Stale Diagnostics

[jarednorman]

I'm not clear if this is an issue with the LSP or the Zed integration, but in Zed I'm getting stale results using ReScript 12, latest release of the LSP, and latest Zed. I've provide a couple of screenshots and some explanation here. Not sure how to proceed in validating which project is actually causing this.

I hadn't worked on any ReScript in a little while. I did validate the issue on a ReScript 11 project too.

[jarednorman]

I’ve just confirmed that it works fine in VSCode, so leaning towards this being a Zed integration issue.

[KidkArolis]

Yeah, I can see this issue too 😭 with the latest version on main if you set up a local version with make build..

The rescript watcher rebuilds, but the extension / LSP is not seeing this at all..

Hmmmm

[KidkArolis]

# tail -f ~/Library/Logs/Zed/Zed.log

2025-12-17T11:46:58+00:00 INFO  [lsp] starting language server process. binary path: "/Users/karolis/.asdf/shims/node", working directory: "/Users/karolis/humaans/humaans", args: ["/Users/karolis/Library/Application Support/Zed/extensions/work/rescript/node_modules/.bin/rescript-language-server", "--stdio"]
2025-12-17T11:46:58+00:00 INFO  [lsp] Language server with id 11 sent unhandled notification rescript/compilationStatus:
{
  "project": "client",
  "projectRootPath": "/Users/karolis/humaans/humaans/app/client",
  "status": "error",
  "errorCount": 2,
  "warningCount": 0
}

[KidkArolis]

OK, looks like this broke since @rescript/language-server@1.64.0 removed file watching and require the editor to support workspace_didChangeWatchedFiles, which I'm not sure yet how to integrate into Zed or whether that's possible with the current extension API.

In the meantime, the workaround is to revert to the older language server by adding this into your Zed settings (cmd + ,):

"lsp": {
    "rescript-language-server": {
      "settings": {
        "version": "1.62.0",
      },
    },
  }

Note: this lsp configuration is only available in rescript-zed@0.4.1 which is still pending a merge from Zed zed-industries/extensions#4161.

[KidkArolis]

A bit more context from Opus:

After initialization, the ReScript LSP sends a client/registerCapability request asking the editor to watch these patterns:

• {projectRoot}/**/lib/bs/.compiler.log - triggers diagnostic updates
• {projectRoot}/**/lib/bs/build.ninja - triggers project config cache sync
• {projectRoot}/**/lib/bs/**/*.{cmt,cmi} - for incremental compilation

When compiler.log changes (after each compilation), the editor should send a workspace/didChangeWatchedFiles notification, which triggers the LSP to read the new diagnostics and push them to the editor.

Why it doesn't work with Zed: While Zed implements LSP file watching, there are potential issues with:

• Gitignored directories: The lib/bs directory is typically in .gitignore, and Zed's file watching is tied to its worktree system which may not track ignored directories
• Hidden files: The .compiler.log file starts with a dot, which may be filtered out
• Glob pattern matching: The patterns sent by ReScript use absolute paths which may not match Zed's expected format

[nojaf]

I believe the problem might be related to b3ce82b.
There extensionConfiguration is passed and that is completely overriding the incrementalTypechecking node, thus making that false.

If that is the problem, rescript-lang/rescript-vscode#1162 would fix that.

You could also try adding:

  "lsp": {
    "rescript-language-server": {
      "initialization_options": {
        "extensionConfiguration": {
          "incrementalTypechecking":{
			"enable": "true"
		  }
        }
      },
    }
  },

[KidkArolis]

Yes, I think setting incrementalTypechecking.enabled to true works.

[nojaf]

Maybe 1.72.0 fixes the problem.

[jarednorman]

Maybe 1.72.0 fixes the problem.

I just upgraded to this version and it didn't change anything.

[jarednorman]

Okay, added the "incrementalTypechecking" option and now using 1.72.0 seems to have got it working. My project settings file for anyone interested:

{
  "lsp": {
    "rescript-language-server": {
      "binary": {
        "path": "./node_modules/.bin/rescript-language-server",
        "arguments": ["--stdio"],
      },
      "initialization_options": {
        "extensionConfiguration": {
          "askToStartBuild": false,
          "incrementalTypechecking": {
            "enable": "true",
          },
        },
      },
    },
  },
}

Worth noting that I installed the language server into the project and specified the path to get the correct version.

[KidkArolis]

Are you running 0.3.0 (can check in Zed > Extensions) or from source via make build?

I didn't think 0.3.0 accepted settings, but maybe it did 🤔

Shouldn't need the "incrementalTypechecking": { "enable": "true", }. It's a bit difficult to know which version of LSP you're running any given time. It took me a bit of fiddling too, could you try:

1. comment out all of that lsp config
2. restart zed
3. open some rescript file
4. run cmd shift p "restart language server"
5. notice if it says "downloading language server" bottom left

It should just work then 🤷‍♂️

[jarednorman]

Okay, I commented out the config and restarted Zed. Noticed it said something like "updating ReScript extension" or something like that in the status bar. Everything was working, warnings/errors showing as expected. Checked the extension version and it showed v0.4.1.

Then I restarted the language server. Did not see it say "downloading language server". Now we're back to where we started, warnings/errors not updating. Confirmed that the version of the LSP that's running (located at $HOME/Library/Application Support/Zed/extensions/work/rescript/node_modules/@rescript/language-server/out/cli.js) is v1.72.0, though.

[nojaf]

@jarednorman just want to double-check but are you using rescript-legacy to build?
Do you have files like lib/rescript.lock, lib/bs/compiler-info.json and lib/bs/.compiler.log?
What do those say?

[jarednorman]

lib/rescript.lock:

16179

lib/bs/compiler-info.json:

{
  "version": "12.0.1",
  "bsc_path": "/Users/jardo/Codes/wizard-manager/node_modules/@rescript/darwin-arm64/bin/bsc.exe",
  "bsc_hash": "0f6c65d7a86d5e5e53b36a4ea449419e755c475b510f7e3f60d714b64cca0499",
  "rescript_config_hash": "6061e0e92ca66a811179c9ab0b3abdee017bd01c367b153e9cc0cc8f5c793276",
  "runtime_path": "/Users/jardo/Codes/wizard-manager/node_modules/@rescript/runtime",
  "generated_at": "1766019252865"
}

lib/bs/.compiler.log:

#Start(1766019252822)
#Done(1766019252864)

[jarednorman]

Okay, so here's something upsetting but perhaps helpful: I just rebooted Zed a bunch of times and sometimes I experienced the issue and sometimes I didn't. Race condition or something maybe?

This is all I have in my config rn:

{
  "lsp": {
    "rescript-language-server": {
      "initialization_options": {
        "extensionConfiguration": {
          "askToStartBuild": false,
        },
      },
    },
  },
}