robobun f88f60af5a fix(bundler): throw error when Bun.build is called from macro during bundling (#26361) ...

## Summary
- Fixes #26360
- Detects when `Bun.build` is called from within macro mode during
bundling and throws a clear error instead of hanging indefinitely

## Problem
When `Bun.build` API is called to bundle a file that imports from a
macro which itself uses `Bun.build`, the process would hang indefinitely
due to a deadlock:

1. The bundler uses a singleton thread for processing `Bun.build` calls
2. During parsing, when a macro is encountered, it's evaluated on that
thread
3. If the macro calls `Bun.build`, it tries to enqueue to the same
singleton thread
4. The singleton is blocked waiting for macro completion → deadlock

## Solution
Added a check in `Bun.build` that detects when it's called from macro
mode (`vm.macro_mode`) and throws a clear error with guidance:

```
Bun.build cannot be called from within a macro during bundling.

This would cause a deadlock because the bundler is waiting for the macro to complete,
but the macro's Bun.build call is waiting for the bundler.

To bundle code at compile time in a macro, use Bun.spawnSync to invoke the CLI:
  const result = Bun.spawnSync(["bun", "build", entrypoint, "--format=esm"]);
```

## Test plan
- [x] Added regression test in `test/regression/issue/26360.test.ts`
- [x] Verified test hangs/fails with system Bun (the bug exists)
- [x] Verified test passes with the fix applied
- [x] Verified regular `Bun.build` (not in macro context) still works

🤖 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: Jarred Sumner <jarred@jarredsumner.com>

2026-01-23 20:24:12 -08:00

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