Automatic fixes with Oxlint LSP?

[FLchs]

Hello everyone,
I’m in the process of migrating from ESLint to Oxlint, but I’ve hit one missing feature.

Oxlint supports autofixes with the --fix flag, but the LSP doesn’t seem to provide any formatting capabilities, even though the source.fixAll.oxc command is available.

Did I miss something, or is this a feature that could be added to the LSP?

[camc314]

LSP doesn’t seem to provide any formatting capabilities

Are you referring to oxfmt (prettier like formatter)? If so, it's an LS option to configure it.

Or are you referring to format on save fixing fixable problems?

[FLchs]

LSP doesn’t seem to provide any formatting capabilities

Are you referring to oxfmt (prettier like formatter)? If so, it's an LS option to configure it.

No, to the oxlint LS. As stated in my initial message, it provides a source.fixAll.oxc command that I think is analogous to oxlint --fix, but as the LS doesn't return formating capabilities (as of LSP) I cannot setup a "apply autofix on save" without using source.fixAll.oxc.

Or are you referring to format on save fixing fixable problems?

I guess that's a good way to name it :)

[Sysix]

source.fixAll.oxc is a code action, the same is the oxc.fixAll command.
Did you add the following snippet to your .vscode/settings.json?

  "editor.codeActionsOnSave": {
    "source.fixAll.oxc": "always"
  }

It should work 🤞 , we have a test for it:

oxc/editors/vscode/tests/code_actions.spec.ts

Lines 85 to 112 in 8c85e08

	// https://github.com/oxc-project/oxc/issues/10422
	test('code action `source.fixAll.oxc` on editor.codeActionsOnSave', async () => {
	const file = Uri.joinPath(fixturesWorkspaceUri(), 'fixtures', 'file.js');
	const expectedFile = Uri.joinPath(fixturesWorkspaceUri(), 'fixtures', 'expected.txt');
	await workspace.getConfiguration('editor').update('codeActionsOnSave', {
	'source.fixAll.oxc': 'always',
	});
	await workspace.saveAll();
	const range = new Range(new Position(0, 0), new Position(0, 0));
	const edit = new WorkspaceEdit();
	edit.replace(file, range, ' ');
	await sleep(1000);
	await loadFixture('fixall_with_code_actions_on_save');
	await workspace.openTextDocument(file);
	await workspace.applyEdit(edit);
	await sleep(1000);
	await workspace.saveAll();
	await sleep(500);
	const content = await workspace.fs.readFile(file);
	const expected = await workspace.fs.readFile(expectedFile);
	strictEqual(content.toString(), expected.toString());
	});

[FLchs]

Ok thank you, I'm sorry for the confusion I should have emphasized on the fact that my question was specifically about the LS and not about the VSCode extension. I'm using Neovim native LSP client.

I now understand that the LS provides a fixAll comand that is to be used by the editor, not a formatting capability in the LSP sense. So I could replicate the VSCode extension feature using a simple autocmd :

vim.api.nvim_create_autocmd("BufWritePre", {
	desc = "Format before save",
	pattern = "*",
	group = vim.api.nvim_create_augroup("FormatConfig", { clear = true }),
	callback = function(ev)
		local client = vim.lsp.get_clients({ name = "oxlint", bufnr = ev.buf })[1]

		if not client then
			return
		end

		local request_result = client:request_sync("workspace/executeCommand", {
			command = "oxc.fixAll",
			arguments = {
				{
					uri = vim.uri_from_bufnr(ev.buf),
				},
			},
		})

		if request_result and request_result.err then
			vim.notify(request_result.err.message, vim.log.levels.ERROR)
			return
		end

	end,
})

So now it works as expected, only issue I get now is how can I change the LS settings?
I tried many formats but it always errors as it fails to deserialize my settings... And I'm not able to understand how the settings are forwarded to LS from the VScode extension.

vim.lsp.config("oxlint", {
	cmd = { "oxc_language_server" },
	cmd_env = {
		RUST_LOG = "debug",
	},
	settings = {
		initializationOptions = {
			{
				workspaceUri = "file://home/francois/Projects/Personal/project",
				options = {
					["fmt.experimental"] = true,
				},
			},
		},
	},
})

