API (design doc has some ideas on how to improve it).
### This PR adds
- The printer code.
- Conformance testing infra.
- Further tests for edge cases.
- README.
- Design doc - how it differs from `oxc_codegen` and why, what produces the perf.
### This PR doesn't add
- Not integrated into CI or release pipeline.
### Notes
This started as a slop port of `oxc_codegen`. I've iterated on that base, cleaned it up a lot, and at least skimmed through all of it. I think it's in fairly decent shape.
The design doc is I think worth a read. It explains the rationale for the choices, in particular the "1 codebase, 4 builds" approach.
I've put it in a new top-level directory called `packages`. It's not an app, so didn't seem to me to fit alongside `apps/oxlint` and `apps/oxfmt`. It's pure JS, so not like e.g. `napi/parser`. And it felt too heavyweight to put into `npm` dir. But maybe there's a better place for it.
Co-authored-by: Cameron <cameron.clark@hey.com>
overlookmotel