## 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
🤖 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>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
## Summary
Implements the `typeof undefined === 'u'` minification optimization from
esbuild in Bun's minifier, and fixes dead code elimination (DCE) for
typeof comparisons with string literals.
### Part 1: Minification Optimization
This optimization transforms:
- `typeof x === "undefined"` → `typeof x > "u"`
- `typeof x !== "undefined"` → `typeof x < "u"`
- `typeof x == "undefined"` → `typeof x > "u"`
- `typeof x != "undefined"` → `typeof x < "u"`
Also handles flipped operands (`"undefined" === typeof x`).
### Part 2: DCE Fix for Typeof Comparisons
Fixed dead code elimination to properly handle typeof comparisons with
strings (e.g., `typeof x <= 'u'`). These patterns can now be correctly
eliminated when they reference unbound identifiers that would throw
ReferenceErrors.
## Before/After
### Minification
Before:
```javascript
console.log(typeof x === "undefined");
```
After:
```javascript
console.log(typeof x > "u");
```
### Dead Code Elimination
Before (incorrectly kept):
```javascript
var REMOVE_1 = typeof x <= 'u' ? x : null;
```
After (correctly eliminated):
```javascript
// removed
```
## Implementation
### Minification
- Added `tryOptimizeTypeofUndefined` function in
`src/ast/visitBinaryExpression.zig`
- Handles all 4 equality operators and both operand orders
- Only optimizes when both sides match the expected pattern (typeof
expression + "undefined" string)
- Replaces "undefined" with "u" and changes operators to `>` (for
equality) or `<` (for inequality)
### DCE Improvements
- Extended `isSideEffectFreeUnboundIdentifierRef` in `src/ast/P.zig` to
handle comparison operators (`<`, `>`, `<=`, `>=`)
- Added comparison operators to `simplifyUnusedExpr` in
`src/ast/SideEffects.zig`
- Now correctly identifies when typeof comparisons guard against
undefined references
## Test Plan
✅ Added comprehensive test in `test/bundler/bundler_minify.test.ts` that
verifies:
- All 8 variations work correctly (4 operators × 2 operand orders)
- Cases that shouldn't be optimized are left unchanged
- Matches esbuild's behavior exactly using inline snapshots
✅ DCE test `dce/DCETypeOfCompareStringGuardCondition` now passes:
- Correctly eliminates dead code with typeof comparison patterns
- Maintains compatibility with esbuild's DCE behavior
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
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>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
### What does this PR do?
Reduce stack space usage of parseSuffix
### How did you verify your code works?
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Splits up js_parser.zig into multiple files. Also changes visitExprInOut
to use function calls rather than switch
Not ready:
- [ ] P.zig is ~70,000 tokens, still needs to get smaller
- [x] ~~measure zig build time before & after (is it slower?)~~ no
significant impact
---------
Co-authored-by: pfgithub <6010774+pfgithub@users.noreply.github.com>
