Follow-on after [#25585](/github/pr-or-issue/oxc-project/oxc/25585).
Rename `options.sourceFileName` to `sourceFilename`. We use both capitalizations internal Rust code, but always `filename` in external JS APIs (Oxlint plugins etc).
NOTE: this is not marked as a breaking change as it was merged before the feature was released.
Follow-on after #25585.
Nit. Make `printSync` return an object with consistent shape. With `sourcemap: false` it now returns `{ code: string, map: null }` instead of just `{ code: string }`.
Co-authored-by: Cameron <cameron.clark@hey.com>
Follow-on after #25585.
Pure refactor. Re-order options so `sourcemap` is first. The other 2 are sourcemap-related, so it makes sense to have them after.
Follow-on after #25585.
Pure style change. Similar to #25848 - just remove the worst excesses of LLM coding style where it produces dense blocks of code with no line breaks, which makes code hard to read.
No substantive changes, just adds line breaks.
Follow-on after #25585.
Pure style change. I hate the way LLMs put line breaks in weird places like after "the" - it makes comments hard to read. And what's with all the colons and semicolons?
No substantive changes, just reformatting comments and docs to avoid this unreadable formatting.
## Summary
- throw a TypeError when indent is empty, contains characters other than spaces or tabs, or is not a string
- preserve the existing default tab indentation and unchanged printIndent hot path
- update API documentation and validation coverage
Pure refactor.
Move debug asserts that `code` cannot be an empty string into the body of `write` and `writeWithMap`. This makes it clearer what the invariants of these functions are.
Pure refactor. Move setting debug-only state to the end of `write*` functions, instead of start. This makes it clearer that it's setting up state for the _next_ call to reference.
`oxc-codegen`'s current API requires passing in a `SourceMapGenerator` as an option to generate source maps. This is currently really slow, and I imagine we'll want to generate source maps internally (perhaps in Rust), and return a source map string from `printSync` instead.
Alter `printSync`'s return type now, to support that without a breaking change later.
- Before: `function printSync(node: ESTree.Node, options?: Options): string`
- After: `function printSync(node: ESTree.Node, options?: Options): { code: string }`
Later on, it can return `{ code: string, map: string }` and that won't break existing users.
## 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.
## Summary
- Correct the binary-walk allocation claim: the implementation creates an initial visitor object and one for each nested left level.
- Retain and document the actual optimization: pending levels use `parent` links instead of a separate stack array.
## Summary
Validate `startingIndentLevel` before printing to prevent unbounded indentation-cache growth.
- Reject non-finite, fractional, negative, and unsafe integer values with a `RangeError`.
- Document the option as a non-negative integer.
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>
camc314