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chore: convert .cursor/rules to .claude/skills (#25683)

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## Summary
- Migrate Cursor rules to Claude Code skills format
- Add 4 new skills for development guidance:
  - `writing-dev-server-tests`: HMR/dev server test guidance
  - `implementing-jsc-classes-cpp`: C++ JSC class implementation  
  - `implementing-jsc-classes-zig`: Zig JSC bindings generator
  - `writing-bundler-tests`: bundler test guidance with itBundled
- Remove all `.cursor/rules/` files

## Test plan
- [x] Skills follow Claude Code skill authoring guidelines
- [x] Each skill has proper YAML frontmatter with name and description
- [x] Skills are concise and actionable

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

---------

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
robobun
2025-12-24 23:37:26 -08:00
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commit 2247c3859a
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---
name: implementing-jsc-classes-cpp
description: Implements JavaScript classes in C++ using JavaScriptCore. Use when creating new JS classes with C++ bindings, prototypes, or constructors.
---
# Implementing JavaScript Classes in C++
## Class Structure
For publicly accessible Constructor and Prototype, create 3 classes:
1. **`class Foo : public JSC::DestructibleObject`** - if C++ fields exist; otherwise use `JSC::constructEmptyObject` with `putDirectOffset`
2. **`class FooPrototype : public JSC::JSNonFinalObject`**
3. **`class FooConstructor : public JSC::InternalFunction`**
No public constructor? Only Prototype and class needed.
## Iso Subspaces
Classes with C++ fields need subspaces in:
- `src/bun.js/bindings/webcore/DOMClientIsoSubspaces.h`
- `src/bun.js/bindings/webcore/DOMIsoSubspaces.h`
```cpp
template<typename MyClassT, JSC::SubspaceAccess mode>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) {
if constexpr (mode == JSC::SubspaceAccess::Concurrently)
return nullptr;
return WebCore::subspaceForImpl<MyClassT, WebCore::UseCustomHeapCellType::No>(
vm,
[](auto& spaces) { return spaces.m_clientSubspaceForMyClassT.get(); },
[](auto& spaces, auto&& space) { spaces.m_clientSubspaceForMyClassT = std::forward<decltype(space)>(space); },
[](auto& spaces) { return spaces.m_subspaceForMyClassT.get(); },
[](auto& spaces, auto&& space) { spaces.m_subspaceForMyClassT = std::forward<decltype(space)>(space); });
}
```
## Property Definitions
```cpp
static JSC_DECLARE_HOST_FUNCTION(jsFooProtoFuncMethod);
static JSC_DECLARE_CUSTOM_GETTER(jsFooGetter_property);
static const HashTableValue JSFooPrototypeTableValues[] = {
{ "property"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsFooGetter_property, 0 } },
{ "method"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsFooProtoFuncMethod, 1 } },
};
```
## Prototype Class
```cpp
class JSFooPrototype final : public JSC::JSNonFinalObject {
public:
using Base = JSC::JSNonFinalObject;
static constexpr unsigned StructureFlags = Base::StructureFlags;
static JSFooPrototype* create(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::Structure* structure) {
JSFooPrototype* prototype = new (NotNull, allocateCell<JSFooPrototype>(vm)) JSFooPrototype(vm, structure);
prototype->finishCreation(vm);
return prototype;
}
template<typename, JSC::SubspaceAccess>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) { return &vm.plainObjectSpace(); }
DECLARE_INFO;
static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype) {
auto* structure = JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::ObjectType, StructureFlags), info());
structure->setMayBePrototype(true);
return structure;
}
private:
JSFooPrototype(JSC::VM& vm, JSC::Structure* structure) : Base(vm, structure) {}
void finishCreation(JSC::VM& vm);
};
void JSFooPrototype::finishCreation(VM& vm) {
Base::finishCreation(vm);
reifyStaticProperties(vm, JSFoo::info(), JSFooPrototypeTableValues, *this);
JSC_TO_STRING_TAG_WITHOUT_TRANSITION();
}
```
## Getter/Setter/Function Definitions
```cpp
// Getter
JSC_DEFINE_CUSTOM_GETTER(jsFooGetter_prop, (JSGlobalObject* globalObject, EncodedJSValue thisValue, PropertyName)) {
VM& vm = globalObject->vm();
auto scope = DECLARE_THROW_SCOPE(vm);
JSFoo* thisObject = jsDynamicCast<JSFoo*>(JSValue::decode(thisValue));
if (UNLIKELY(!thisObject)) {
Bun::throwThisTypeError(*globalObject, scope, "JSFoo"_s, "prop"_s);
return {};
}
return JSValue::encode(jsBoolean(thisObject->value()));
}
// Function
JSC_DEFINE_HOST_FUNCTION(jsFooProtoFuncMethod, (JSGlobalObject* globalObject, CallFrame* callFrame)) {
VM& vm = globalObject->vm();
auto scope = DECLARE_THROW_SCOPE(vm);
auto* thisObject = jsDynamicCast<JSFoo*>(callFrame->thisValue());
if (UNLIKELY(!thisObject)) {
Bun::throwThisTypeError(*globalObject, scope, "Foo"_s, "method"_s);
return {};
}
return JSValue::encode(thisObject->doSomething(vm, globalObject));
}
```
## Constructor Class
```cpp
class JSFooConstructor final : public JSC::InternalFunction {
public:
using Base = JSC::InternalFunction;
static constexpr unsigned StructureFlags = Base::StructureFlags;
static JSFooConstructor* create(JSC::VM& vm, JSC::Structure* structure, JSC::JSObject* prototype) {
JSFooConstructor* constructor = new (NotNull, JSC::allocateCell<JSFooConstructor>(vm)) JSFooConstructor(vm, structure);
constructor->finishCreation(vm, prototype);
return constructor;
}
DECLARE_INFO;
template<typename CellType, JSC::SubspaceAccess>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) { return &vm.internalFunctionSpace(); }
static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype) {
return JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::InternalFunctionType, StructureFlags), info());
}
private:
JSFooConstructor(JSC::VM& vm, JSC::Structure* structure) : Base(vm, structure, callFoo, constructFoo) {}
void finishCreation(JSC::VM& vm, JSC::JSObject* prototype) {
Base::finishCreation(vm, 0, "Foo"_s);
putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, JSC::PropertyAttribute::DontEnum | JSC::PropertyAttribute::DontDelete | JSC::PropertyAttribute::ReadOnly);
}
};
```
## Structure Caching
Add to `ZigGlobalObject.h`:
```cpp
JSC::LazyClassStructure m_JSFooClassStructure;
```
Initialize in `ZigGlobalObject.cpp`:
```cpp
m_JSFooClassStructure.initLater([](LazyClassStructure::Initializer& init) {
Bun::initJSFooClassStructure(init);
});
```
Visit in `visitChildrenImpl`:
```cpp
m_JSFooClassStructure.visit(visitor);
```
## Expose to Zig
```cpp
extern "C" JSC::EncodedJSValue Bun__JSFooConstructor(Zig::GlobalObject* globalObject) {
return JSValue::encode(globalObject->m_JSFooClassStructure.constructor(globalObject));
}
extern "C" EncodedJSValue Bun__Foo__toJS(Zig::GlobalObject* globalObject, Foo* foo) {
auto* structure = globalObject->m_JSFooClassStructure.get(globalObject);
return JSValue::encode(JSFoo::create(globalObject->vm(), structure, globalObject, WTFMove(foo)));
}
```
Include `#include "root.h"` at the top of C++ files.

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---
name: implementing-jsc-classes-zig
description: Creates JavaScript classes using Bun's Zig bindings generator (.classes.ts). Use when implementing new JS APIs in Zig with JSC integration.
---
# Bun's JavaScriptCore Class Bindings Generator
Bridge JavaScript and Zig through `.classes.ts` definitions and Zig implementations.
## Architecture
1. **Zig Implementation** (.zig files)
2. **JavaScript Interface Definition** (.classes.ts files)
3. **Generated Code** (C++/Zig files connecting them)
## Class Definition (.classes.ts)
```typescript
define({
name: "TextDecoder",
constructor: true,
JSType: "object",
finalize: true,
proto: {
decode: { args: 1 },
encoding: { getter: true, cache: true },
fatal: { getter: true },
},
});
```
Options:
- `name`: Class name
- `constructor`: Has public constructor
- `JSType`: "object", "function", etc.
