Saving after undo may unexpectedly modify code (lines removed or duplicated)

[Fringale]

First off, thank you for the EmmyLua extension and language server!

On my system (Zed 0.225.13 Flatpak on Linux), saving a Lua file can sometimes unexpectedly alter the code after an undo operation. In some cases, lines may be removed, duplicated, or previously deleted code may reappear.

Below is a minimal example where the issue is reproducible.

Tested with default Zed and EmmyLua configuration:

• only HTML and EmmyLua extensions installed in Zed
• empty settings.json in Zed
• no .emmyrc.json, .luarc.json, editor.config or EmmyLua-specific settings

Also tested with today's Zed 0.226.4 version.

---

Steps to reproduce

1. Type the following Lua code in a new file

if true then
	print(1)
end

print(2)

2. Save as a .lua file and ensure that the EmmyLua language server is running

3. Select and delete the if block

4. Save the file: the EmmyLuaCodeStyle formatter removes the leading empty lines

5. Press Undo twice, to first restore the empty lines then the if block

6. Save the file again

Expected behaviour

Saving should not modify the code, as there is nothing left to format.

Actual behavior

The if statement is removed after saving.

---

With additional edits, saves, and undo operations, the print(2) line ended up being duplicated and a previously deleted if block reappeared, however I could not yet found a reliable way to reproduce those cases consistently.

I suspect that this might be related to EmmyLuaCodeStyle, but I was unable to reproduce similar issues when using the LuaLS extension with the integrated EmmyLuaCodeStyle enabled.

[CppCXY]

From the symptoms, it appears the undo operation in Zed isn't being synced to the language server (LS) in time, and emmylua's save action doesn't update the file contents, so the language server's copy isn't the current/latest file. I need to investigate this tomorrow and check whether multiple editors behave the same way; I reasonably suspect this is caused by Zed itself.

[Fringale]

Thanks, it seems like a syncing issue indeed as I sometimes get in this kind of state where EmmyLuaLS does not seem to have the latest information:

The if block was deleted, but the diagnostic for the if line and the highlight for the end keyword are still displayed.

[CppCXY]

I verified in both VSCode and IntelliJ that after an undo operation, they sync the latest content to the LS. This is very likely an issue with Zed itself.

[Fringale]

Hey! Just checking in on this, have you had a chance to investigate further?

Let me know if you'd like me to try specific debugging steps or capture specific logs (LSP logs, RPC traces, a minimal repro project, etc.), especially if you're unable to reproduce the issue on your side.

One additional observation: adding delays between the steps (delete → save → undo → save) does not seem to change the behavior. I can still reproduce the issue consistently even when waiting a few seconds between each action.

[CppCXY]

After a few quick attempts, I can no longer reproduce the issue.

[Fringale]

Thanks for the screen recording! I’m not sure what could explain the difference in behavior, as I’m consistently able to reproduce the issue on my side (Linux, Zed 0.227.1 Flatpak using default configuration + EmmyLua extension with default configuration).

Here is the equivalent of your recording, showcasing the issue after starting Zed on my system:

Case1.mp4

I could also capture the case where a previously deleted block reappears after saving, it seems to happen reliably when opening a file with the full example already present:

Case2.mp4

Don't hesitate to tell me if there’s anything specific you’d like me to test or capture.

[CppCXY]

@0x2CA any advice?

[0x2CA]

@0x2CA any advice?

I have no way of reproducing the problem, I have tried several times to use mouse menu actions, or vim actions, and none of them have reproduced the problem

Zed: v0.228.0+preview.201.7d41a5350a09e4e0ef25194b99e5a3f279bcc230 (Zed Preview) 
OS: macOS 26.3.1
Memory: 32 GiB
Architecture: aarch64

[0x2CA]

@Fringale EmmyLuaCodeStyle？

buffer: Reload after undo when file changed while dirty #51037

[CppCXY]

@Fringale Can you upgrade to 0.228 version?

[Fringale]

Thanks both for taking the time to investigate this!

I upgraded to Zed 0.228 as suggested, and indeed zed-industries/zed#51037 did seem like a very plausible cause (nice catch). In addition, to rule out any Flatpak weirdness I tested this time with the .tar.gz install package.

But unfortunately even with these changes I’m still seeing the same behavior on my side. Here’s a screen recording with this 0.228 .tar.gz install (fresh Zed install with default conf and EmmyLua extension):

0.228.mp4

Regarding EmmyLuaCodeStyle: for all the tests in this thread I did not change the default settings of the EmmyLua extension, so the integrated EmmyLuaCodeStyle formatter is active with its default settings.

Happy to help dig further into this.

Zed: 0.228.0+stable.203.8421009ef8a022df1196d54bb42fd94366ec0988
OS: Linux (Aeon Desktop: openSUSE Tumbleweed immutable derivative)
Desktop environment: GNOME 49.4

[Fringale]

To rule out environment-specific issues, I tested on fresh Fedora 43 live ISOs (both Workstation GNOME and KDE Plasma Desktop), using the Zed 0.228.0 .tar.gz manual download with only the EmmyLua extension installed.

=> I was able to reproduce that same problematic undo→save behavior in both environments, suggesting the issue is not specific to my system but exists in at least several Linux distros.

If it helps with reproduction, you could try running Fedora Workstation 43 in a VM and testing with a clean Zed install + EmmyLua extension.

[CppCXY]

I plan rewrite a formatter, This is definitely a behavior of the Zed editor itself that isn't working as expected; we don't have enough devices to verify it, so let's wait until the new formatter is released.

[Fringale]

Thanks for the update, I’ll keep an eye on the progress of the new formatter and the Zed extension then!

Don't hesitate to let me know if there’s anything I can test on Linux to help validate changes in the meantime.