Home directory on alternate volume causes "Failed to write settings to file"

[notpeter]

Summary

User home directories on volumes other than / prevent Zed from performing actions which modify ~/.config/zed/settings.json.

Steps to trigger the problem:

1. Create a new APFS volume or attach an external drive.
2. Create a new user whose home directory on a drive other than /
3. Open Zed, do some action which attempts to re-write settings (select model from Assistant, change default keymap, etc).

Actual Behavior:

2024-09-12T08:19:33.679273+10:00 [ERROR] Failed to write settings to file "/Users/ext/xxx/.config/zed/settings.json"

Caused by:
0: failed to persist temporary file: Cross-device link (os error 18)
1: Cross-device link (os error 18)

Expected Behavior:
Settings file is saved.

Workaround:
Create a symlink at `~/

Editors note (@notpeter): I have not performed these steps and derived them from comments here:

• Unable to select Claude 3.5 Sonnet Zed model #16618 (comment)

Zed Version and System Specs

Zed: v0.150.0 (Zed Preview)
OS: macOS 15.0.0
Memory: 16 GiB
Architecture: x86_64

[kopparam]

Yep this is my setup and I can reproduce this error and workaround.

[kopparam]

@notpeter my thoughts on this if it helps.

Searching for the error reveals that it is from Rust and happens when it tries to write to a file which hard links to the source file on another file system. Is the setting.json stored in /tmp or something?

[notpeter]

Doesn't require hard links, just moving/renaming across file system boundaries.

I haven't looked at this code specifically, but likely Zed is likely writing the new content to a file and then renaming it into place. The thinking is that this makes the update more-atomic and there is little chance of a half-written settings file on disk.

I think we should be potentially able to stat the ~/.config/zed/settings.json (or the target file if it is a symlink) and the temporary dir to compare if they are on on the same filesystem and if so, use the existing code, and if not write the file in an alternate way.

stat -f=%d "$(readlink -f ~/.config/zed/settings.json)"
stat -f=%d /tmp