- `finalize`: Needs cleanup
- `proto`: Properties/methods
- `cache`: Cache property values via WriteBarrier
## Zig Implementation
```zig
pub const TextDecoder = struct {
pub const js = JSC.Codegen.JSTextDecoder;
pub const toJS = js.toJS;
pub const fromJS = js.fromJS;
pub const fromJSDirect = js.fromJSDirect;
encoding: []const u8,
fatal: bool,
pub fn constructor(
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!*TextDecoder {
return bun.new(TextDecoder, .{ .encoding = "utf-8", .fatal = false });
}
pub fn decode(
this: *TextDecoder,
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!JSC.JSValue {
const args = callFrame.arguments();
if (args.len < 1 or args.ptr[0].isUndefinedOrNull()) {
return globalObject.throw("Input cannot be null", .{});
}
return JSC.JSValue.jsString(globalObject, "result");
}
pub fn getEncoding(this: *TextDecoder, globalObject: *JSGlobalObject) JSC.JSValue {
return JSC.JSValue.createStringFromUTF8(globalObject, this.encoding);
}
fn deinit(this: *TextDecoder) void {
// Release resources
}
pub fn finalize(this: *TextDecoder) void {
this.deinit();
bun.destroy(this);
}
};
```
**Key patterns:**
- Use `bun.JSError!JSValue` return type for error handling
- Use `globalObject` not `ctx`
- `deinit()` for cleanup, `finalize()` called by GC
- Update `src/bun.js/bindings/generated_classes_list.zig`
## CallFrame Access
```zig
const args = callFrame.arguments();
const first_arg = args.ptr[0]; // Access as slice
const argCount = args.len;
const thisValue = callFrame.thisValue();
```
## Property Caching
For `cache: true` properties, generated accessors:
```zig
// Get cached value
pub fn encodingGetCached(thisValue: JSC.JSValue) ?JSC.JSValue {
const result = TextDecoderPrototype__encodingGetCachedValue(thisValue);
if (result == .zero) return null;
return result;
}
// Set cached value
pub fn encodingSetCached(thisValue: JSC.JSValue, globalObject: *JSC.JSGlobalObject, value: JSC.JSValue) void {
TextDecoderPrototype__encodingSetCachedValue(thisValue, globalObject, value);
}
```
## Error Handling
```zig
pub fn method(this: *MyClass, globalObject: *JSGlobalObject, callFrame: *JSC.CallFrame) bun.JSError!JSC.JSValue {
const args = callFrame.arguments();
if (args.len < 1) {
return globalObject.throw("Missing required argument", .{});
}
return JSC.JSValue.jsString(globalObject, "Success!");
}
```
## Memory Management
```zig
pub fn deinit(this: *TextDecoder) void {
this._encoding.deref();
if (this.buffer) |buffer| {
bun.default_allocator.free(buffer);
}
}
pub fn finalize(this: *TextDecoder) void {
JSC.markBinding(@src());
this.deinit();
bun.default_allocator.destroy(this);
}
```
## Creating a New Binding
1. Define interface in `.classes.ts`:
```typescript
define({
name: "MyClass",
constructor: true,
finalize: true,
proto: {
myMethod: { args: 1 },
myProperty: { getter: true, cache: true },
},
});
```
2. Implement in `.zig`:
```zig
pub const MyClass = struct {
pub const js = JSC.Codegen.JSMyClass;
pub const toJS = js.toJS;
pub const fromJS = js.fromJS;
value: []const u8,
pub const new = bun.TrivialNew(@This());
pub fn constructor(globalObject: *JSGlobalObject, callFrame: *JSC.CallFrame) bun.JSError!*MyClass {
return MyClass.new(.{ .value = "" });
}
pub fn myMethod(this: *MyClass, globalObject: *JSGlobalObject, callFrame: *JSC.CallFrame) bun.JSError!JSC.JSValue {
return JSC.JSValue.jsUndefined();
}
pub fn getMyProperty(this: *MyClass, globalObject: *JSGlobalObject) JSC.JSValue {
return JSC.JSValue.jsString(globalObject, this.value);
}
pub fn deinit(this: *MyClass) void {}
pub fn finalize(this: *MyClass) void {
this.deinit();
bun.destroy(this);
}
};
```
3. Add to `src/bun.js/bindings/generated_classes_list.zig`
## Generated Components
- **C++ Classes**: `JSMyClass`, `JSMyClassPrototype`, `JSMyClassConstructor`
- **Method Bindings**: `MyClassPrototype__myMethodCallback`
- **Property Accessors**: `MyClassPrototype__myPropertyGetterWrap`
- **Zig Bindings**: External function declarations, cached value accessors

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---
name: writing-bundler-tests
description: Guides writing bundler tests using itBundled/expectBundled in test/bundler/. Use when creating or modifying bundler, transpiler, or code transformation tests.
---
# Writing Bundler Tests
Bundler tests use `itBundled()` from `test/bundler/expectBundled.ts` to test Bun's bundler.
## Basic Usage
```typescript
import { describe } from "bun:test";
import { itBundled, dedent } from "./expectBundled";
describe("bundler", () => {
itBundled("category/TestName", {
files: {
"index.js": `console.log("hello");`,
},
run: {
stdout: "hello",
},
});
});
```
Test ID format: `category/TestName` (e.g., `banner/CommentBanner`, `minify/Empty`)
## File Setup
```typescript
{
files: {
"index.js": `console.log("test");`,
"lib.ts": `export const foo = 123;`,
"nested/file.js": `export default {};`,
},
entryPoints: ["index.js"], // defaults to first file
runtimeFiles: { // written AFTER bundling
"extra.js": `console.log("added later");`,
},
}
```
## Bundler Options
```typescript
{
outfile: "/out.js",
outdir: "/out",
format: "esm" | "cjs" | "iife",
target: "bun" | "browser" | "node",
// Minification
minifyWhitespace: true,
minifyIdentifiers: true,
minifySyntax: true,
// Code manipulation
banner: "// copyright",
footer: "// end",
define: { "PROD": "true" },
external: ["lodash"],
// Advanced
sourceMap: "inline" | "external",
splitting: true,
treeShaking: true,
drop: ["console"],
}
```
## Runtime Verification
```typescript
{
run: {
stdout: "expected output", // exact match
stdout: /regex/, // pattern match
partialStdout: "contains this", // substring
stderr: "error output",
exitCode: 1,
env: { NODE_ENV: "production" },
runtime: "bun" | "node",
// Runtime errors
error: "ReferenceError: x is not defined",
},
}
```
## Bundle Errors/Warnings
```typescript
{
bundleErrors: {
"/file.js": ["error message 1", "error message 2"],
},
bundleWarnings: {
"/file.js": ["warning message"],
},
}
```
## Dead Code Elimination (DCE)
Add markers in source code:
```javascript
// KEEP - this should survive
const used = 1;
// REMOVE - this should be eliminated
const unused = 2;
```
```typescript
{
dce: true,
dceKeepMarkerCount: 5, // expected KEEP markers
}
```
## Capture Pattern
Verify exact transpilation with `capture()`:
```typescript
itBundled("string/Folding", {
files: {
"index.ts": `capture(\`\${1 + 1}\`);`,
},
capture: ['"2"'], // expected captured value
minifySyntax: true,
});
```
## Post-Bundle Assertions
```typescript
{
onAfterBundle(api) {
api.expectFile("out.js").toContain("console.log");
api.assertFileExists("out.js");
const content = api.readFile("out.js");
expect(content).toMatchSnapshot();
const values = api.captureFile("out.js");
expect(values).toEqual(["2"]);
},
}
```
## Common Patterns
**Simple output verification:**
```typescript
itBundled("banner/Comment", {
banner: "// copyright",
files: { "a.js": `console.log("Hello")` },
onAfterBundle(api) {
api.expectFile("out.js").toContain("// copyright");
},
});
```
**Multi-file CJS/ESM interop:**
```typescript
itBundled("cjs/ImportSyntax", {
files: {
"entry.js": `import lib from './lib.cjs'; console.log(lib);`,
"lib.cjs": `exports.foo = 'bar';`,
},
run: { stdout: '{"foo":"bar"}' },
});
```
**Error handling:**
```typescript
itBundled("edgecase/InvalidLoader", {
files: { "index.js": `...` },
bundleErrors: {
"index.js": ["Unsupported loader type"],
},
});
```
## Test Organization
```text
test/bundler/
├── bundler_banner.test.ts
├── bundler_string.test.ts
├── bundler_minify.test.ts
├── bundler_cjs.test.ts
├── bundler_edgecase.test.ts
├── bundler_splitting.test.ts
├── css/
├── transpiler/
└── expectBundled.ts
```
## Running Tests
```bash
bun bd test test/bundler/bundler_banner.test.ts
BUN_BUNDLER_TEST_FILTER="banner/Comment" bun bd test bundler_banner.test.ts
BUN_BUNDLER_TEST_DEBUG=1 bun bd test bundler_minify.test.ts
```
## Key Points
- Use `dedent` for readable multi-line code
- File paths are relative (e.g., `/index.js`)
- Use `capture()` to verify exact transpilation results
- Use `.toMatchSnapshot()` for complex outputs
- Pass array to `run` for multiple test scenarios

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---
name: writing-dev-server-tests
description: Guides writing HMR/Dev Server tests in test/bake/. Use when creating or modifying dev server, hot reloading, or bundling tests.
---
# Writing HMR/Dev Server Tests
Dev server tests validate hot-reloading robustness and reliability.
