When restarting Zed, I hit a bug where all Git operations were hung. I
realized that there was a hanging git process running `git cat-file
--batch-check=%(objectname)`. The process was waiting on stdin. This was
surprising, because [the
code](https://github.com/zed-industries/zed/blob/e2bbdb19b6da2ee157ca1d36100acde2134a1663/crates/git/src/repository.rs#L1665-L1709)
that spawns this process explicitly closes the pipe that is attached to
the process's stdin after writing a list of ref names.
Using Claude, I found that this could be caused by that pipe file
descriptor being cloned due to file descriptor inheritance when another
child process is `exec`'d while that stdin pipe is open. The fix is to
enhance our Darwin process spawning layer to set the close-on-exec flag
for the pipe file descriptors, so that they are not inherited by child
processes spawned using code paths that don't set
`POSIX_SPAWN_CLOEXEC_DEFAULT`.
Release Notes:
- Fixed a bug on macOS where Git operations could be blocked depending
on the timing of spawning child processes.
## Context
Closes#11473
In-house Zed implementation of devcontainers. Replaces the dependency on
the [reference implementation](https://github.com/devcontainers/cli) via
Node.
This enables additional features with this implementation:
1. Zed extensions can be specified in the `customizations` block, via
this syntax in `devcontainer.json:
```
...
"customizations": {
"zed": {
"extensions": ["vue", "ruby"],
},
},
```
2.
[forwardPorts](https://containers.dev/implementors/json_reference/#general-properties)
are supported for multiple ports proxied to the host
## How to Review
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## Self-Review Checklist
<!-- Check before requesting review: -->
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable
Release Notes:
- Improved devcontainer implementation by moving initialization and
creation in-house
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>
Max Brunsfeld