## Summary
- Implement complete lowering of TC39 stage-3 standard ES decorators
(the non-legacy variant used when tsconfig has no
`experimentalDecorators`).
- Passes all 147 esbuild decorator tests and 22 additional Bun-specific
tests (191 total, 0 failures).
- Supports method, getter, setter, field, auto-accessor, private member,
and class decorators in both statement and expression positions, with
proper evaluation order, class binding semantics, and decorator
metadata.
Fixes#4122Fixes#20206Fixes#14529Fixes#6051
## What's implemented
| Feature | Details |
|---|---|
| Method/getter/setter decorators | Static and instance, public and
private |
| Field decorators | Initializer replacement + extra initializers via
`__runInitializers` |
| Auto-accessor (`accessor` keyword) | Lowered to WeakMap storage +
getter/setter pair |
| Private member decorators | WeakMap/WeakSet lowering with
`__privateGet`/`__privateSet` |
| Class decorators | Statement and expression positions |
| Class expression decorators | Comma-expression lowering (no IIFE) |
| Decorator metadata | `Symbol.metadata` support via
`__decoratorMetadata` |
| Evaluation order | All decorator expressions + computed keys evaluated
in source order per TC39 spec |
| Class binding semantics | Separate inner/outer class name bindings
(element vs class decorator closures) |
| Static block extraction | `this` replaced with class name ref when
moved to suffix |
| Computed property keys | Pre-evaluated into temp variables for correct
ordering |
## Runtime helpers
Added to `src/runtime.js` and registered in `src/runtime.zig`:
- `__decoratorStart(base)` — creates decorator context array
- `__decorateElement(array, flags, name, decorators, target, extra)` —
applies decorators to a class element
- `__decoratorMetadata(array, target)` — sets `Symbol.metadata` on the
class
- `__runInitializers(array, flags, self, value)` — runs
initializer/extra-initializer arrays
## Test plan
- [x] `bun bd test
test/bundler/transpiler/es-decorators-esbuild.test.ts` — **147/147
pass** (esbuild's full decorator test suite)
- [x] `bun bd test test/bundler/transpiler/es-decorators.test.ts` —
**22/22 pass**
- [x] `bun bd test test/bundler/transpiler/decorators.test.ts` — **22/22
pass** (legacy decorators still work)
- [x] E2E runtime verification of method, field, accessor, class,
private, and expression decorators
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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
Add `minify.unwrapCJSToESM` JS API option and `--unwrap-cjs-to-esm` CLI
flag to force CJS-to-ESM conversion for specific packages, eliminating
the `__commonJS` wrapper. Supports wildcard patterns (e.g. `"@scope/*"`).
User entries extend the default React family list.
Also removes the react/react-dom version check that gated conversion,
and fixes `packageName()` to handle scoped packages (`@scope/pkg`).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
## Summary
- Adds `--metafile-md` CLI option to `bun build` that generates a
markdown visualization of the module graph
- Designed to help Claude and other LLMs analyze bundle composition,
identify bloat, and understand dependency chains
- Reuses existing metafile JSON generation code as a post-processing
step
## Features
The generated markdown includes:
1. **Quick Summary** - Module counts, sizes, ESM/CJS breakdown,
output/input ratio
2. **Largest Input Files** - Sorted by size to identify potential bloat
3. **Entry Point Analysis** - Shows bundle size, exports, CSS bundles,
and bundled modules
4. **Dependency Chains** - Most commonly imported modules and reverse
dependencies
5. **Full Module Graph** - Complete import/export info for each module
6. **Raw Data for Searching** - Grep-friendly markers in code blocks:
- `[MODULE:]`, `[SIZE:]`, `[IMPORT:]`, `[IMPORTED_BY:]`
- `[ENTRY:]`, `[EXTERNAL:]`, `[NODE_MODULES:]`
## Usage
```bash
# Default filename (meta.md)
bun build entry.js --metafile-md --outdir=dist
# Custom filename
bun build entry.js --metafile-md=analysis.md --outdir=dist
# Both JSON and markdown
bun build entry.js --metafile=meta.json --metafile-md=meta.md --outdir=dist
```
## Example Output
See sample output: https://gist.github.com/example (will add)
## Test plan
- [x] Test default filename (`meta.md`)