## File Structure
- `test/bake/bake-harness.ts` - shared utilities: `devTest`, `prodTest`, `devAndProductionTest`, `Dev` class, `Client` class
- `test/bake/client-fixture.mjs` - subprocess for `Client` (page loading, IPC queries)
- `test/bake/dev/*.test.ts` - dev server and hot reload tests
- `test/bake/dev-and-prod.ts` - tests running on both dev and production mode
## Test Categories
- `bundle.test.ts` - DevServer-specific bundling bugs
- `css.test.ts` - CSS bundling issues
- `plugins.test.ts` - development mode plugins
- `ecosystem.test.ts` - library compatibility (prefer concrete bugs over full package tests)
- `esm.test.ts` - ESM features in development
- `html.test.ts` - HTML file handling
- `react-spa.test.ts` - React, react-refresh transform, server components
- `sourcemap.test.ts` - source map correctness
## devTest Basics
```ts
import { devTest, emptyHtmlFile } from "../bake-harness";
devTest("html file is watched", {
files: {
"index.html": emptyHtmlFile({
scripts: ["/script.ts"],
body: "<h1>Hello</h1>",
}),
"script.ts": `console.log("hello");`,
},
async test(dev) {
await dev.fetch("/").expect.toInclude("<h1>Hello</h1>");
await dev.patch("index.html", { find: "Hello", replace: "World" });
await dev.fetch("/").expect.toInclude("<h1>World</h1>");
await using c = await dev.client("/");
await c.expectMessage("hello");
await c.expectReload(async () => {
await dev.patch("index.html", { find: "World", replace: "Bar" });
});
await c.expectMessage("hello");
},
});
```
## Key APIs
- **`files`**: Initial filesystem state
- **`dev.fetch()`**: HTTP requests
- **`dev.client()`**: Opens browser instance
- **`dev.write/patch/delete`**: Filesystem mutations (wait for hot-reload automatically)
- **`c.expectMessage()`**: Assert console.log output
- **`c.expectReload()`**: Wrap code that causes hard reload
**Important**: Use `dev.write/patch/delete` instead of `node:fs` - they wait for hot-reload.
## Testing Errors
```ts
devTest("import then create", {
files: {
"index.html": `<!DOCTYPE html><html><head></head><body><script type="module" src="/script.ts"></script></body></html>`,
"script.ts": `import data from "./data"; console.log(data);`,
},
async test(dev) {
const c = await dev.client("/", {
errors: ['script.ts:1:18: error: Could not resolve: "./data"'],
});
await c.expectReload(async () => {
await dev.write("data.ts", "export default 'data';");
});
await c.expectMessage("data");
},
});
```
Specify expected errors with the `errors` option:
```ts
await dev.delete("other.ts", {
errors: ['index.ts:1:16: error: Could not resolve: "./other"'],
});
```

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---
name: zig-system-calls
description: Guides using bun.sys for system calls and file I/O in Zig. Use when implementing file operations instead of std.fs or std.posix.
---
# System Calls & File I/O in Zig
Use `bun.sys` instead of `std.fs` or `std.posix` for cross-platform syscalls with proper error handling.
## bun.sys.File (Preferred)
For most file operations, use the `bun.sys.File` wrapper:
```zig
const File = bun.sys.File;
const file = switch (File.open(path, bun.O.RDWR, 0o644)) {
.result => |f| f,
.err => |err| return .{ .err = err },
};
defer file.close();
// Read/write
_ = try file.read(buffer).unwrap();
_ = try file.writeAll(data).unwrap();
// Get file info
const stat = try file.stat().unwrap();
const size = try file.getEndPos().unwrap();
// std.io compatible
const reader = file.reader();
const writer = file.writer();
```
### Complete Example
```zig
const File = bun.sys.File;
pub fn writeFile(path: [:0]const u8, data: []const u8) File.WriteError!void {
const file = switch (File.open(path, bun.O.WRONLY | bun.O.CREAT | bun.O.TRUNC, 0o664)) {
.result => |f| f,
.err => |err| return err.toError(),
};
defer file.close();
_ = switch (file.writeAll(data)) {
.result => {},
.err => |err| return err.toError(),
};
}
```
## Why bun.sys?
| Aspect | bun.sys | std.fs/std.posix |
| ----------- | -------------------------------- | ------------------- |
| Return Type | `Maybe(T)` with detailed Error | Generic error union |
| Windows | Full support with libuv fallback | Limited/POSIX-only |
| Error Info | errno, syscall tag, path, fd | errno only |
| EINTR | Automatic retry | Manual handling |
## Error Handling with Maybe(T)
`bun.sys` functions return `Maybe(T)` - a tagged union:
```zig
const sys = bun.sys;
// Pattern 1: Switch on result/error
switch (sys.read(fd, buffer)) {
.result => |bytes_read| {
// use bytes_read
},
.err => |err| {
// err.errno, err.syscall, err.fd, err.path
if (err.getErrno() == .AGAIN) {
// handle EAGAIN
}
},
}
// Pattern 2: Unwrap with try (converts to Zig error)
const bytes = try sys.read(fd, buffer).unwrap();
// Pattern 3: Unwrap with default
const value = sys.stat(path).unwrapOr(default_stat);
```
## Low-Level File Operations
Only use these when `bun.sys.File` doesn't meet your needs.
### Opening Files
```zig
const sys = bun.sys;
// Use bun.O flags (cross-platform normalized)
const fd = switch (sys.open(path, bun.O.RDONLY, 0)) {
.result => |fd| fd,
.err => |err| return .{ .err = err },
};
defer fd.close();
// Common flags
bun.O.RDONLY, bun.O.WRONLY, bun.O.RDWR
bun.O.CREAT, bun.O.TRUNC, bun.O.APPEND
bun.O.NONBLOCK, bun.O.DIRECTORY
```
### Reading & Writing
```zig
// Single read (may return less than buffer size)
switch (sys.read(fd, buffer)) {
.result => |n| { /* n bytes read */ },
.err => |err| { /* handle error */ },
}
// Read until EOF or buffer full
const total = try sys.readAll(fd, buffer).unwrap();
// Position-based read/write
sys.pread(fd, buffer, offset)
sys.pwrite(fd, data, offset)
// Vector I/O
sys.readv(fd, iovecs)
sys.writev(fd, iovecs)
```
### File Info
```zig
sys.stat(path) // Follow symlinks
sys.lstat(path) // Don't follow symlinks
sys.fstat(fd) // From file descriptor
sys.fstatat(fd, path)
// Linux-only: faster selective stat
sys.statx(path, &.{ .size, .mtime })
```
### Path Operations
```zig
sys.unlink(path)
sys.unlinkat(dir_fd, path)
sys.rename(from, to)
sys.renameat(from_dir, from, to_dir, to)
sys.readlink(path, buf)
sys.readlinkat(fd, path, buf)
sys.link(T, src, dest)
sys.linkat(src_fd, src, dest_fd, dest)
sys.symlink(target, dest)
sys.symlinkat(target, dirfd, dest)
sys.mkdir(path, mode)
sys.mkdirat(dir_fd, path, mode)
sys.rmdir(path)
```
### Permissions
```zig
sys.chmod(path, mode)
sys.fchmod(fd, mode)
sys.fchmodat(fd, path, mode, flags)
sys.chown(path, uid, gid)
sys.fchown(fd, uid, gid)
```
### Closing File Descriptors
Close is on `bun.FD`:
```zig
fd.close(); // Asserts on error (use in defer)
// Or if you need error info:
if (fd.closeAllowingBadFileDescriptor(null)) |err| {
// handle error
}
```
## Directory Operations
```zig
var buf: bun.PathBuffer = undefined;
const cwd = try sys.getcwd(&buf).unwrap();
const cwdZ = try sys.getcwdZ(&buf).unwrap(); // Zero-terminated
sys.chdir(path, destination)
```
### Directory Iteration
Use `bun.DirIterator` instead of `std.fs.Dir.Iterator`:
```zig
var iter = bun.iterateDir(dir_fd);
while (true) {
switch (iter.next()) {
.result => |entry| {
if (entry) |e| {
const name = e.name.slice();
const kind = e.kind; // .file, .directory, .sym_link, etc.
} else {
break; // End of directory
}
},
.err => |err| return .{ .err = err },
}
}
```
## Socket Operations
**Important**: `bun.sys` has limited socket support. For network I/O:
- **Non-blocking sockets**: Use `uws.Socket` (libuwebsockets) exclusively
- **Pipes/blocking I/O**: Use `PipeReader.zig` and `PipeWriter.zig`
Available in bun.sys:
```zig
sys.setsockopt(fd, level, optname, value)
sys.socketpair(domain, socktype, protocol, nonblocking_status)
```
Do NOT use `bun.sys` for socket read/write - use `uws.Socket` instead.
