Autocompletion for optional keyword

[boxer-code]

Hi everyone! I'm struggling with the autocompletion for one keyword. Just for the one "behaviour". It is the only optional one. That's why I think that this is the problem. Do I have to handle optional keywords different?
This is the grammar:

grammar Flex

entry FlexModel:
    useStatement=UseStatement 
    faultStatements+=FaultStatement*; 

UseStatement: 
     'Use' 'simulator' simulator=SIMULATOR 'with' 'map' map=ID'.';

FaultStatement:
    'Fault' fault=FAULTTYPE (behaviour=Behaviour)? 'in' timeRange=TimeRange '.';

Behaviour: 
    type=BEHAVIOURTYPE severity=DECIMAL;

 TimeRange: 
        '[' startTime=INT ',' endTime=INT ']' time=TIMEUNIT;


hidden terminal WS: /\s+/;
terminal SIMULATOR: /fssim|fsds/; 
terminal FAULTTYPE: 'control/engine_damage' | 
    'control/fast_slam';
terminal TIMEUNIT: /seconds|milliseconds/;
terminal BEHAVIOURTYPE: /torque_limit_fraction/;
terminal ID: /[_a-zA-Z][\w_]*/;
terminal DECIMAL: /[0-9]+\.[0-9]+/;
terminal INT returns number: /[0-9]+/;
terminal STRING: /"(\\.|[^"\\])*"|'(\\.|[^'\\])*'/;

hidden terminal ML_COMMENT: /\/\*[\s\S]*?\*\//;
hidden terminal SL_COMMENT: /\/\/[^\n\r]*/;

This is the completion file:

import { CompletionItemKind} from "vscode-languageserver"
import { CompletionAcceptor, NextFeature } from "langium/lsp";
import { DefaultCompletionProvider,  CompletionContext} from "langium/lsp";
import type { FlexServices } from './flex-module.js';

export function registerCompletionProvider(services: FlexServices) {
    const provider = new FlexCompletionProvider(services);
    services.lsp.CompletionProvider = provider;
}

export class FlexCompletionProvider extends DefaultCompletionProvider {

    protected override async completionFor(context: CompletionContext, next: NextFeature, acceptor: CompletionAcceptor): Promise<void> {
        await super.completionFor(context, next, acceptor);
        
        if (next.property === "simulator" && context.node?.$type === "UseStatement") {
            acceptor(context, {
                label: "fssim",
                kind: CompletionItemKind.Value,
            });
            acceptor(context, {
                label: "fsds",
                kind: CompletionItemKind.Value,
            });
        }

        if (next.property === "fault" && context.node?.$type === "FaultStatement") {
            acceptor(context, {
                label: "control/engine_damage",
                kind: CompletionItemKind.Value,
            });
            acceptor(context, {
                label: "control/fast_slam",
                kind: CompletionItemKind.Value,
            });
        }

        if (next.property === "behaviour" && context.node?.$type === "FaultStatement") {
            acceptor(context, {
                label: "torque_limit_fraction",
                kind: CompletionItemKind.Value,
            });
        }

        if (next.property === "time" && context.node?.$type === "TimeRange") {
            acceptor(context, {
                label: "seconds",
                kind: CompletionItemKind.Value,
            });
            acceptor(context, {
                label: "milliseconds",
                kind: CompletionItemKind.Value,
            });
        }
    }
}

Thanks in advance!

[cdietrich]

hi, what is the expected behaviour and the actual?
besides that BEHAVIOURTYPE is no keyword
as it in a terminal and not a datatype rule

[cdietrich]

maybe you can play around with

export class HelloWorldCompletionProvider extends DefaultCompletionProvider {

    protected override continueCompletion(items: CompletionItem[]): boolean {
        return true
    }

    protected override performNextTokenCompletion(document: LangiumDocument, text: string, _offset: number, _end: number): boolean {
        return true;
    }

[msujew]

As @cdietrich said, the issue is likely that BEHAVIOURTYPE is no keyword. We cannot offer completion for terminals that aren't cross references, since they are internally just regex. We can assert that an input matches that regex, but the inverse (i.e. proposing a text that matches the regex) is only possible if the terminal is used for a cross reference.

[boxer-code]

Ah, thank you very much! Now I understood the problem.