Here's some backstory:
* on macOS, @cole-miller and I noticed that since roughly Oct 2025, due
to some changes to latest macOS Tahoe, for any spawned child process we
needed to reset Mach exception ports
(https://github.com/zed-industries/zed/issues/36754 +
https://github.com/RemiKalbe/zed/commit/6e8f2d2ebe5a93753625a3026aeb996de8cb436b)
* the changes in that PR achieve that via `pre_exec` hook on
`std::process::Command` which then abandons `posix_spawn` syscall for
`fork` + `execve` dance on macOS (we tracked it down in Rust's std
implementation)
* as it turns out, `fork` + `execve` is pretty expensive on macOS
(apparently way more so than on other OSes like Linux) and `fork` takes
a process-wide lock on the allocator which is bad
* however, since we wanna reset exception ports on the child, the only
official way supported by Rust's std is to use `pre_exec` hook
* posix_spawn on macOS exposes this tho via a macOS specific extension
to that syscall `posix_spawnattr_setexceptionports_np` but there is no
way to use that via any standard interfaces in `std::process::Command`
* thus, it seemed like a good idea to instead create our own custom
Command wrapper that on non-macOS hosts is a zero-cost wrapper of
`smol::process::Command`, while on macOS we reimplement the minimum to
achieve `smol::process::Command` with `posix_spawn` under-the-hood
Notably, this changeset improves git-blame in very large repos
significantly.
Release Notes:
- Fixed performance spawning child processes on macOS by always forcing
`posix_spawn` no matter what.
---------
Co-authored-by: Cole Miller <cole@zed.dev>
## Summary
Follow-up to #40716. This applies the same `reset_exception_ports()` fix
to `set_pre_exec_to_start_new_session()`, which is used by shell
environment capture, terminal spawning, and DAP transport.
### Root Cause
After more debugging, I finally figured out what was causing the issue
on my machine. Here's what was happening:
1. Zed spawns a login shell (zsh) to capture environment variables
2. A pipe is created: reader in Zed, writer mapped to fd 0 in zsh
3. zsh sources `.zshrc` → loads oh-my-zsh → runs poetry plugin
4. Poetry plugin runs `poetry completions zsh &|` in background
5. Poetry inherits fd 0 (the pipe's write end) from zsh
6. zsh finishes `zed --printenv` and exits
7. Poetry still holds fd 0 open
8. Zed's `reader.read_to_end()` blocks waiting for all writers to close
9. Poetry hangs (likely due to inherited crash handler exception ports
interfering with its normal operation)
10. Pipe stays open → Zed stuck → no more processes spawn (including
LSPs)
I confirmed this by killing the hanging `poetry` process, which
immediately unblocked Zed and allowed LSPs to start. However, this
workaround was needed every time I started Zed.
While poetry was the culprit in my case, this can affect any shell
configuration that spawns background processes during initialization
(oh-my-zsh plugins, direnv, asdf, nvm, etc.).
Fixes#36754
## Test plan
- [x] Build with `ZED_GENERATE_MINIDUMPS=true` to force crash handler
initialization
- [x] Verify crash handler logs appear ("spawning crash handler
process", "crash handler registered")
- [x] Confirm LSPs start correctly with shell plugins that spawn
background processes
Release Notes:
- Fixed an issue on macOS where LSPs could fail to start when shell
plugins spawn background processes during environment capture.
## Summary
Fixes#36754
This PR fixes an issue where LSPs fail to spawn after the crash handler
is initialized.
## Problem
After PR #35263 added minidump crash reporting, some users experienced
LSP spawn failures. The issue manifests as:
- LSPs fail to spawn with no clear error messages
- The problem only occurs after crash handler initialization
- LSPs work when a debugger is attached, revealing a timing issue
### Root Cause
The crash handler installs Mach exception ports for minidump generation.
Due to a timing issue, child processes inherit these exception ports
before they're fully stabilized, which can block child process spawning.
## Solution
Reset exception ports in child processes using the `pre_exec()` hook,
which runs after `fork()` but before `exec()`. This prevents children
from inheriting the parent's crash handler exception ports.
### Implementation
- Adds macOS-specific implementation of `new_smol_command()` that resets
exception ports before exec
- Calls `task_set_exception_ports` to reset all exception ports to
`MACH_PORT_NULL`
- Graceful error handling: logs warnings but doesn't fail process
spawning if port reset fails
Release Notes:
- Fixed LSPs failing to spawn on some macOS systems
---------
Co-authored-by: Julia Ryan <juliaryan3.14@gmail.com>