## Other Operations
```zig
sys.ftruncate(fd, size)
sys.lseek(fd, offset, whence)
sys.dup(fd)
sys.dupWithFlags(fd, flags)
sys.fcntl(fd, cmd, arg)
sys.pipe()
sys.mmap(...)
sys.munmap(memory)
sys.access(path, mode)
sys.futimens(fd, atime, mtime)
sys.utimens(path, atime, mtime)
```
## Error Type
```zig
const err: bun.sys.Error = ...;
err.errno // Raw errno value
err.getErrno() // As std.posix.E enum
err.syscall // Which syscall failed (Tag enum)
err.fd // Optional: file descriptor
err.path // Optional: path string
```
## Key Points
- Prefer `bun.sys.File` wrapper for most file operations
- Use low-level `bun.sys` functions only when needed
- Use `bun.O.*` flags instead of `std.os.O.*`
- Handle `Maybe(T)` with switch or `.unwrap()`
- Use `defer fd.close()` for cleanup
- EINTR is handled automatically in most functions
- For sockets, use `uws.Socket` not `bun.sys`

41
.cursor/rules/building-bun.mdc
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@@ -1,41 +0,0 @@
---
description:
globs: src/**/*.cpp,src/**/*.zig
alwaysApply: false
---
### Build Commands
- **Build debug version**: `bun bd` or `bun run build:debug`
- Creates a debug build at `./build/debug/bun-debug`
- Compilation takes ~2.5 minutes
- **Run tests with your debug build**: `bun bd test <test-file>`
- **CRITICAL**: Never use `bun test` directly - it won't include your changes
- **Run any command with debug build**: `bun bd <command>`
### Run a file
To run a file, use:
```sh
bun bd <file> <...args>
```
**CRITICAL**: Never use `bun <file>` directly. It will not have your changes.
### Logging
`BUN_DEBUG_$(SCOPE)=1` enables debug logs for a specific debug log scope.
Debug logs look like this:
```zig
const log = bun.Output.scoped(.${SCOPE}, .hidden);
// ...later
log("MY DEBUG LOG", .{})
```
### Code Generation
Code generation happens automatically as part of the build process. There are no commands to run.

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@@ -1,139 +0,0 @@
---
description: Writing HMR/Dev Server tests
globs: test/bake/*
---
# Writing HMR/Dev Server tests
Dev server tests validate that hot-reloading is robust, correct, and reliable. Remember to write thorough, yet concise tests.
## File Structure
- `test/bake/bake-harness.ts` - shared utilities and test harness
- primary test functions `devTest` / `prodTest` / `devAndProductionTest`
- class `Dev` (controls subprocess for dev server)
- class `Client` (controls a happy-dom subprocess for having the page open)
- more helpers
- `test/bake/client-fixture.mjs` - subprocess for what `Client` controls. it loads a page and uses IPC to query parts of the page, run javascript, and much more.
- `test/bake/dev/*.test.ts` - these call `devTest` to test dev server and hot reloading
- `test/bake/dev-and-prod.ts` - these use `devAndProductionTest` to run the same test on dev and production mode. these tests cannot really test hot reloading for obvious reasons.
## Categories
bundle.test.ts - Bundle tests are tests concerning bundling bugs that only occur in DevServer.
css.test.ts - CSS tests concern bundling bugs with CSS files
plugins.test.ts - Plugin tests concern plugins in development mode.
ecosystem.test.ts - These tests involve ensuring certain libraries are correct. It is preferred to test more concrete bugs than testing entire packages.
esm.test.ts - ESM tests are about various esm features in development mode.
html.test.ts - HTML tests are tests relating to HTML files themselves.
react-spa.test.ts - Tests relating to React, our react-refresh transform, and basic server component transforms.
sourcemap.test.ts - Tests verifying source-maps are correct.
## `devTest` Basics
A test takes in two primary inputs: `files` and `async test(dev) {`
```ts
import { devTest, emptyHtmlFile } from "../bake-harness";
devTest("html file is watched", {
files: {
"index.html": emptyHtmlFile({
scripts: ["/script.ts"],
body: "<h1>Hello</h1>",
}),
"script.ts": `
console.log("hello");
`,
},
async test(dev) {
await dev.fetch("/").expect.toInclude("<h1>Hello</h1>");
await dev.fetch("/").expect.toInclude("<h1>Hello</h1>");
await dev.patch("index.html", {
find: "Hello",
replace: "World",
});
await dev.fetch("/").expect.toInclude("<h1>World</h1>");
// Works
await using c = await dev.client("/");
await c.expectMessage("hello");
// Editing HTML reloads
await c.expectReload(async () => {
await dev.patch("index.html", {
find: "World",
replace: "Hello",
});
await dev.fetch("/").expect.toInclude("<h1>Hello</h1>");
});
await c.expectMessage("hello");
await c.expectReload(async () => {
await dev.patch("index.html", {
find: "Hello",
replace: "Bar",
});
await dev.fetch("/").expect.toInclude("<h1>Bar</h1>");
});
await c.expectMessage("hello");
await c.expectReload(async () => {
await dev.patch("script.ts", {
find: "hello",
replace: "world",
});
});
await c.expectMessage("world");
},
});
```
`files` holds the initial state, and the callback runs with the server running. `dev.fetch()` runs HTTP requests, while `dev.client()` opens a browser instance to the code.
Functions `dev.write` and `dev.patch` and `dev.delete` mutate the filesystem. Do not use `node:fs` APIs, as the dev server ones are hooked to wait for hot-reload, and all connected clients to receive changes.
When a change performs a hard-reload, that must be explicitly annotated with `expectReload`. This tells `client-fixture.mjs` that the test is meant to reload the page once; All other hard reloads automatically fail the test.
Client's have `console.log` instrumented, so that any unasserted logs fail the test. This makes it more obvious when an extra reload or re-evaluation. Messages are awaited via `c.expectMessage("log")` or with multiple arguments if there are multiple logs.
## Testing for bundling errors
By default, a client opening a page to an error will fail the test. This makes testing errors explicit.
```ts
devTest("import then create", {
files: {
"index.html": `
<!DOCTYPE html>
<html>
<head></head>
<body>
<script type="module" src="/script.ts"></script>
</body>
</html>
`,
"script.ts": `
import data from "./data";
console.log(data);
`,
},
async test(dev) {
const c = await dev.client("/", {
errors: ['script.ts:1:18: error: Could not resolve: "./data"'],
});
await c.expectReload(async () => {
await dev.write("data.ts", "export default 'data';");
});
await c.expectMessage("data");
},
});
```
Many functions take an options value to allow specifying it will produce errors. For example, this delete is going to cause a resolution failure.
```ts
await dev.delete("other.ts", {
errors: ['index.ts:1:16: error: Could not resolve: "./other"'],
});
```

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@@ -1,413 +0,0 @@
---
description: JavaScript class implemented in C++
globs: *.cpp
alwaysApply: false
---
# Implementing JavaScript classes in C++
If there is a publicly accessible Constructor and Prototype, then there are 3 classes:
- IF there are C++ class members we need a destructor, so `class Foo : public JSC::DestructibleObject`, if no C++ class fields (only JS properties) then we don't need a class at all usually. We can instead use JSC::constructEmptyObject(vm, structure) and `putDirectOffset` like in [NodeFSStatBinding.cpp](mdc:src/bun.js/bindings/NodeFSStatBinding.cpp).
- class FooPrototype : public JSC::JSNonFinalObject
- class FooConstructor : public JSC::InternalFunction
If there is no publicly accessible Constructor, just the Prototype and the class is necessary. In some cases, we can avoid the prototype entirely (but that's rare).
If there are C++ fields on the Foo class, the Foo class will need an iso subspace added to [DOMClientIsoSubspaces.h](mdc:src/bun.js/bindings/webcore/DOMClientIsoSubspaces.h) and [DOMIsoSubspaces.h](mdc:src/bun.js/bindings/webcore/DOMIsoSubspaces.h). Prototype and Constructor do not need subspaces.
Usually you'll need to #include "root.h" at the top of C++ files or you'll get lint errors.
Generally, defining the subspace looks like this:
```c++
class Foo : public JSC::DestructibleObject {
// ...
template<typename MyClassT, JSC::SubspaceAccess mode>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm)
{
if constexpr (mode == JSC::SubspaceAccess::Concurrently)
return nullptr;
return WebCore::subspaceForImpl<MyClassT, WebCore::UseCustomHeapCellType::No>(
vm,
[](auto& spaces) { return spaces.m_clientSubspaceFor${MyClassT}.get(); },
[](auto& spaces, auto&& space) { spaces.m_clientSubspaceFor${MyClassT} = std::forward<decltype(space)>(space); },
[](auto& spaces) { return spaces.m_subspaceFo${MyClassT}.get(); },
[](auto& spaces, auto&& space) { spaces.m_subspaceFor${MyClassT} = std::forward<decltype(space)>(space); });
}
```
It's better to put it in the .cpp file instead of the .h file, when possible.
