dart language-server --client-id emacs.eglot-dart times out *sometimes*

[dventimiglia]

Hello,

Sometimes, when I open a Dart file, the language server started by Eglot with dart language-server --client-id emacs.eglot-dart seems to fail with timed-out request errors. That is, the Eglot events buffer shows

[jsonrpc] i[13:23:34.826] [2] timed-out request ':textDocument/inlayHint'
[jsonrpc] i[13:23:38.966] [3] timed-out request ':textDocument/hover'
[jsonrpc] i[13:23:38.978] [4] timed-out request ':textDocument/documentHighlight'
[jsonrpc] i[13:23:38.978] [5] timed-out request ':textDocument/signatureHelp'

Restarting Eglot typically fixes it, though I then have to close the buffer and re-open the Dart file. I recognize that this might be an issue with the Dart language server and I'm willing to debug the issue, but I don't even know where to begin. Does anyone have any ideas? Thanks!

Best,
David

[manuel-uberti]

In order to understand whether it is indeed a problem with the language server, please try to follow these steps.

[dventimiglia]

Yeah, I dunno. The Dart language server has command line switches to log protocol and analyzer output, but when I try them with Eglot, it fails to get a connection altogether. Maybe that has something to do with Eglot creating the sub-process with a pipe instead of a pty, but that's totally a guess on my part.

Dart usage screen:

Start Dart's analysis server.

This is a long-running process used to provide language services to IDEs and other tooling clients.

It communicates over stdin and stdout and provides services like code completion, errors and warnings, and refactorings. This command is generally not user-facing but consumed by higher level tools.

For more information about the server's capabilities and configuration, see:

  https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server

Usage: dart language-server [arguments]
    --client-id=<name>                    An identifier for the analysis server client.
    --client-version=<version>            The version of the analysis server client.
    --dart-sdk=<path>                     Override the Dart SDK to use for analysis.
    --cache=<path>                        Override the location of the analysis server's cache.
    --packages=<path>                     The path to the package resolution configuration file, which supplies a mapping of package names
                                          into paths.
    --protocol=<protocol>                 Specify the protocol to use to communicate with the analysis server.

          [analyzer]                      Dart's analysis server protocol (https://dart.dev/go/analysis-server-protocol)
          [lsp] (default)                 The Language Server Protocol (https://microsoft.github.io/language-server-protocol)

Server diagnostics:
    --protocol-traffic-log=<file path>    Write server protocol traffic to the given file.
    --analysis-driver-log=<file path>     Write analysis driver diagnostic data to the given file.
    --diagnostic-port=<port>              Serve a web UI for status and performance data on the given port.
-h, --help                                Print this usage information.

Run "dart help" to see global options.

I tried setting that switch with this in init.el but no dice.

(with-eval-after-load 'eglot
  (add-to-list 'eglot-server-programs
	       '(dart-mode . (
			      "dart" "language-server"
			      "--client-id" "emacs.eglot-dart"
			      "--protocol-traffic-log=/dev/stderr"
			      ))))

Oh well. I'll keep futzing with it. Thanks for your help.

[joaotavora]

, it fails to get a connection altogether.

Eglot events buffer log for that?

Anyway, you may try to just manually send some JSON messages via stdin. Or you may try to obtain a transcript of some other client's successful LSP communication with that very server.

[dventimiglia]

Eglot events buffer log for that?

It just sorta times out after ~30 seconds, I guess. Screen-cast here: https://asciinema.org/a/6nauSHib0aFT7ybbix0gpmBxU

Eglot events buffer:

