robobun 6386eef8aa fix(bunx): handle empty string arguments on Windows (#25025) ...

## Summary

Fixes #13316
Fixes #18275

Running `bunx cowsay ""` (or any package with an empty string argument)
on Windows caused a panic. Additionally, `bunx concurrently "command
with spaces"` was splitting quoted arguments incorrectly.

**Repro #13316:**
```bash
bunx cowsay ""
# panic(main thread): reached unreachable code
```

**Repro #18275:**
```bash
bunx concurrently "bun --version" "bun --version"
# Only runs once, arguments split incorrectly
# Expected: ["bun --version", "bun --version"]
# Actual: ["bun", "--version", "bun", "--version"]
```

## Root Cause

The bunx fast path on Windows bypasses libuv and calls `CreateProcessW`
directly to save 5-12ms. The command line building logic had two issues:

1. **Empty strings**: Not quoted at all, resulting in invalid command
line
2. **Arguments with spaces**: Not quoted, causing them to be split into
multiple arguments

## Solution

Implement Windows command-line argument quoting using libuv's proven
algorithm:
- Port of libuv's `quote_cmd_arg` function (process backwards + reverse)
- Empty strings become `""`
- Strings with spaces/tabs/quotes are wrapped in quotes
- Backslashes before quotes are properly escaped per Windows rules

**Why not use libuv directly?**
- Normal `Bun.spawn()` uses `uv_spawn()` which handles quoting
internally
- bunx fast path bypasses libuv to save 5-12ms (calls `CreateProcessW`
directly)
- libuv's `quote_cmd_arg` is a static function (not exported)
- Solution: port the algorithm to Zig

## Test Plan

- [x] Added regression test for empty strings (#13316)
- [x] Added regression test for arguments with spaces (#18275)
- [x] Verified system bun (v1.3.3) fails both tests
- [x] Verified fix passes both tests
- [x] Implementation based on battle-tested libuv algorithm

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

---------

Co-authored-by: Claude <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>

2025-12-15 17:29:04 -08:00

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