## Defining properties
Define properties on the prototype. Use a const HashTableValues like this:
```C++
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncCheckEmail);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncCheckHost);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncCheckIP);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncCheckIssued);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncCheckPrivateKey);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncToJSON);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncToLegacyObject);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncToString);
static JSC_DECLARE_HOST_FUNCTION(jsX509CertificateProtoFuncVerify);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_ca);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_fingerprint);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_fingerprint256);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_fingerprint512);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_subject);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_subjectAltName);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_infoAccess);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_keyUsage);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_issuer);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_issuerCertificate);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_publicKey);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_raw);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_serialNumber);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_validFrom);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_validTo);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_validFromDate);
static JSC_DECLARE_CUSTOM_GETTER(jsX509CertificateGetter_validToDate);
static const HashTableValue JSX509CertificatePrototypeTableValues[] = {
{ "ca"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_ca, 0 } },
{ "checkEmail"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncCheckEmail, 2 } },
{ "checkHost"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncCheckHost, 2 } },
{ "checkIP"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncCheckIP, 1 } },
{ "checkIssued"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncCheckIssued, 1 } },
{ "checkPrivateKey"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncCheckPrivateKey, 1 } },
{ "fingerprint"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_fingerprint, 0 } },
{ "fingerprint256"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_fingerprint256, 0 } },
{ "fingerprint512"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_fingerprint512, 0 } },
{ "infoAccess"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_infoAccess, 0 } },
{ "issuer"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_issuer, 0 } },
{ "issuerCertificate"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_issuerCertificate, 0 } },
{ "keyUsage"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_keyUsage, 0 } },
{ "publicKey"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_publicKey, 0 } },
{ "raw"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_raw, 0 } },
{ "serialNumber"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_serialNumber, 0 } },
{ "subject"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_subject, 0 } },
{ "subjectAltName"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_subjectAltName, 0 } },
{ "toJSON"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncToJSON, 0 } },
{ "toLegacyObject"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncToLegacyObject, 0 } },
{ "toString"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncToString, 0 } },
{ "validFrom"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_validFrom, 0 } },
{ "validFromDate"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessorOrValue), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_validFromDate, 0 } },
{ "validTo"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_validTo, 0 } },
{ "validToDate"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessorOrValue), NoIntrinsic, { HashTableValue::GetterSetterType, jsX509CertificateGetter_validToDate, 0 } },
{ "verify"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsX509CertificateProtoFuncVerify, 1 } },
};
```
### Creating a prototype class
Follow a pattern like this:
```c++
class JSX509CertificatePrototype final : public JSC::JSNonFinalObject {
public:
using Base = JSC::JSNonFinalObject;
static constexpr unsigned StructureFlags = Base::StructureFlags;
static JSX509CertificatePrototype* create(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::Structure* structure)
{
JSX509CertificatePrototype* prototype = new (NotNull, allocateCell<JSX509CertificatePrototype>(vm)) JSX509CertificatePrototype(vm, structure);
prototype->finishCreation(vm);
return prototype;
}
template<typename, JSC::SubspaceAccess>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm)
{
return &vm.plainObjectSpace();
}
DECLARE_INFO;
static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype)
{
auto* structure = JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::ObjectType, StructureFlags), info());
structure->setMayBePrototype(true);
return structure;
}
private:
JSX509CertificatePrototype(JSC::VM& vm, JSC::Structure* structure)
: Base(vm, structure)
{
}
void finishCreation(JSC::VM& vm);
};
const ClassInfo JSX509CertificatePrototype::s_info = { "X509Certificate"_s, &Base::s_info, nullptr, nullptr, CREATE_METHOD_TABLE(JSX509CertificatePrototype) };
void JSX509CertificatePrototype::finishCreation(VM& vm)
{
Base::finishCreation(vm);
reifyStaticProperties(vm, JSX509Certificate::info(), JSX509CertificatePrototypeTableValues, *this);
JSC_TO_STRING_TAG_WITHOUT_TRANSITION();
}
} // namespace Bun
```
### Getter definition:
```C++
JSC_DEFINE_CUSTOM_GETTER(jsX509CertificateGetter_ca, (JSGlobalObject * globalObject, EncodedJSValue thisValue, PropertyName))
{
VM& vm = globalObject->vm();
auto scope = DECLARE_THROW_SCOPE(vm);
JSX509Certificate* thisObject = jsDynamicCast<JSX509Certificate*>(JSValue::decode(thisValue));
if (UNLIKELY(!thisObject)) {
Bun::throwThisTypeError(*globalObject, scope, "JSX509Certificate"_s, "ca"_s);
return {};
}
return JSValue::encode(jsBoolean(thisObject->view().isCA()));
}
```
### Setter definition
```C++
JSC_DEFINE_CUSTOM_SETTER(jsImportMetaObjectSetter_require, (JSGlobalObject * jsGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName propertyName))
{
ImportMetaObject* thisObject = jsDynamicCast<ImportMetaObject*>(JSValue::decode(thisValue));
if (UNLIKELY(!thisObject))
return false;
JSValue value = JSValue::decode(encodedValue);
if (!value.isCell()) {
// TODO:
return true;
}
thisObject->requireProperty.set(thisObject->vm(), thisObject, value.asCell());
return true;
}
```
### Function definition
```C++
JSC_DEFINE_HOST_FUNCTION(jsX509CertificateProtoFuncToJSON, (JSGlobalObject * globalObject, CallFrame* callFrame))
{
VM& vm = globalObject->vm();
auto scope = DECLARE_THROW_SCOPE(vm);
auto *thisObject = jsDynamicCast<MyClassT*>(callFrame->thisValue());
if (UNLIKELY(!thisObject)) {
Bun::throwThisTypeError(*globalObject, scope, "MyClass"_s, "myFunctionName"_s);
return {};
}
return JSValue::encode(functionThatReturnsJSValue(vm, globalObject, thisObject));
}
```
### Constructor definition
```C++
JSC_DECLARE_HOST_FUNCTION(callStats);
JSC_DECLARE_HOST_FUNCTION(constructStats);
class JSStatsConstructor final : public JSC::InternalFunction {
public:
using Base = JSC::InternalFunction;
static constexpr unsigned StructureFlags = Base::StructureFlags;
static JSStatsConstructor* create(JSC::VM& vm, JSC::Structure* structure, JSC::JSObject* prototype)
{
JSStatsConstructor* constructor = new (NotNull, JSC::allocateCell<JSStatsConstructor>(vm)) JSStatsConstructor(vm, structure);
constructor->finishCreation(vm, prototype);
return constructor;
}
DECLARE_INFO;
template<typename CellType, JSC::SubspaceAccess>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm)
{
return &vm.internalFunctionSpace();
}
static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype)
{
return JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::InternalFunctionType, StructureFlags), info());
}
private:
JSStatsConstructor(JSC::VM& vm, JSC::Structure* structure)
: Base(vm, structure, callStats, constructStats)
{
}
void finishCreation(JSC::VM& vm, JSC::JSObject* prototype)
{
Base::finishCreation(vm, 0, "Stats"_s);
putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, JSC::PropertyAttribute::DontEnum | JSC::PropertyAttribute::DontDelete | JSC::PropertyAttribute::ReadOnly);
}
};
```
### Structure caching
If there's a class, prototype, and constructor:
1. Add the `JSC::LazyClassStructure` to [ZigGlobalObject.h](mdc:src/bun.js/bindings/ZigGlobalObject.h)
2. Initialize the class structure in [ZigGlobalObject.cpp](mdc:src/bun.js/bindings/ZigGlobalObject.cpp) in `void GlobalObject::finishCreation(VM& vm)`
3. Visit the class structure in visitChildren in [ZigGlobalObject.cpp](mdc:src/bun.js/bindings/ZigGlobalObject.cpp) in `void GlobalObject::visitChildrenImpl`
```c++#ZigGlobalObject.cpp
void GlobalObject::finishCreation(VM& vm) {
// ...
m_JSStatsBigIntClassStructure.initLater(
[](LazyClassStructure::Initializer& init) {
// Call the function to initialize our class structure.
Bun::initJSBigIntStatsClassStructure(init);
});
```
Then, implement the function that creates the structure:
```c++
void setupX509CertificateClassStructure(LazyClassStructure::Initializer& init)
{
auto* prototypeStructure = JSX509CertificatePrototype::createStructure(init.vm, init.global, init.global->objectPrototype());
auto* prototype = JSX509CertificatePrototype::create(init.vm, init.global, prototypeStructure);
auto* constructorStructure = JSX509CertificateConstructor::createStructure(init.vm, init.global, init.global->functionPrototype());
auto* constructor = JSX509CertificateConstructor::create(init.vm, init.global, constructorStructure, prototype);
auto* structure = JSX509Certificate::createStructure(init.vm, init.global, prototype);
init.setPrototype(prototype);
init.setStructure(structure);
init.setConstructor(constructor);
}
```
If there's only a class, use `JSC::LazyProperty<JSGlobalObject, Structure>` instead of `JSC::LazyClassStructure`:
1. Add the `JSC::LazyProperty<JSGlobalObject, Structure>` to @ZigGlobalObject.h
2. Initialize the class structure in @ZigGlobalObject.cpp in `void GlobalObject::finishCreation(VM& vm)`
3. Visit the lazy property in visitChildren in @ZigGlobalObject.cpp in `void GlobalObject::visitChildrenImpl`
void GlobalObject::finishCreation(VM& vm) {
// ...
