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Jarred Sumner 86d4d87beb feat(unicode): migrate grapheme breaking to uucode with GB9c support (#26376) 
## Summary

Replace Bun's outdated grapheme breaking implementation with [Ghostty's
approach](https://github.com/ghostty-org/ghostty/tree/main/src/unicode)
using the [uucode](https://github.com/jacobsandlund/uucode) library.
This adds proper **GB9c (Indic Conjunct Break)** support — Devanagari
and other Indic script conjuncts now correctly form single grapheme
clusters.

## Motivation

The previous implementation used a `GraphemeBoundaryClass` enum with
only 12 values and a 2-bit `BreakState` (just `extended_pictographic`
and `regional_indicator` flags). It had no support for Unicode's GB9c
rule, meaning Indic conjunct sequences (consonant + virama + consonant)
were incorrectly split into multiple grapheme clusters.

## Architecture

### Runtime (zero uucode dependency, two table lookups)

```
codepoint → [3-level LUT] → GraphemeBreakNoControl enum (u5, 17 values)
(state, gb1, gb2) → [8KB precomputed array] → (break_result, new_state)
```

The full grapheme break algorithm (GB6-GB13, GB9c, GB11, GB999) runs
only at **comptime** to populate the 8KB decision array. At runtime it's
pure table lookups.

### File Layout

```
src/deps/uucode/              ← Vendored library (MIT, build-time only)
src/unicode/uucode/           ← Build-time integration
  ├── uucode_config.zig       ← What Unicode properties to generate
  ├── grapheme_gen.zig        ← Generator: queries uucode → writes tables
  ├── lut.zig                 ← 3-level lookup table generator
  └── CLAUDE.md               ← Maintenance docs
src/string/immutable/         ← Runtime (no uucode dependency)
  ├── grapheme.zig            ← Grapheme break API + comptime decisions
  ├── grapheme_tables.zig     ← Pre-generated tables (committed, ~91KB source)
  └── visible.zig             ← Width calculation (2 lines changed)
scripts/update-uucode.sh      ← Update vendored uucode + regenerate
```

### Key Types

| Type | Size | Values |
|------|------|--------|
| `GraphemeBreakNoControl` | u5 | 17 (adds
`indic_conjunct_break_{consonant,linker,extend}`, `emoji_modifier_base`,
`zwnj`, etc.) |
| `BreakState` | u3 | 5 (`default`, `regional_indicator`,
`extended_pictographic`, `indic_conjunct_break_consonant`,
`indic_conjunct_break_linker`) |

### Binary Size

The tables store only the `GraphemeBreakNoControl` enum per codepoint
(not width or emoji properties, which visible.zig handles separately):

- stage1: 8192 × u16 = **16KB** (maps high byte → stage2 offset)
- stage2: 27392 × u8 = **27KB** (maps to stage3 index; max value is 16)
- stage3: 17 × u5 = **~17 bytes** (one per enum value)
- Precomputed decisions: **8KB**
- **Total: ~51KB** (vs previous ~70KB+)

## How to Regenerate Tables

```bash
# After updating src/deps/uucode/:
./scripts/update-uucode.sh

# Or manually:
vendor/zig/zig build generate-grapheme-tables
```

Normal builds never run the generator — they use the committed
`grapheme_tables.zig`.

## Testing

```bash
bun bd test test/js/bun/util/stringWidth.test.ts
```

New test cases verify Devanagari conjuncts (GB9c):
- `क्ष` (Ka+Virama+Ssa) → single cluster, width 2
- `क्‍ष` (Ka+Virama+ZWJ+Ssa) → single cluster, width 2
- `क्क्क` (Ka+Virama+Ka+Virama+Ka) → single cluster, width 3

