[dylan-conway]

Summary

Removes the deprecated ZigString type from the public API, migrating all callers to bun.String/BunString. The internal 16-byte {ptr, len} tagged-pointer struct remains as the backing storage for borrowed string views, but is renamed to StringView (Zig) / ZigStringView (C++) and made private.

Net: −1,028 lines across 143 files (3 commits on top of 2222aa9f47)

What changed

Deleted

Item	Size
src/bun.js/bindings/ZigString.zig	745 lines
13 ZigString__* C++ FFI functions (bindings.cpp)	~150 lines
bun.ZigString / jsc.ZigString public exports	—
ErrorableZigString type (unused)	—
Dead functions: getCachedObject, putCachedObject, JSObject.getDirect/putDirect, JSValue.createTypeError/createRangeError, JSValue.putRecord	—
jsc.ZigString case from wrapInstanceMethod/wrapStaticMethod	—
~140 lines of dead Zig:: helper functions (helpers.h)	—

Renamed

Old	New	Where
ZigString struct	StringView	Zig (string.zig, private)
ZigString struct	ZigStringView	C++ (headers-handwritten.h)
Tag.ZigString / .StaticZigString	Tag.StringView / .StaticStringView	Both
BunStringImpl.zig	BunStringImpl.view	C++ union field
String.toZigString() (public)	asStringViewUnsafe() (private)	Zig — safety fix: borrows WTFStringImpl bytes
ZigString__freeGlobal	BunString__freeGlobalBytes	FFI export
trait.isZigString()	trait.isStringSlice()	Unrelated naming collision

Converted (~30 FFI functions, ~1000+ call sites)

Zig call-site patterns:

Old	New
obj.put(g, ZigString.static("key"), val)	obj.put(g, bun.String.static("key"), val) (~350 sites)
ZigString.init(s).withEncoding().toJS(g)	try bun.String.createUTF8ForJS(g, s) (~100 sites)
ZigString.init(msg).toErrorInstance(g)	bun.String.borrowUTF8(msg).toErrorInstance(g) (~50 sites)
ZigString.Slice	bun.String.Slice (~200 sites)
ZigString.init("").toJS(g)	jsEmptyString(g)

FFI extern signatures (ZigString* → BunString*):

• Output params (ref-counted via Bun::toStringRef): getClassName, getNameProperty, getSymbolDescription, symbolKeyFor, getSourceCode, DOMURL.pathname_
• Output params (borrowed via Bun::toString/toStringView): JSValue.toBunString, JSString.toBunString, FetchHeaders.fastGet_/get_, DOMURL.href_
• Input params (copied via toWTFString()): createObject2, symbolFor, createAggregateError, deleteModuleRegistryEntry, setTimeZone, deleteProperty, put, FetchHeaders.*, DOMFormData.*, URLSearchParams.*
• Callbacks: forEachProperty (3 variants), DOMFormData.forEach/toQueryString, URLSearchParams.toString
• Arrays: putRecord, fromEntries, ServerRouteList.create
• WebSocket: 14-param connect + writeString + close + didReceiveText
• Others: Bun__Buffer_fill, Bun__Process__setCwd, Bun__getEnvValue, resolve queryString, CodeString

wrapInstanceMethod params (html_rewriter 27 methods, CryptoHasher, EVP, server.publish, FFI.open): ZigString → bun.String, uses borrowed toString() (no ref overhead, matching old behavior).

Memory & performance audit

Pattern	Before	After	Verdict
INPUT (Zig→C++, .ZigString tag)	Zig::toString() borrows latin1, copies UTF8	toWTFString() always copies	Safer (no borrow lifetime dep)
OUTPUT w/ toStringRef	toZigString() borrows raw ptr	Bun::toStringRef() +1 ref, Zig derefs	Safer (explicit ownership)
OUTPUT w/ toString (no ref)	Borrows impl via COW share	Same — relies on source holding ref	Identical
OUTPUT w/ toStringView	Borrows raw bytes	Same — .StringView tag	Identical
.put() static keys	toIdentifier → copy → atomize	toWTFString() → copy → atomize	Identical
FetchHeaders get/has/remove	Zig::toString() borrow	toWTFString(ZeroCopy) borrow	Identical (fixed after initial conversion added unnecessary copy)
wrapInstanceMethod params	getZigString() borrow (0 ref overhead)	toString() borrow (0 ref overhead)	Identical
.static().toJS()	toStringCopy copies	toStringStatic → ASCIILiteral zero-copy	Faster

Testing

• bun run zig:check-all — 61/61 platforms pass
• bun bd — compiles
• Smoke tests: fetch (341), inspect (71), serve (189), node:os (52), node:path (116), html-rewriter (41), websocket, FormData, DNS, crypto, ffi, spawn — 0 regressions

Pre-existing failures (unchanged from main): websocket-client.test.ts (needs ws npm pkg), resolve.test.ts (needs tsyringe), expect.test.js stress test timeout.

Architecture

Before:

bun.ZigString / jsc.ZigString  ←── public 16-byte tagged {ptr, len}
       │
       └── used directly by ~1400 call sites + 30+ extern C functions

After:

bun.String  ←── only public string type
    │
    └── private StringView (16-byte {ptr, len})  ←── .StringView / .StaticStringView variants
               ↕ (ABI only)
    ZigStringView  ←── C++ internal struct, only inside BunStringImpl union

The .StringView/.StaticStringView variants mean "Zig-owned bytes, C++ must copy". The .WTFStringImpl variant means "JSC-owned, ref-counted".

[robobun]

^{Updated 4:15 AM PT - Feb 27th, 2026}

❌ @dylan-conway, your commit 47cb5a3 has 5 failures in Build #38260 (All Failures):

• test/js/node/http/node-http-backpressure-max.test.ts - 1 failing on 🍎 13 x64
• test/regression/issue/8254.test.ts - 1 failing on 🍎 13 aarch64
• test/integration/next-pages/test/dev-server.test.ts - 1 failing on 🍎 14 aarch64
• test/regression/issue/11297/11297.test.ts - 1 failing on 🪟 11 aarch64
• test/regression/issue/11297/11297.test.ts - 1 failing on 🪟 2019 x64-baseline
• test/integration/vite-build/vite-build.test.ts - 1 failing on 🪟 2019 x64-baseline

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🧪   To try this PR locally:

bunx bun-pr 27473

That installs a local version of the PR into your bun-27473 executable, so you can run:

bun-27473 --bun