this.m_myLazyProperty.initLater([](const JSC::LazyProperty<JSC::JSGlobalObject, JSC::Structure>::Initializer& init) {
init.set(Bun::initMyStructure(init.vm, reinterpret_cast<Zig::GlobalObject\*>(init.owner)));
});
```
Then, implement the function that creates the structure:
```c++
Structure* setupX509CertificateStructure(JSC::VM &vm, Zig::GlobalObject* globalObject)
{
// If there is a prototype:
auto* prototypeStructure = JSX509CertificatePrototype::createStructure(init.vm, init.global, init.global->objectPrototype());
auto* prototype = JSX509CertificatePrototype::create(init.vm, init.global, prototypeStructure);
// If there is no prototype or it only has
auto* structure = JSX509Certificate::createStructure(init.vm, init.global, prototype);
init.setPrototype(prototype);
init.setStructure(structure);
init.setConstructor(constructor);
}
```
Then, use the structure by calling `globalObject.m_myStructureName.get(globalObject)`
```C++
JSC_DEFINE_HOST_FUNCTION(x509CertificateConstructorConstruct, (JSGlobalObject * globalObject, CallFrame* callFrame))
{
VM& vm = globalObject->vm();
auto scope = DECLARE_THROW_SCOPE(vm);
if (!callFrame->argumentCount()) {
Bun::throwError(globalObject, scope, ErrorCode::ERR_MISSING_ARGS, "X509Certificate constructor requires at least one argument"_s);
return {};
}
JSValue arg = callFrame->uncheckedArgument(0);
if (!arg.isCell()) {
Bun::throwError(globalObject, scope, ErrorCode::ERR_INVALID_ARG_TYPE, "X509Certificate constructor argument must be a Buffer, TypedArray, or string"_s);
return {};
}
auto* zigGlobalObject = defaultGlobalObject(globalObject);
Structure* structure = zigGlobalObject->m_JSX509CertificateClassStructure.get(zigGlobalObject);
JSValue newTarget = callFrame->newTarget();
if (UNLIKELY(zigGlobalObject->m_JSX509CertificateClassStructure.constructor(zigGlobalObject) != newTarget)) {
auto scope = DECLARE_THROW_SCOPE(vm);
if (!newTarget) {
throwTypeError(globalObject, scope, "Class constructor X509Certificate cannot be invoked without 'new'"_s);
return {};
}
auto* functionGlobalObject = defaultGlobalObject(getFunctionRealm(globalObject, newTarget.getObject()));
RETURN_IF_EXCEPTION(scope, {});
structure = InternalFunction::createSubclassStructure(globalObject, newTarget.getObject(), functionGlobalObject->NodeVMScriptStructure());
RETURN_IF_EXCEPTION(scope, {});
}
return JSValue::encode(createX509Certificate(vm, globalObject, structure, arg));
}
```
### Expose to Zig
To expose the constructor to zig:
```c++
extern "C" JSC::EncodedJSValue Bun__JSBigIntStatsObjectConstructor(Zig::GlobalObject* globalobject)
{
return JSValue::encode(globalobject->m_JSStatsBigIntClassStructure.constructor(globalobject));
}
```
Zig:
```zig
extern "c" fn Bun__JSBigIntStatsObjectConstructor(*JSC.JSGlobalObject) JSC.JSValue;
pub const getBigIntStatsConstructor = Bun__JSBigIntStatsObjectConstructor;
```
To create an object (instance) of a JS class defined in C++ from Zig, follow the \_\_toJS convention like this:
```c++
// X509* is whatever we need to create the object
extern "C" EncodedJSValue Bun__X509__toJS(Zig::GlobalObject* globalObject, X509* cert)
{
// ... implementation details
auto* structure = globalObject->m_JSX509CertificateClassStructure.get(globalObject);
return JSValue::encode(JSX509Certificate::create(globalObject->vm(), structure, globalObject, WTFMove(cert)));
}
```
And from Zig:
```zig
const X509 = opaque {
// ... class
extern fn Bun__X509__toJS(*JSC.JSGlobalObject, *X509) JSC.JSValue;
pub fn toJS(this: *X509, globalObject: *JSC.JSGlobalObject) JSC.JSValue {
return Bun__X509__toJS(globalObject, this);
}
};
```

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# Registering Functions, Objects, and Modules in Bun
This guide documents the process of adding new functionality to the Bun global object and runtime.
## Overview
Bun's architecture exposes functionality to JavaScript through a set of carefully registered functions, objects, and modules. Most core functionality is implemented in Zig, with JavaScript bindings that make these features accessible to users.
There are several key ways to expose functionality in Bun:
1. **Global Functions**: Direct methods on the `Bun` object (e.g., `Bun.serve()`)
2. **Getter Properties**: Lazily initialized properties on the `Bun` object (e.g., `Bun.sqlite`)
3. **Constructor Classes**: Classes available through the `Bun` object (e.g., `Bun.ValkeyClient`)
4. **Global Modules**: Modules that can be imported directly (e.g., `import {X} from "bun:*"`)
## The Registration Process
Adding new functionality to Bun involves several coordinated steps across multiple files:
### 1. Implement the Core Functionality in Zig
First, implement your feature in Zig, typically in its own directory in `src/`. Examples:
- `src/valkey/` for Redis/Valkey client
- `src/semver/` for SemVer functionality
- `src/smtp/` for SMTP client
### 2. Create JavaScript Bindings
Create bindings that expose your Zig functionality to JavaScript:
- Create a class definition file (e.g., `js_bindings.classes.ts`) to define the JavaScript interface
- Implement `JSYourFeature` struct in a file like `js_your_feature.zig`
Example from a class definition file:
```typescript
// Example from a .classes.ts file
import { define } from "../../codegen/class-definitions";
export default [
define({
name: "YourFeature",
construct: true,
finalize: true,
hasPendingActivity: true,
memoryCost: true,
klass: {},
JSType: "0b11101110",
proto: {
yourMethod: {
fn: "yourZigMethod",
length: 1,
},
property: {
getter: "getProperty",
},
},
values: ["cachedValues"],
}),
];
```
### 3. Register with BunObject in `src/bun.js/bindings/BunObject+exports.h`
Add an entry to the `FOR_EACH_GETTER` macro:
```c
// In BunObject+exports.h
#define FOR_EACH_GETTER(macro) \
macro(CSRF) \
macro(CryptoHasher) \
... \
macro(YourFeature) \
```
### 4. Create a Getter Function in `src/bun.js/api/BunObject.zig`
Implement a getter function in `BunObject.zig` that returns your feature:
```zig
// In BunObject.zig
pub const YourFeature = toJSGetter(Bun.getYourFeatureConstructor);
// In the exportAll() function:
@export(&BunObject.YourFeature, .{ .name = getterName("YourFeature") });
```
### 5. Implement the Getter Function in a Relevant Zig File
Implement the function that creates your object:
```zig
// In your main module file (e.g., src/your_feature/your_feature.zig)
pub fn getYourFeatureConstructor(globalThis: *JSC.JSGlobalObject, _: *JSC.JSObject) JSC.JSValue {
return JSC.API.YourFeature.getConstructor(globalThis);
}
```
### 6. Add to Build System
Ensure your files are included in the build system by adding them to the appropriate targets.
## Example: Adding a New Module
Here's a comprehensive example of adding a hypothetical SMTP module:
1. Create implementation files in `src/smtp/`:
- `index.zig`: Main entry point that exports everything
- `SmtpClient.zig`: Core SMTP client implementation
- `js_smtp.zig`: JavaScript bindings
- `js_bindings.classes.ts`: Class definition
2. Define your JS class in `js_bindings.classes.ts`:
```typescript
import { define } from "../../codegen/class-definitions";
export default [
define({
name: "EmailClient",
construct: true,
finalize: true,
hasPendingActivity: true,
configurable: false,
memoryCost: true,
klass: {},
JSType: "0b11101110",
proto: {
send: {
fn: "send",
length: 1,
},
verify: {
fn: "verify",
length: 0,
},
close: {
fn: "close",
length: 0,
},
},
values: ["connectionPromise"],
}),
];
```
3. Add getter to `BunObject+exports.h`:
```c
#define FOR_EACH_GETTER(macro) \
macro(CSRF) \
... \
macro(SMTP) \
```
4. Add getter function to `BunObject.zig`:
```zig
pub const SMTP = toJSGetter(Bun.getSmtpConstructor);
// In exportAll:
@export(&BunObject.SMTP, .{ .name = getterName("SMTP") });
```
5. Implement getter in your module:
```zig
pub fn getSmtpConstructor(globalThis: *JSC.JSGlobalObject, _: *JSC.JSObject) JSC.JSValue {
return JSC.API.JSEmailClient.getConstructor(globalThis);
}
```
## Best Practices
1. **Follow Naming Conventions**: Align your naming with existing patterns
2. **Reference Existing Modules**: Study similar modules like Valkey or S3Client for guidance
3. **Memory Management**: Be careful with memory management and reference counting
4. **Error Handling**: Use `bun.JSError!JSValue` for proper error propagation
5. **Documentation**: Add JSDoc comments to your JavaScript bindings
6. **Testing**: Add tests for your new functionality
## Common Gotchas
- Be sure to handle reference counting properly with `ref()`/`deref()`
- Always implement proper cleanup in `deinit()` and `finalize()`
- For network operations, manage socket lifetimes correctly
- Use `JSC.Codegen` correctly to generate necessary binding code
## Related Files
- `src/bun.js/bindings/BunObject+exports.h`: Registration of getters and functions
- `src/bun.js/api/BunObject.zig`: Implementation of getters and object creation
- `src/bun.js/api/BunObject.classes.ts`: Class definitions
- `.cursor/rules/zig-javascriptcore-classes.mdc`: More details on class bindings
## Additional Resources
For more detailed information on specific topics:
- See `zig-javascriptcore-classes.mdc` for details on creating JS class bindings
- Review existing modules like `valkey`, `sqlite`, or `s3` for real-world examples

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---
description: Writing tests for Bun
globs:
---
# Writing tests for Bun
## Where tests are found
You'll find all of Bun's tests in the `test/` directory.
* `test/`
* `cli/` - CLI command tests, like `bun install` or `bun init`
* `js/` - JavaScript & TypeScript tests
* `bun/` - `Bun` APIs tests, separated by category, for example: `glob/` for `Bun.Glob` tests
* `node/` - Node.js module tests, separated by module, for example: `assert/` for `node:assert` tests
* `test/` - Vendored Node.js tests, taken from the Node.js repository (does not conform to Bun's test style)
* `web/` - Web API tests, separated by category, for example: `fetch/` for `Request` and `Response` tests
* `third_party/` - npm package tests, to validate that basic usage works in Bun
* `napi/` - N-API tests
* `v8/` - V8 C++ API tests
* `bundler/` - Bundler, transpiler, CSS, and `bun build` tests
* `regression/issue/[number]` - Regression tests, always make one when fixing a particular issue
## How tests are written
Bun's tests are written as JavaScript and TypeScript files with the Jest-style APIs, like `test`, `describe`, and `expect`. They are tested using Bun's own test runner, `bun test`.
```js
import { describe, test, expect } from "bun:test";
import assert, { AssertionError } from "assert";
describe("assert(expr)", () => {
test.each([true, 1, "foo"])(`assert(%p) does not throw`, expr => {
expect(() => assert(expr)).not.toThrow();
});
test.each([false, 0, "", null, undefined])(`assert(%p) throws`, expr => {
expect(() => assert(expr)).toThrow(AssertionError);
});
});
```
## Testing conventions
* See `test/harness.ts` for common test utilities and helpers
* Be rigorous and test for edge-cases and unexpected inputs
* Use data-driven tests, e.g. `test.each`, to reduce boilerplate when possible
* When you need to test Bun as a CLI, use the following pattern:
```js
import { test, expect } from "bun:test";
import { spawn } from "bun";
import { bunExe, bunEnv } from "harness";
test("bun --version", async () => {
const { exited, stdout: stdoutStream, stderr: stderrStream } = spawn({
cmd: [bunExe(), "--version"],
env: bunEnv,
stdout: "pipe",
stderr: "pipe",
});
const [ exitCode, stdout, stderr ] = await Promise.all([
exited,
new Response(stdoutStream).text(),
new Response(stderrStream).text(),
]);
expect({ exitCode, stdout, stderr }).toMatchObject({
exitCode: 0,
stdout: expect.stringContaining(Bun.version),
stderr: "",
});
});
```
## Before writing a test
* If you are fixing a bug, write the test first and make sure it fails (as expected) with the canary version of Bun
* If you are fixing a Node.js compatibility bug, create a throw-away snippet of code and test that it works as you expect in Node.js, then that it fails (as expected) with the canary version of Bun
* When the expected behaviour is ambigious, defer to matching what happens in Node.js
* Always attempt to find related tests in an existing test file before creating a new test file

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---
description: How Zig works with JavaScriptCore bindings generator
globs:
alwaysApply: false
---
# Bun's JavaScriptCore Class Bindings Generator
This document explains how Bun's class bindings generator works to bridge Zig and JavaScript code through JavaScriptCore (JSC).
## Architecture Overview
Bun's binding system creates a seamless bridge between JavaScript and Zig, allowing Zig implementations to be exposed as JavaScript classes. The system has several key components:
1. **Zig Implementation** (.zig files)
2. **JavaScript Interface Definition** (.classes.ts files)
3. **Generated Code** (C++/Zig files that connect everything)
## Class Definition Files
### JavaScript Interface (.classes.ts)
The `.classes.ts` files define the JavaScript API using a declarative approach:
```typescript
// Example: encoding.classes.ts
define({
name: "TextDecoder",
constructor: true,
JSType: "object",
finalize: true,
proto: {
decode: {
// Function definition
args: 1,
},
encoding: {
// Getter with caching
getter: true,
cache: true,
},
fatal: {
// Read-only property
getter: true,
},
ignoreBOM: {
// Read-only property
getter: true,
},
},
});
```
Each class definition specifies:
- The class name
- Whether it has a constructor
- JavaScript type (object, function, etc.)
- Properties and methods in the `proto` field
- Caching strategy for properties
- Finalization requirements
### Zig Implementation (.zig)
The Zig files implement the native functionality:
```zig
// Example: TextDecoder.zig
pub const TextDecoder = struct {
// Expose generated bindings as `js` namespace with trait conversion methods
pub const js = JSC.Codegen.JSTextDecoder;
pub const toJS = js.toJS;
pub const fromJS = js.fromJS;
pub const fromJSDirect = js.fromJSDirect;
// Internal state
encoding: []const u8,
fatal: bool,
ignoreBOM: bool,
// Constructor implementation - note use of globalObject
pub fn constructor(
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!*TextDecoder {
// Implementation
return bun.new(TextDecoder, .{
// Fields
});
}
// Prototype methods - note return type includes JSError
pub fn decode(
this: *TextDecoder,
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!JSC.JSValue {
// Implementation
}
// Getters
pub fn getEncoding(this: *TextDecoder, globalObject: *JSGlobalObject) JSC.JSValue {
return JSC.JSValue.createStringFromUTF8(globalObject, this.encoding);
}
pub fn getFatal(this: *TextDecoder, globalObject: *JSGlobalObject) JSC.JSValue {
return JSC.JSValue.jsBoolean(this.fatal);
}
// Cleanup - note standard pattern of using deinit/deref
fn deinit(this: *TextDecoder) void {
// Release any retained resources
// Free the pointer at the end.
bun.destroy(this);
}
// Finalize - called by JS garbage collector. This should call deinit, or deref if reference counted.
pub fn finalize(this: *TextDecoder) void {
this.deinit();
}
};
```
Key components in the Zig file:
- The struct containing native state
- `pub const js = JSC.Codegen.JS<ClassName>` to include generated code
- Constructor and methods using `bun.JSError!JSValue` return type for proper error handling
- Consistent use of `globalObject` parameter name instead of `ctx`
- Methods matching the JavaScript interface
- Getters/setters for properties
- Proper resource cleanup pattern with `deinit()` and `finalize()`
- Update `src/bun.js/bindings/generated_classes_list.zig` to include the new class
## Code Generation System
The binding generator produces C++ code that connects JavaScript and Zig:
1. **JSC Class Structure**: Creates C++ classes for the JS object, prototype, and constructor
2. **Memory Management**: Handles GC integration through JSC's WriteBarrier
3. **Method Binding**: Connects JS function calls to Zig implementations
4. **Type Conversion**: Converts between JS values and Zig types
5. **Property Caching**: Implements the caching system for properties
The generated C++ code includes:
- A JSC wrapper class (`JSTextDecoder`)
- A prototype class (`JSTextDecoderPrototype`)
- A constructor function (`JSTextDecoderConstructor`)
- Function bindings (`TextDecoderPrototype__decodeCallback`)
- Property getters/setters (`TextDecoderPrototype__encodingGetterWrap`)
## CallFrame Access
The `CallFrame` object provides access to JavaScript execution context:
```zig
pub fn decode(
this: *TextDecoder,
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame
) bun.JSError!JSC.JSValue {
// Get arguments
const input = callFrame.argument(0);
const options = callFrame.argument(1);
// Get this value
const thisValue = callFrame.thisValue();
// Implementation with error handling
if (input.isUndefinedOrNull()) {
return globalObject.throw("Input cannot be null or undefined", .{});
}
// Return value or throw error
return JSC.JSValue.jsString(globalObject, "result");
}
```
CallFrame methods include:
- `argument(i)`: Get the i-th argument
- `argumentCount()`: Get the number of arguments
- `thisValue()`: Get the `this` value
- `callee()`: Get the function being called
## Property Caching and GC-Owned Values
The `cache: true` option in property definitions enables JSC's WriteBarrier to efficiently store values:
```typescript
encoding: {
getter: true,
cache: true, // Enable caching
}
```
### C++ Implementation
In the generated C++ code, caching uses JSC's WriteBarrier:
```cpp
JSC_DEFINE_CUSTOM_GETTER(TextDecoderPrototype__encodingGetterWrap, (...)) {
auto& vm = JSC::getVM(lexicalGlobalObject);
Zig::GlobalObject *globalObject = reinterpret_cast<Zig::GlobalObject*>(lexicalGlobalObject);
auto throwScope = DECLARE_THROW_SCOPE(vm);
JSTextDecoder* thisObject = jsCast<JSTextDecoder*>(JSValue::decode(encodedThisValue));
JSC::EnsureStillAliveScope thisArg = JSC::EnsureStillAliveScope(thisObject);
// Check for cached value and return if present
if (JSValue cachedValue = thisObject->m_encoding.get())
return JSValue::encode(cachedValue);
// Get value from Zig implementation
JSC::JSValue result = JSC::JSValue::decode(
TextDecoderPrototype__getEncoding(thisObject->wrapped(), globalObject)
);
RETURN_IF_EXCEPTION(throwScope, {});
// Store in cache for future access
thisObject->m_encoding.set(vm, thisObject, result);
RELEASE_AND_RETURN(throwScope, JSValue::encode(result));
}
```
### Zig Accessor Functions
For each cached property, the generator creates Zig accessor functions that allow Zig code to work with these GC-owned values:
```zig
// External function declarations
extern fn TextDecoderPrototype__encodingSetCachedValue(JSC.JSValue, *JSC.JSGlobalObject, JSC.JSValue) callconv(JSC.conv) void;
extern fn TextDecoderPrototype__encodingGetCachedValue(JSC.JSValue) callconv(JSC.conv) JSC.JSValue;
/// `TextDecoder.encoding` setter
/// This value will be visited by the garbage collector.
pub fn encodingSetCached(thisValue: JSC.JSValue, globalObject: *JSC.JSGlobalObject, value: JSC.JSValue) void {
JSC.markBinding(@src());
TextDecoderPrototype__encodingSetCachedValue(thisValue, globalObject, value);
}
/// `TextDecoder.encoding` getter
/// This value will be visited by the garbage collector.
pub fn encodingGetCached(thisValue: JSC.JSValue) ?JSC.JSValue {
JSC.markBinding(@src());
const result = TextDecoderPrototype__encodingGetCachedValue(thisValue);
if (result == .zero)
return null;
return result;
}
```
### Benefits of GC-Owned Values
This system provides several key benefits:
1. **Automatic Memory Management**: The JavaScriptCore GC tracks and manages these values
2. **Proper Garbage Collection**: The WriteBarrier ensures values are properly visited during GC
3. **Consistent Access**: Zig code can easily get/set these cached JS values
4. **Performance**: Cached values avoid repeated computation or serialization
### Use Cases
GC-owned cached values are particularly useful for:
1. **Computed Properties**: Store expensive computation results
2. **Lazily Created Objects**: Create objects only when needed, then cache them
3. **References to Other Objects**: Store references to other JS objects that need GC tracking
4. **Memoization**: Cache results based on input parameters
The WriteBarrier mechanism ensures that any JS values stored in this way are properly tracked by the garbage collector.
## Memory Management and Finalization
The binding system handles memory management across the JavaScript/Zig boundary:
1. **Object Creation**: JavaScript `new TextDecoder()` creates both a JS wrapper and a Zig struct
2. **Reference Tracking**: JSC's GC tracks all JS references to the object
3. **Finalization**: When the JS object is collected, the finalizer releases Zig resources
Bun uses a consistent pattern for resource cleanup:
```zig
// Resource cleanup method - separate from finalization
pub fn deinit(this: *TextDecoder) void {
// Release resources like strings
this._encoding.deref(); // String deref pattern
// Free any buffers
if (this.buffer) |buffer| {
bun.default_allocator.free(buffer);
}
}
// Called by the GC when object is collected
pub fn finalize(this: *TextDecoder) void {
JSC.markBinding(@src()); // For debugging
this.deinit(); // Clean up resources
bun.default_allocator.destroy(this); // Free the object itself
}
```
Some objects that hold references to other JS objects use `.deref()` instead:
```zig
pub fn finalize(this: *SocketAddress) void {
JSC.markBinding(@src());
this._presentation.deref(); // Release references
this.destroy();
}
```
## Error Handling with JSError
Bun uses `bun.JSError!JSValue` return type for proper error handling:
```zig
pub fn decode(
this: *TextDecoder,
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame
) bun.JSError!JSC.JSValue {
// Throwing an error
if (callFrame.argumentCount() < 1) {
return globalObject.throw("Missing required argument", .{});
}
// Or returning a success value
return JSC.JSValue.jsString(globalObject, "Success!");
}
```
This pattern allows Zig functions to:
1. Return JavaScript values on success
2. Throw JavaScript exceptions on error
3. Propagate errors automatically through the call stack
## Type Safety and Error Handling
The binding system includes robust error handling:
```cpp
// Example of type checking in generated code
JSTextDecoder* thisObject = jsDynamicCast<JSTextDecoder*>(callFrame->thisValue());
if (UNLIKELY(!thisObject)) {
scope.throwException(lexicalGlobalObject,
Bun::createInvalidThisError(lexicalGlobalObject, callFrame->thisValue(), "TextDecoder"_s));
return {};
}
```
## Prototypal Inheritance
The binding system creates proper JavaScript prototype chains:
1. **Constructor**: JSTextDecoderConstructor with standard .prototype property
2. **Prototype**: JSTextDecoderPrototype with methods and properties
3. **Instances**: Each JSTextDecoder instance with **proto** pointing to prototype
This ensures JavaScript inheritance works as expected:
```cpp
// From generated code
void JSTextDecoderConstructor::finishCreation(VM& vm, JSC::JSGlobalObject* globalObject, JSTextDecoderPrototype* prototype)
{
Base::finishCreation(vm, 0, "TextDecoder"_s, PropertyAdditionMode::WithoutStructureTransition);
// Set up the prototype chain
putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, PropertyAttribute::DontEnum | PropertyAttribute::DontDelete | PropertyAttribute::ReadOnly);
ASSERT(inherits(info()));
}
```
## Performance Considerations
The binding system is optimized for performance:
1. **Direct Pointer Access**: JavaScript objects maintain a direct pointer to Zig objects
2. **Property Caching**: WriteBarrier caching avoids repeated native calls for stable properties
3. **Memory Management**: JSC garbage collection integrated with Zig memory management
4. **Type Conversion**: Fast paths for common JavaScript/Zig type conversions
## Creating a New Class Binding
To create a new class binding in Bun:
1. **Define the class interface** in a `.classes.ts` file:
```typescript
define({
name: "MyClass",
constructor: true,
finalize: true,
proto: {
myMethod: {
args: 1,
},
myProperty: {
getter: true,
cache: true,
},
},
});
```
2. **Implement the native functionality** in a `.zig` file:
```zig
pub const MyClass = struct {
// Generated bindings
pub const js = JSC.Codegen.JSMyClass;
pub const toJS = js.toJS;
pub const fromJS = js.fromJS;
pub const fromJSDirect = js.fromJSDirect;
// State
value: []const u8,
pub const new = bun.TrivialNew(@This());
// Constructor
pub fn constructor(
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!*MyClass {
const arg = callFrame.argument(0);
// Implementation
}
// Method
pub fn myMethod(
this: *MyClass,
globalObject: *JSGlobalObject,
callFrame: *JSC.CallFrame,
) bun.JSError!JSC.JSValue {
// Implementation
}
// Getter
pub fn getMyProperty(this: *MyClass, globalObject: *JSGlobalObject) JSC.JSValue {
return JSC.JSValue.jsString(globalObject, this.value);
}
// Resource cleanup
pub fn deinit(this: *MyClass) void {
// Clean up resources
}
pub fn finalize(this: *MyClass) void {
this.deinit();
bun.destroy(this);
}
};
```
3. **The binding generator** creates all necessary C++ and Zig glue code to connect JavaScript and Zig, including:
- C++ class definitions
- Method and property bindings
- Memory management utilities
- GC integration code
## Generated Code Structure
The binding generator produces several components:
### 1. C++ Classes
For each Zig class, the system generates:
- **JS<Class>**: Main wrapper that holds a pointer to the Zig object (`JSTextDecoder`)
- **JS<Class>Prototype**: Contains methods and properties (`JSTextDecoderPrototype`)
- **JS<Class>Constructor**: Implementation of the JavaScript constructor (`JSTextDecoderConstructor`)
### 2. C++ Methods and Properties
- **Method Callbacks**: `TextDecoderPrototype__decodeCallback`
- **Property Getters/Setters**: `TextDecoderPrototype__encodingGetterWrap`
- **Initialization Functions**: `finishCreation` methods for setting up the class
### 3. Zig Bindings
- **External Function Declarations**:
```zig
extern fn TextDecoderPrototype__decode(*TextDecoder, *JSC.JSGlobalObject, *JSC.CallFrame) callconv(JSC.conv) JSC.EncodedJSValue;
```
- **Cached Value Accessors**:
```zig
pub fn encodingGetCached(thisValue: JSC.JSValue) ?JSC.JSValue { ... }
pub fn encodingSetCached(thisValue: JSC.JSValue, globalObject: *JSC.JSGlobalObject, value: JSC.JSValue) void { ... }
```
- **Constructor Helpers**:
```zig
pub fn create(globalObject: *JSC.JSGlobalObject) bun.JSError!JSC.JSValue { ... }
```
### 4. GC Integration
- **Memory Cost Calculation**: `estimatedSize` method
- **Child Visitor Methods**: `visitChildrenImpl` and `visitAdditionalChildren`
- **Heap Analysis**: `analyzeHeap` for debugging memory issues
This architecture makes it possible to implement high-performance native functionality in Zig while exposing a clean, idiomatic JavaScript API to users.