CPU usage with vscode and the petrol library

[clecat]

Hello,

I am currently working with the library petrol while coding in vscode and I have encountered a strange issue with ocamllsp: Indeed, whenever I try to code SQL queries using Petrol's Query and Expr modules, my whole editor seems to slow down quite substantially and code correction stops working altogether.

When I check my processes, it appears that the ocamllsp process has a CPU usage of 100%. The only "workaround" is found is to kill the process and use the short time window where everything works fine before it starts again.

I figured I should open this issue as you might have better solutions,
Thank you for your time, Gwen

[voodoos]

Thanks to Gwen's guidance I was able to reproduce the issue consistently. It is to the codeActions request that enters a seamingly infinite loop.

There is workaround in vscode: disable the display of the code action lightbulb 💡

[qexat]

I stumbled upon an issue that seems to be of the same origin, so I crafted a minimal piece of code that triggers the bug:

type 'item list =
  | []
  | ( :: ) of ('item * 'item list)

module List = struct
  type 'item t = 'item list

  (* start typing some new definition here, for example reverse_concat *)
end

Specs

EndeavourOS Linux 6.14.10-arch1-1
OCaml v5.3.0
ocamllsp v1.22.0
Visual Studio Code v1.100.3 (258e40fedc6cb8edf399a463ce3a9d32e7e1f6f3)

[voodoos]

Thanks a lot @qexat, this is a surprisingly minimal example !

So far I have not been able to reproduce, I must be missing some context. Could you share the dune file and other relevant configuration information ? Or better, an archive with a minimum project ?

[qexat]

Huh, weird, my folder repro is literally just a file Repro.ml containing the code I have sent

Have you started typing a new definition? The code as is does not trigger it

[voodoos]

Huh, weird, my folder repro is literally just a file Repro.ml containing the code I have sent

Have you started typing a new definition? The code as is does not trigger it

I am not able to produce a stuck 100% cpu usage ocamllsp in the way you describe.

Could you enable verbose logging in the settings ? ocaml.trace.server is the name of the setting.
Then could you reload the window, bring it to the buggy state and share with us the content of the OCaml Language Server section in the OUTPUT panel ?

[qexat]

Okay, I figured the issue with my reproduction sample. The new definition needs to involve pattern matching specifically.

[Trace - 5:50:37 PM] Received response 'textDocument/foldingRange - (175)' in 1779ms. Request failed: cancelled (-32800).
[Trace - 5:50:38 PM] Received response 'textDocument/codeLens - (184)' in 1612ms.
Result: []


[Trace - 5:50:38 PM] Received response 'textDocument/documentSymbol - (178)' in 2686ms. Request failed: cancelled (-32800).
[Trace - 5:50:38 PM] Received response 'textDocument/signatureHelp - (174)' in 2920ms. Request failed: cancelled (-32800).
[Trace - 5:50:38 PM] Received response 'textDocument/documentSymbol - (177)' in 2688ms. Request failed: cancelled (-32800).
[Trace - 5:50:38 PM] Received response 'textDocument/inlayHint - (181)' in 1820ms. Request failed: cancelled (-32800).
[Trace - 5:50:50 PM] Sending notification '$/cancelRequest'.
Params: {
    "id": 180
}


[Trace - 5:50:50 PM] Sending notification '$/cancelRequest'.
Params: {
    "id": 182
}


[Trace - 5:50:50 PM] Received response 'textDocument/completion - (180)' in 14146ms. Request failed: cancelled (-32800).
[Trace - 5:50:50 PM] Received response 'textDocument/signatureHelp - (182)' in 14094ms. Request failed: cancelled (-32800).

[voodoos]

Thanks, I was able to reproduce and make the example even more minimal:

type t = ( :: )

let f (x: t) =  x

Placing the cursor on x here make the server loop. 🤦‍♂️

[qexat]

Nice, thank you!