- [x] Test custom filename
- [x] Test both `--metafile` and `--metafile-md` together
- [x] Test summary metrics
- [x] Test module format info (ESM/CJS)
- [x] Test external imports
- [x] Test exports list
- [x] Test bundled modules table
- [x] Test CSS bundle reference
- [x] Test import kinds (static, dynamic, require)
- [x] Test commonly imported modules
- [x] Test largest files sorting (bloat analysis)
- [x] Test output/input ratio
- [x] Test grep-friendly raw data section
- [x] Test entry point markers
- [x] Test external import markers
- [x] Test node_modules markers
All 17 new tests pass.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
## Summary
- Adds `Bun.JSON5.parse()` and `Bun.JSON5.stringify()` as built-in APIs
- Adds `.json5` file support in the module resolver and bundler
- Parser uses a scanner/parser split architecture with a labeled switch
pattern (like the YAML parser) — the scanner produces typed tokens, the
parser never touches source bytes directly
- 430+ tests covering the official JSON5 test suite, escape sequences,
numbers, comments, whitespace (including all Unicode whitespace types),
unquoted/reserved-word keys, unicode identifiers, deeply nested
structures, garbage input, error messages, and stringify behavior
<img width="659" height="610" alt="Screenshot 2026-01-25 at 12 19 57 AM"
src="https://github.com/user-attachments/assets/e300125a-f197-4cad-90ed-e867b6232a01"
/>
## Test plan
- [x] `bun bd test test/js/bun/json5/json5.test.ts` — 317 tests
- [x] `bun bd test test/js/bun/json5/json5-test-suite.test.ts` — 113
tests from the official JSON5 test suite
- [x] `bun bd test test/js/bun/resolve/json5/json5.test.js` — .json5
module resolution
closes#3175🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
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Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
## Summary
- Adds `import { feature } from "bun:bundle"` for compile-time feature
flag checking
- `feature("FLAG_NAME")` calls are replaced with `true`/`false` at
bundle time
- Enables dead-code elimination through `--feature=FLAG_NAME` CLI
argument
- Works in `bun build`, `bun run`, and `bun test`
- Available in both CLI and `Bun.build()` JavaScript API
## Usage
```ts
import { feature } from "bun:bundle";
if (feature("SUPER_SECRET")) {
console.log("Secret feature enabled!");
} else {
console.log("Normal mode");
}
```
### CLI
```bash
# Enable feature during build
bun build --feature=SUPER_SECRET index.ts
# Enable at runtime
bun run --feature=SUPER_SECRET index.ts
# Enable in tests
bun test --feature=SUPER_SECRET
```
### JavaScript API
```ts
await Bun.build({
entrypoints: ['./index.ts'],
outdir: './out',
features: ['SUPER_SECRET', 'ANOTHER_FLAG'],
});
```
## Implementation
- Added `bundler_feature_flags` (as `*const bun.StringSet`) to
`RuntimeFeatures` and `BundleOptions`
- Added `bundler_feature_flag_ref` to Parser struct to track the
`feature` import
- Handle `bun:bundle` import at parse time (similar to macros) - capture
ref, return empty statement
- Handle `feature()` calls in `e_call` visitor - replace with boolean
based on flags
- Wire feature flags through CLI arguments and `Bun.build()` API to
bundler options
- Added `features` option to `JSBundler.zig` for JavaScript API support
- Added TypeScript types in `bun.d.ts`
- Added documentation to `docs/bundler/index.mdx`
## Test plan
- [x] Basic feature flag enabled/disabled tests (both CLI and API
backends)
- [x] Multiple feature flags test
- [x] Dead code elimination verification tests
- [x] Error handling for invalid arguments
- [x] Runtime tests with `bun run --feature=FLAG`
- [x] Test runner tests with `bun test --feature=FLAG`
- [x] Aliased import tests (`import { feature as checkFeature }`)
- [x] Ternary operator DCE tests
- [x] Tests use `itBundled` with both `backend: "cli"` and `backend:
"api"`
🤖 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>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Alistair Smith <hi@alistair.sh>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
## Summary
By default, standalone executables no longer load `tsconfig.json` and
`package.json` at runtime. This improves startup performance and
prevents unexpected behavior from config files in the runtime
environment.
