Common prefix problem in content assist

[cdietrich]

Hi,

we have a grammar like this

MetadataElementPropertyDefinition:ID] ':' value=(STRING|ID|INT);

hidden terminal WS: /\s+/;
terminal ID: /[_a-zA-Z][\w_]*/;
terminal INT returns number: /[0-9]+/;
terminal STRING: /"(\\.|[^"\\])*"|'(\\.|[^'\\])*'/;

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

and our scoping that looks like (simplified)

import { AstNode, AstUtils, DefaultScopeProvider, EMPTY_SCOPE, ReferenceInfo, Scope } from "langium";
import { isMetadataPropertyAssignment } from "./generated/ast.js";

export class HelloScopeProvider extends DefaultScopeProvider {
    override getScope(context: ReferenceInfo): