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https://github.com/oven-sh/bun
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## Summary
Adds comprehensive support to `generate-classes.ts` for JavaScript
classes that need both named WriteBarrier members (like callbacks) and a
dynamic array of JSValues, all properly tracked by the garbage
collector. This replaces error-prone manual `protect()/unprotect()`
calls with proper GC integration.
## Motivation
The shell interpreter was using `JSValue.protect()/unprotect()` to keep
JavaScript objects alive, which caused memory leaks when cleanup paths
didn't properly unprotect values. This is a common pattern that needed a
better solution.
## What Changed
### Code Generator (`generate-classes.ts`)
When a class has both `values: ["resolve", "reject"]` and `valuesArray:
true`:
**Generated C++ class gets:**
- `WTF::FixedVector<JSC::WriteBarrier<JSC::Unknown>> jsvalueArray`
member for dynamic array
- Individual `JSC::WriteBarrier<JSC::Unknown> m_resolve, m_reject`
members for named values
- 4 `create()` overloads covering all combinations:
1. Basic: `create(vm, globalObject, structure, ptr)`
2. Array only: `create(..., FixedVector<WriteBarrier<Unknown>>&&)`
3. Named values: `create(..., JSValue resolve, JSValue reject)`
4. Both: `create(..., FixedVector&&, JSValue resolve, JSValue reject)`
**Constructor overloads using `WriteBarrierEarlyInit`:**
```cpp
JSShellInterpreter(VM& vm, Structure* structure, void* ptr,
JSValue resolve, JSValue reject)
: Base(vm, structure)
, m_resolve(resolve, JSC::WriteBarrierEarlyInit) // ← Key technique
, m_reject(reject, JSC::WriteBarrierEarlyInit)
{
m_ctx = ptr;
}
```
The `WriteBarrierEarlyInit` tag allows initializing WriteBarriers in the
constructor initializer list before the object is fully constructed,
which is required for proper GC integration.
**Extern C bridge functions:**
- `TypeName__createWithValues(globalObject, ptr, markedArgumentBuffer*)`
- `TypeName__createWithInitialValues(globalObject, ptr, resolve,
reject)`
- `TypeName__createWithValuesAndInitialValues(globalObject, ptr,
buffer*, resolve, reject)`
**Zig convenience wrappers:**
- `toJSWithValues(this, globalObject, markedArgumentBuffer)`
- `toJSWithInitialValues(this, globalObject, resolve, reject)`
- `toJSWithValuesAndInitialValues(this, globalObject, buffer, resolve,
reject)`
### Shell Interpreter Memory Leak Fix
**Before:**
```zig
const js_value = JSShellInterpreter.toJS(interpreter, globalThis);
resolve.protect(); // Manual reference counting
reject.protect();
// ... later in cleanup ...
resolve.unprotect(); // Easy to forget/miss in error paths
reject.unprotect();
```
**After:**
```zig
const js_value = Bun__createShellInterpreter(
globalThis,
interpreter,
parsed_shell_script,
resolve, // Stored with WriteBarrierEarlyInit
reject, // GC tracks automatically
);
// No manual memory management needed!
```
### Supporting Changes
- Added `MarkedArgumentBuffer.wrap()` helper in Zig for safe
MarkedArgumentBuffer usage
- Created `ShellBindings.cpp` with `Bun__createShellInterpreter()` using
the new API
- Removed all `protect()/unprotect()` calls from shell interpreter
- Applied pattern to both `ShellInterpreter` and `ShellArgs` classes
## Benefits
1. **No memory leaks**: GC tracks all references automatically
2. **Safer**: Cannot forget to unprotect values
3. **Cleaner code**: No manual reference counting
4. **Reusable**: Pattern works for any class needing to store JSValues
5. **Performance**: Same cost as manual protect/unprotect but safer
## Testing
Existing shell tests verify the functionality. The pattern is already
used throughout JavaScriptCore for similar cases (see
`JSWrappingFunction`, `AsyncContextFrame`, `JSModuleMock`, etc.)
## When to Use This Pattern
Use `values` + `valuesArray` + `WriteBarrierEarlyInit` when:
- Your C++ class needs to keep JavaScript values alive
- You have both known named callbacks AND dynamic arrays of values
- You want the GC to track references instead of manual
protect/unprotect
- Your class extends `JSDestructibleObject`
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Tests
Finding tests
Tests are located in the test/ directory and are organized using the following structure:
test/js/- tests for JavaScript APIs.cli/- tests for commands, configs, and stdout.bundler/- tests for the transpiler/bundler.regression/- tests that reproduce a specific issue.harness.ts- utility functions that can be imported from any test.
The tests in test/js/ directory are further categorized by the type of API.
test/js/bun/- tests forBun-specific APIs.node/- tests for Node.js APIs.web/- tests for Web APIs, likefetch().first_party/- tests for npm packages that are built-in, likeundici.third_party/- tests for npm packages that are not built-in, but are popular, likeesbuild.
Running tests
To run a test, use Bun's built-in test command: bun test.
bun test # Run all tests
bun test js/bun # Only run tests in a directory
bun test sqlite.test.ts # Only run a specific test
If you encounter lots of errors, try running bun install, then trying again.
Writing tests
Tests are written in TypeScript (preferred) or JavaScript using Jest's describe(), test(), and expect() APIs.
import { describe, test, expect } from "bun:test";
import { gcTick } from "harness";
describe("TextEncoder", () => {
test("can encode a string", async () => {
const encoder = new TextEncoder();
const actual = encoder.encode("bun");
await gcTick();
expect(actual).toBe(new Uint8Array([0x62, 0x75, 0x6E]));
});
});
If you are fixing a bug that was reported from a GitHub issue, remember to add a test in the test/regression/ directory.
// test/regression/issue/02005.test.ts
import { it, expect } from "bun:test";
it("regex literal should work with non-latin1", () => {
const text = "这是一段要替换的文字";
expect(text.replace(new RegExp("要替换"), "")).toBe("这是一段的文字");
expect(text.replace(/要替换/, "")).toBe("这是一段的文字");
});
In the future, a bot will automatically close or re-open issues when a regression is detected or resolved.
Zig tests
These tests live in various .zig files throughout Bun's codebase, leveraging Zig's builtin test keyword.
Currently, they're not run automatically nor is there a simple way to run all of them. We will make this better soon.
TypeScript
Test files should be written in TypeScript. The types in packages/bun-types should be updated to support all new APIs. Changes to the .d.ts files in packages/bun-types will be immediately reflected in test files; no build step is necessary.
Writing a test will often require using invalid syntax, e.g. when checking for errors when an invalid input is passed to a function. TypeScript provides a number of escape hatches here.
// @ts-expect-error- This should be your first choice. It tells TypeScript that the next line should fail typechecking.// @ts-ignore- Ignore the next line entirely.// @ts-nocheck- Put this at the top of the file to disable typechecking on the entire file. Useful for autogenerated test files, or when ignoring/disabling type checks an a per-line basis is too onerous.