- Added `--compile-autoload-tsconfig` / `--no-compile-autoload-tsconfig`
CLI flags (default: false)
- Added `--compile-autoload-package-json` /
`--no-compile-autoload-package-json` CLI flags (default: false)
- Added `autoloadTsconfig` and `autoloadPackageJson` options to the
`Bun.build()` compile config
- Flags are stored in `StandaloneModuleGraph.Flags` and applied at
runtime boot
This follows the same pattern as the existing
`--compile-autoload-dotenv` and `--compile-autoload-bunfig` flags.
## Test plan
- [x] Added tests in `test/bundler/bundler_compile_autoload.test.ts`
- [x] Verified standalone executables work correctly with runtime config
files that differ from compile-time configs
- [x] Verified the new CLI flags are properly parsed and applied
- [x] Verified the JS API options work correctly
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
## Summary
Implements `--no-env-file` CLI flag and bunfig configuration options to
disable automatic `.env` file loading at runtime and in the bundler.
## Motivation
Users may want to disable automatic `.env` file loading for:
- Production environments where env vars are managed externally
- CI/CD pipelines where .env files should be ignored
- Testing scenarios where explicit env control is needed
- Security contexts where .env files should not be trusted
## Changes
### CLI Flag
- Added `--no-env-file` flag that disables loading of default .env files
- Still respects explicit `--env-file` arguments for intentional env
loading
### Bunfig Configuration
Added support for disabling .env loading via `bunfig.toml`:
- `env = false` - disables default .env file loading
- `env = null` - disables default .env file loading
- `env.file = false` - disables default .env file loading
- `env.file = null` - disables default .env file loading
### Implementation
- Added `disable_default_env_files` field to `api.TransformOptions` with
serialization support
- Added `disable_default_env_files` field to `options.Env` struct
- Implemented `loadEnvConfig` in bunfig parser to handle env
configuration
- Wired up flag throughout runtime and bundler code paths
- Preserved package.json script runner behavior (always skips default
.env files)
## Tests
Added comprehensive test suite (`test/cli/run/no-envfile.test.ts`) with
9 tests covering:
- `--no-env-file` flag with `.env`, `.env.local`,
`.env.development.local`
- Bunfig configurations: `env = false`, `env.file = false`, `env = true`
- `--no-env-file` with `-e` eval flag
- `--no-env-file` combined with `--env-file` (explicit files still load)
- Production mode behavior
All tests pass with debug bun and fail with system bun (as expected).
## Example Usage
```bash
# Disable all default .env files
bun --no-env-file index.js
# Disable defaults but load explicit file
bun --no-env-file --env-file .env.production index.js
# Disable via bunfig.toml
cat > bunfig.toml << 'CONFIG'
env = false
CONFIG
bun index.js
```
## Files Changed
- `src/cli/Arguments.zig` - CLI flag parsing
- `src/api/schema.zig` - API schema field with encode/decode
- `src/options.zig` - Env struct field and wiring
- `src/bunfig.zig` - Config parsing with loadEnvConfig
- `src/transpiler.zig` - Runtime wiring
- `src/bun.js.zig` - Runtime wiring
- `src/cli/exec_command.zig` - Runtime wiring
- `src/cli/run_command.zig` - Preserved package.json script runner
behavior
- `test/cli/run/no-envfile.test.ts` - Comprehensive test suite
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
### What does this PR do?
Three things:
- JSCommonJSExtensions.cpp `onAssign` was returning out of sync numbers
instead of `BunLoaderTypeJS`/`BunLoaderTypeNAPI`/...
