The service registry contains no services for the extension '' for language '...'

[AresEkb]

Here is a demo based on Langium 3.5:
https://github.com/AresEkb/langium-monaco-demo
https://aresekb.github.io/langium-monaco-demo/

I upgraded it to Langium 4.0.0:
https://github.com/AresEkb/langium-monaco-demo/tree/migrate-to-langium-4
And now get the error:
The service registry contains no services for the extension '' for language 'classmodel'
With the stacktrace:

getServices	@	service-registry.ts:97
parseAsync	@	documents.ts:315
update	@	documents.ts:302
(anonymous)	@	document-builder.ts:405
runCancelable	@	document-builder.ts:479
await in runCancelable		
buildDocuments	@	document-builder.ts:404
update	@	document-builder.ts:262
await in update		
(anonymous)	@	document-update-handler.ts:126
(anonymous)	@	workspace-lock.ts:96
Promise.then		
(anonymous)	@	workspace-lock.ts:96
performNextOperation	@	workspace-lock.ts:93
enqueue	@	workspace-lock.ts:74
write	@	workspace-lock.ts:59
(anonymous)	@	document-update-handler.ts:126
Promise.then		
fireDocumentUpdate	@	document-update-handler.ts:125
didChangeContent	@	document-update-handler.ts:134
(anonymous)	@	language-server.ts:282
invoke	@	events.js:55
fire	@	events.js:117
(anonymous)	@	normalized-text-documents.ts:218
handleNotification	@	connection.js:640
handleMessage	@	connection.js:342
processMessageQueue	@	connection.js:362
(anonymous)	@	connection.js:334
setTimeout		
setImmediate	@	ril.js:138
triggerMessageQueue	@	connection.js:332
callback	@	connection.js:405
invoke	@	events.js:55
fire	@	events.js:117
BrowserMessageReader._messageListener	@	main.js:32

Could you please help to fix it?

[cdietrich]

i assume you somewhere need to populate a
LanguageMetaData
in your language registration
https://github.com/AresEkb/langium-monaco-demo/blob/325d708d5846693748da7401fd5d2501df43f33b/src/dsl-editor/AbstractDslServer.ts#L64

see add. params for createServicesForGrammar

default impl is

const languageMetaData = config.languageMetaData ?? {
        caseInsensitive: false,
        fileExtensions: ['.txt'],
        languageId: grammarNode.name ?? 'UNKNOWN',
        mode: 'development'
    };

i cannot spot a "grammar classmodel" in your code

[AresEkb]

Thanks a lot! Addition of languageMetaData for createServicesForGrammar() fixed the error!