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
2026-01-23 00:07:06 -08:00

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This file contains ambiguous Unicode characters
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Bun itself is MIT-licensed.
## JavaScriptCore
Bun statically links JavaScriptCore (and WebKit) which is LGPL-2 licensed. WebCore files from WebKit are also licensed under LGPL2. Per LGPL2:
> (1) If you statically link against an LGPL’d library, you must also provide your application in an object (not necessarily source) format, so that a user has the opportunity to modify the library and relink the application.
You can find the patched version of WebKit used by Bun here: <https://github.com/oven-sh/webkit>. If you would like to relink Bun with changes:
- `git submodule update --init --recursive`
- `make jsc`
- `zig build`
This compiles JavaScriptCore, compiles Bun’s `.cpp` bindings for JavaScriptCore (which are the object files using JavaScriptCore) and outputs a new `bun` binary with your changes.
## Linked libraries
Bun statically links these libraries:
| Library | License |
|---------|---------|
| [`boringssl`](https://boringssl.googlesource.com/boringssl/) | [several licenses](https://boringssl.googlesource.com/boringssl/+/refs/heads/master/LICENSE) |
| [`brotli`](https://github.com/google/brotli) | MIT |
| [`libarchive`](https://github.com/libarchive/libarchive) | [several licenses](https://github.com/libarchive/libarchive/blob/master/COPYING) |
| [`lol-html`](https://github.com/cloudflare/lol-html/tree/master/c-api) | BSD 3-Clause |
| [`mimalloc`](https://github.com/microsoft/mimalloc) | MIT |
| [`picohttp`](https://github.com/h2o/picohttpparser) | dual-licensed under the Perl License or the MIT License |
| [`zstd`](https://github.com/facebook/zstd) | dual-licensed under the BSD License or GPLv2 license |
| [`simdutf`](https://github.com/simdutf/simdutf) | Apache 2.0 |
| [`tinycc`](https://github.com/tinycc/tinycc) | LGPL v2.1 |
| [`uSockets`](https://github.com/uNetworking/uSockets) | Apache 2.0 |
| [`zlib-cloudflare`](https://github.com/cloudflare/zlib) | zlib |
| [`c-ares`](https://github.com/c-ares/c-ares) | MIT licensed |
| [`libicu`](https://github.com/unicode-org/icu) 72 | [license here](https://github.com/unicode-org/icu/blob/main/icu4c/LICENSE) |
| [`libbase64`](https://github.com/aklomp/base64/blob/master/LICENSE) | BSD 2-Clause |
| [`libuv`](https://github.com/libuv/libuv) (on Windows) | MIT |
| [`libdeflate`](https://github.com/ebiggers/libdeflate) | MIT |
| [`uucode`](https://github.com/jacobsandlund/uucode) | MIT |
| A fork of [`uWebsockets`](https://github.com/jarred-sumner/uwebsockets) | Apache 2.0 licensed |
| Parts of [Tigerbeetle's IO code](https://github.com/tigerbeetle/tigerbeetle/blob/532c8b70b9142c17e07737ab6d3da68d7500cbca/src/io/windows.zig#L1) | Apache 2.0 licensed |
## Polyfills
For compatibility reasons, the following packages are embedded into Bun's binary and injected if imported.
| Package | License |
|---------|---------|
| [`assert`](https://npmjs.com/package/assert) | MIT |
| [`browserify-zlib`](https://npmjs.com/package/browserify-zlib) | MIT |
| [`buffer`](https://npmjs.com/package/buffer) | MIT |
| [`constants-browserify`](https://npmjs.com/package/constants-browserify) | MIT |
| [`crypto-browserify`](https://npmjs.com/package/crypto-browserify) | MIT |
| [`domain-browser`](https://npmjs.com/package/domain-browser) | MIT |
| [`events`](https://npmjs.com/package/events) | MIT |
| [`https-browserify`](https://npmjs.com/package/https-browserify) | MIT |
| [`os-browserify`](https://npmjs.com/package/os-browserify) | MIT |
| [`path-browserify`](https://npmjs.com/package/path-browserify) | MIT |
| [`process`](https://npmjs.com/package/process) | MIT |
| [`punycode`](https://npmjs.com/package/punycode) | MIT |
| [`querystring-es3`](https://npmjs.com/package/querystring-es3) | MIT |
| [`stream-browserify`](https://npmjs.com/package/stream-browserify) | MIT |
| [`stream-http`](https://npmjs.com/package/stream-http) | MIT |
| [`string_decoder`](https://npmjs.com/package/string_decoder) | MIT |
| [`timers-browserify`](https://npmjs.com/package/timers-browserify) | MIT |
| [`tty-browserify`](https://npmjs.com/package/tty-browserify) | MIT |
| [`url`](https://npmjs.com/package/url) | MIT |
| [`util`](https://npmjs.com/package/util) | MIT |
| [`vm-browserify`](https://npmjs.com/package/vm-browserify) | MIT |
## Additional credits
- Bun's JS transpiler, CSS lexer, and Node.js module resolver source code is a Zig port of [@evanw](https://github.com/evanw)’s [esbuild](https://github.com/evanw/esbuild) project.
- Credit to [@kipply](https://github.com/kipply) for the name "Bun"!
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