- `bun.schema.api.Loader._none` was 255 instead of 254 like
`BunLoaderTypeNone`
- `Bun__transpileFile` used `bun.options.Loader.Optional` instead of
`bun.schema.api.Loader`. `bun.options.Loader` does not have a type kept
in sync in C++.
### How did you verify your code works?
Added tests that make sure the correct loader is used for modules
required with custom _extensions functions
## Summary
- Moved `jsxSideEffects` (now `sideEffects`) from tsconfig.json compiler
options to the jsx object in the build API
- Updated all jsx bundler tests to use the new jsx.sideEffects
configuration
- Added jsx configuration parsing to JSBundler.zig
## Changes
- Removed jsxSideEffects parsing from `src/resolver/tsconfig_json.zig`
- Added jsx configuration parsing to `src/bun.js/api/JSBundler.zig`
Config.fromJS
- Fixed TransformOptions to properly pass jsx config to the transpiler
in `src/bundler/bundle_v2.zig`
- Updated TypeScript definitions to include jsx field in BuildConfigBase
- Modified test framework to support jsx configuration in API mode
- Updated all jsx tests to use `sideEffects` in the jsx config instead
of `side_effects` in tsconfig
## Test plan
All 27 jsx bundler tests are passing with the new configuration
structure.
🤖 Generated with [Claude Code](https://claude.ai/code)
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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
tests not in `test/no-validate-leaksan.txt` will run with leaksanitizer
in CI
leaks documented in `test/leaksan.supp` will not cause a test failure
-- notes about leaksanitizer
- will not catch garbage collected objects accumulated during
long-running processes
- will not catch js objects (eg a strong held to a promise)
- will catch native calls to `malloc` not `free`d
- will catch allocations made in C, Zig, C++, libc, dependencies,
dlopen'd
---------
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
## Summary
- Removes unused function and class expression names when
`--minify-syntax` is enabled during bundling
- Adds `--keep-names` flag to preserve original names when minifying
- Matches esbuild's minification behavior
## Problem
When minifying with `--minify-syntax`, Bun was keeping function and
class expression names even when they were never referenced, resulting
in larger bundle sizes compared to esbuild.
**Before:**
```js
export var AB = function A() { };
// Bun output: var AB = function A() {};
// esbuild output: var AB = function() {};
```
## Solution
This PR adds logic to remove unused function and class expression names
during minification, matching esbuild's behavior. Names are only removed
when:
- `--minify-syntax` is enabled
- Bundling is enabled (not transform-only mode)
- The scope doesn't contain direct eval (which could reference the name
dynamically)
- The symbol's usage count is 0
Additionally, a `--keep-names` flag has been added to preserve original
names when desired (useful for debugging or runtime reflection).
## Testing
- Updated existing test in `bundler_minify.test.ts`
- All transpiler tests pass
- Manually verified output matches esbuild for various cases
## Examples
```bash
# Without --keep-names (names removed)
bun build --minify-syntax input.js
# var AB = function() {}
# With --keep-names (names preserved)
bun build --minify-syntax --keep-names input.js
# var AB = function A() {}
```
🤖 Generated with [Claude Code](https://claude.ai/code)
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
## Summary
Implements the `jsxSideEffects` option to control whether JSX elements
are marked as pure for dead code elimination, matching esbuild's
behavior from their TestJSXSideEffects test case.