[ERROR][2025-12-05 13:07:42] ...p/_transport.lua:36	"rpc"	"oxc_language_server"	"stderr"	'[2025-12-05T12:07:42Z DEBUG oxc_language_server::backend] oxc initialized.
[2025-12-05T12:07:42Z DEBUG oxc_language_server::worker] 
            configuration changed:
            incoming: Object {"initializationOptions": Array [Object {"workspaceUri": String("file://home/francois/Projects/Personal/project"), "options": Object {"fmt.experimental": Bool(true)}}]}
            current: Null
            
'
[ERROR][2025-12-05 13:07:42] ...p/_transport.lua:36	"rpc"	"oxc_language_server"	"stderr"	"[2025-12-05T12:07:42Z WARN  oxc_language_server::formatter::server_formatter] Failed to deserialize LSPFormatOptions from JSON: no object passed, falling back to default options
"

I'm not understand why it complains, in the VSCode Oxc channel the settings are passed with the same format :

Any idea of the format expected?

[Sysix]

configuration changed:

This output only happens when the editor sends the workspace/didChangeConfiguration notification.
Another problem: It looks like the initializationOptions inside in initialize request is not set correctly (current: Null).

Try this setting:

	settings = {
		{
			workspaceUri = "file://home/francois/Projects/Personal/project",
			options = {
				["fmt.experimental"] = true,
			},
		},
	},

This reflects what the editor expects for workspace/didChangeConfiguration params:
https://github.com/oxc-project/oxc/tree/main/crates/oxc_language_server#workspacedidchangeconfiguration
After that notification, the server should restart its internal tools and respect your new configuration (from null to object)

[Sysix]

When you're using Neovim, you can maybe try https://github.com/oxc-project/coc-oxc too. :)

[FLchs]

configuration changed:

This output only happens when the editor sends the workspace/didChangeConfiguration notification. Another problem: It looks like the initializationOptions inside in initialize request is not set correctly (current: Null).

Try this setting:

	settings = {
		{
			workspaceUri = "file://home/francois/Projects/Personal/project",
			options = {
				["fmt.experimental"] = true,
			},
		},
	},

It seems to error less indeed but I'm not sure my settings are used,
I set it to :

settings = {
  {
	  options = {
		  ["fmt.experimental"] = true,
		  ["fixKind"] = "all",
	  },
  },
},

But dangerous_fix-able errors don't get autofixed.

for (var i = 0; i < 10; i--) { //does not get autofixed https://oxc.rs/docs/guide/usage/linter/rules/eslint/for-direction.html
  console.log(i);
}

debugger; // get autofixed https://oxc.rs/docs/guide/usage/linter/rules/eslint/for-direction.html

And formating doesn't work but I guess there is something that the extension does that I should do too...

When you're using Neovim, you can maybe try https://github.com/oxc-project/coc-oxc too. :)
I would rather stick with native LSP support, it works great with the other LS.

[Sysix]

The workspaceUri is the important key. Looks like it still falls back to the default configuration.

And formating doesn't work but I guess there is something that the extension does that I should do too...

In VS Code you need to define your formatter. The Editor can have multiple extensions which could support formatting.
It is a config setting like "editor.defaultFormatter": "extension.name"

[FLchs]

The workspaceUri is the important key. Looks like it still falls back to the default configuration.

Yes probably, but it should not...

And formating doesn't work but I guess there is something that the extension does that I should do too...

In VS Code you need to define your formatter. The Editor can have multiple extensions which could support formatting. It is a config setting like "editor.defaultFormatter": "extension.name"

I'm not using VSCode :/

Indeed document formatting is advertised by the LS, but calling formatting does nothing (probably because fmt.experimental is false for the reason you stated).

{
  codeActionProvider = {
    codeActionKinds = { "quickfix", "source.fixAll.oxc" }
  },
  documentFormattingProvider = true, // <--
  executeCommandProvider = {
    commands = { "oxc.fixAll" }
  },
  textDocumentSync = {
    change = 1,
    openClose = true,
    save = {
      includeText = false
    }
  },
  workspace = {
    workspaceFolders = {
      changeNotifications = true,
      supported = true
    }
  }
}