Regression: Diagnostic message getting overwritten by an empty RPC message

[kartikvashistha]

Summary

Hi team, hope you are all doing well!

I have just discovered a regression in the current main build of Zed, where a diagnostic message sent from an LSP is incorrectly getting overwritten by an empty recieved RPC message. This prevents it from appearing under the diagnostics pane (it actually does appear there momentarily, but disappears immediately after this empty diagnostic message is sent).

Preview of this under LSP logs is as follows:

// Receive:
{"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"uri":"file:///Users/kartik/code/personal/zed-ansible//example/roles/setup-fedora/handlers/main.yml","diagnostics":[{"message":"Too many blank lines (3 > 2)","range":{"start":{"line":10,"character":0},"end":{"line":10,"character":2147483647}},"severity":1,"source":"ansible-lint","code":"yaml[empty-lines]","codeDescription":{"href":"https://ansible.readthedocs.io/projects/lint/rules/yaml/"}},{"message":"All names should start with an uppercase letter.","range":{"start":{"line":11,"character":0},"end":{"line":11,"character":2147483647}},"severity":1,"source":"ansible-lint","code":"name[casing]","codeDescription":{"href":"https://ansible.readthedocs.io/projects/lint/rules/name/"}}]}}
// Receive:
{"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"uri":"file:///Users/kartik/code/personal/zed-ansible/example/roles/setup-fedora/handlers/main.yml","diagnostics":[]}}

This issue is not observed under the current stable release:

Zed: v0.174.6 (Zed) 
OS: macOS 15.3.1
Memory: 32 GiB
Architecture: aarch64

Steps to trigger the problem:

1. Clone this repo;
2. Install the Ansbile extension;
3. Setup the extension per the readme;
4. Open this file and observe RPC Messages under ansible-language-server logs.

Actual Behavior:
No diagnostic message appears (or more accurately: appears very briefly before being cleared up).

Expected Behavior:
The file should fail linting as all tasks name should be in uppercase, and as such a relevant diagnostic message should appear under the diagnostics pane.

Zed Version and System Specs

Zed: v0.176.0 (Zed Dev 328e4d6)
OS: macOS 15.3.1
Memory: 32 GiB
Architecture: aarch64

[kartikvashistha]

Update: I have found the PR that introduces this regression (commit sha: a618830aead84ebc50cb14141032faf83f5ef294). CC: @osiewicz

[osiewicz]

Hey @kartikvashistha ! Thanks for digging in and bisecting. I have a fix ready, but honestly it's quite weird - I'm pretty sure it's an issue upstream.

Story time (if you're interested)

The empty message you're seeing is sent by language server - we don't really produce them (well, not the `publishDiagnostics` ones). This means that the language server is sending us two `publishDiagnostics` notifications, one after the other. But why does it do that and why does the PR you've linked matter? #24038 flipped our handling of language servers on it's head. I went ahead and captured a messy diff of communication with language servers with latest Nightly (where the issue is reproducible) and with 0.174.6. https://www.diffchecker.com/C06DBNky/

The comms are the same, we exchange the same messages.. everything seems in tact.
Another thing that may have an effect on behavior of language server is the initialize request we send out; it describes Zed's capabilities as a client. It's also the first message we sent in the log shared above.
It did not change though! We still fill out the same fields (even though #24038 definitely could have changed that part) so everything should be okay.
Wait. Hold on.
In workspace_folders (which points at source code locations, basically) we've added a trailing slash to the path to your project.

This can't be it, right?... No, that's it! When we pass in workspace folder with a trailing slash (which is valid btw, as it's a path to a directory), ansible LS starts sending out bogus publishDiagnostics notifications.

Thanks for the report. The fix should be out on Preview on 5th March and on Stable on 12th March.

[kartikvashistha]

Thank you so much for the detailed explanation and speedy fix @osiewicz - I really enjoyed reading that!

[osiewicz]

The fix is now on Preview

[kartikvashistha]

Thank you @osiewicz , I can confirm all's well now in the latest Preview build:

Zed: v0.177.0 (Zed Preview) 
OS: macOS 15.3.1
Memory: 32 GiB
Architecture: x86_64