## Features Added
- **tsconfig.json support**: `{"compilerOptions": {"jsxSideEffects":
true}}`
- **CLI flag support**: `--jsx-side-effects`
- **Dual runtime support**: Works with both classic
(`React.createElement`) and automatic (`jsx`/`jsxs`) JSX runtimes
- **Production/Development modes**: Works in both production and
development environments
- **Backward compatible**: Default value is `false` (maintains existing
behavior)
## Behavior
- **Default (`jsxSideEffects: false`)**: JSX elements marked with `/*
@__PURE__ */` comments (can be eliminated by bundlers)
- **When `jsxSideEffects: true`**: JSX elements NOT marked as pure
(always preserved)
## Example Usage
### tsconfig.json
```json
{
"compilerOptions": {
"jsxSideEffects": true
}
}
```
### CLI
```bash
bun build --jsx-side-effects
```
### Output Comparison
```javascript
// Input: console.log(<div>test</div>);
// Default (jsxSideEffects: false):
console.log(/* @__PURE__ */ React.createElement("div", null, "test"));
// With jsxSideEffects: true:
console.log(React.createElement("div", null, "test"));
```
## Implementation Details
- Added `side_effects: bool = false` field to `JSX.Pragma` struct
- Updated tsconfig.json parser to handle `jsxSideEffects` option
- Added CLI argument parsing for `--jsx-side-effects` flag
- Modified JSX element visiting logic to respect the `side_effects`
setting
- Updated API schema with proper encode/decode support
- Enhanced test framework to support the new JSX option
## Comprehensive Test Coverage (12 Tests)
### Core Functionality (4 tests)
- ✅ Classic JSX runtime with default behavior (includes `/* @__PURE__
*/`)
- ✅ Classic JSX runtime with `side_effects: true` (no `/* @__PURE__ */`)
- ✅ Automatic JSX runtime with default behavior (includes `/* @__PURE__
*/`)
- ✅ Automatic JSX runtime with `side_effects: true` (no `/* @__PURE__
*/`)
### Production Mode (4 tests)
- ✅ Classic JSX runtime in production with default behavior
- ✅ Classic JSX runtime in production with `side_effects: true`
- ✅ Automatic JSX runtime in production with default behavior
- ✅ Automatic JSX runtime in production with `side_effects: true`
### tsconfig.json Integration (4 tests)
- ✅ Default tsconfig.json behavior (automatic runtime, includes `/*
@__PURE__ */`)
- ✅ tsconfig.json with `jsxSideEffects: true` (automatic runtime, no `/*
@__PURE__ */`)
- ✅ tsconfig.json with `jsx: "react"` and `jsxSideEffects: true`
(classic runtime)
- ✅ tsconfig.json with `jsx: "react-jsx"` and `jsxSideEffects: true`
(automatic runtime)
### Snapshot Testing
All tests include inline snapshots demonstrating the exact output
differences, providing clear documentation of the expected behavior.
### Existing Compatibility
- ✅ All existing JSX tests continue to pass
- ✅ Cross-platform Zig compilation succeeds
## Closes
Fixes#22295🤖 Generated with [Claude Code](https://claude.ai/code)
---------
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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Replace `catch bun.outOfMemory()`, which can accidentally catch
non-OOM-related errors, with either `bun.handleOom` or a manual `catch
|err| switch (err)`.
(For internal tracking: fixes STAB-1070)
---------
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
### What does this PR do?
This PR adds builtin YAML parsing with `Bun.YAML.parse`
```js
import { YAML } from "bun";
const items = YAML.parse("- item1");
console.log(items); // [ "item1" ]
```
Also YAML imports work just like JSON and TOML imports
```js
import pkg from "./package.yaml"
console.log({ pkg }); // { pkg: { name: "pkg", version: "1.1.1" } }
```
### How did you verify your code works?
Added some tests for YAML imports and parsed values.
---------
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>
### What does this PR do?
The `then` function in `transpiler.transform` can cause GC, which means
it can cause the `Transpiler` to become freed, which means that if that
same transpiler is in use by another run on the other thread, it could
have pointers to invalid memory.
Also, `ESMCondition` has unnecesasry memory allocations and there is a
very tiny memory leak in optionsFromLoaders
### How did you verify your code works?
Existing tests
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