[jsonrpc] D[13:01:24.237] Running language server: dart language-server --client-id emacs.eglot-dart --protocol-traffic-log=/dev/stderr
[jsonrpc] e[13:01:24.238] --> initialize[1] {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"processId":204355,"clientInfo":{"name":"Eglot","version":"1.17"},"rootPath":"/home/davidaventimiglia/Scratch/eglot-problem-description/","rootUri":"file:///home/davidaventimiglia/Scratch/eglot-problem-description","initializationOptions":{},"capabilities":{"workspace":{"applyEdit":true,"executeCommand":{"dynamicRegistration":false},"workspaceEdit":{"documentChanges":true},"didChangeWatchedFiles":{"dynamicRegistration":true},"symbol":{"dynamicRegistration":false},"configuration":true,"workspaceFolders":true},"textDocument":{"synchronization":{"dynamicRegistration":false,"willSave":true,"willSaveWaitUntil":true,"didSave":true},"completion":{"dynamicRegistration":false,"completionItem":{"snippetSupport":true,"deprecatedSupport":true,"resolveSupport":{"properties":["documentation","details","additionalTextEdits"]},"tagSupport":{"valueSet":[1]}},"contextSupport":true},"hover":{"dynamicRegistration":false,"contentFormat":["markdown","plaintext"]},"signatureHelp":{"dynamicRegistration":false,"signatureInformation":{"parameterInformation":{"labelOffsetSupport":true},"documentationFormat":["markdown","plaintext"],"activeParameterSupport":true}},"references":{"dynamicRegistration":false},"definition":{"dynamicRegistration":false,"linkSupport":true},"declaration":{"dynamicRegistration":false,"linkSupport":true},"implementation":{"dynamicRegistration":false,"linkSupport":true},"typeDefinition":{"dynamicRegistration":false,"linkSupport":true},"documentSymbol":{"dynamicRegistration":false,"hierarchicalDocumentSymbolSupport":true,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]}},"documentHighlight":{"dynamicRegistration":false},"codeAction":{"dynamicRegistration":false,"resolveSupport":{"properties":["edit","command"]},"dataSupport":true,"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}},"isPreferredSupport":true},"formatting":{"dynamicRegistration":false},"rangeFormatting":{"dynamicRegistration":false},"rename":{"dynamicRegistration":false},"inlayHint":{"dynamicRegistration":false},"publishDiagnostics":{"relatedInformation":false,"codeDescriptionSupport":false,"tagSupport":{"valueSet":[1,2]}}},"window":{"showDocument":{"support":true},"workDoneProgress":true},"general":{"positionEncodings":["utf-32","utf-8","utf-16"]},"experimental":{}},"workspaceFolders":[{"uri":"file:///home/davidaventimiglia/Scratch/eglot-problem-description","name":"~/Scratch/eglot-problem-description/"}]}}
[stderr]  nil
[stderr]  1719950484309:Ver:1715358304115368422487:emacs.eglot-dart:unknown:1.37.0:3.4.0
[stderr]  nil
[stderr]  1719950484329:Noti:{"event"::"server.connected","params"::{"version"::"1.37.0","pid"::204421}}
[stderr]  1719950484331:Req:Content-Length:: 2633
[stderr]  1719950484332:Res:{"id"::"","error"::{"code"::"INVALID_REQUEST","message"::"Invalid request"}}
[stderr]  1719950484332:Req:
[stderr]  1719950484332:Res:{"id"::"","error"::{"code"::"INVALID_REQUEST","message"::"Invalid request"}}
[jsonrpc] i[13:01:54.248] [1] timed-out request ':initialize'
[jsonrpc] D[13:01:54.248] Connection state change: `killed
'

----------b---y---e---b---y---e----------
[stderr]  
[stderr]  
[stderr]  nil
[stderr]  nil
[stderr]  Process EGLOT (eglot-problem-description/(dart-mode)) stderr finished

Anyway, you may try to just manually send some JSON messages via stdin

I don't really know how to do that, but I'll try to figure it out.

Or you may try to obtain a transcript of some other client's successful LSP communication with that very server.

I tried figuring out if the VSCode Dart extension is using this language server, but I haven't quite figured that out. I'll take another run at it. Thanks!

[dventimiglia]

I guess I could try it with LSP mode, though I'm not a fan of that.

[joaotavora]

So VSCode doesn't speak LSP the server? Well, LSP is what Eglot speaks so ¯_(ツ)_/¯

[dventimiglia]

So VSCode doesn't speak LSP the server?

No, I'm quite sure that the VSCode Dart extension does speak LSP with the language server. What I didn't know then but do now is which language server does it speak to. Does it use /usr/bin/dart language-server or does it use something else, perhaps something built-in? Evidently, it does use /usr/bin/dart language-server. I added a log of its output to that repo here.

Well, LSP is what Eglot speaks

That was my understanding, yes.

[joaotavora]

Evidently, it does use /usr/bin/dart language-server.

Good, but not always so evident. Sometimes is does use a bundled version hidden somewhere, so you did well to doubt.

I added a log of its output to that repo here.

I can't see the initialize request there to compare it to Eglot's

[dventimiglia]

I can't see the initialize request there to compare it to Eglot's

They don't make it easy, now do they? From ps evidently this is how VSCode launches the language server process. It's pretty much the same. I did manage to add the command-line switches to capture the protocol communication.

/usr/lib/dart/bin/dart language-server --protocol=lsp --client-id=VS-Code --client-version=3.92.0 --protocol-traffic-log=protocol.log --analysis-driver-log=analysis.log

The captured communication is in protocol.log in the repo. There's a diff of the initialization between Eglot and VSCode. VSCode does some more experimental stuff, but beyond that I don't see anything dramatically different.

I also tried increasing jsonrpc-default-request-timeout from 10s to 30s. All that did was cause the "timed-out request" messages to take longer to appear.

OK, time to try out LSP Mode. ¯_(ツ)_/¯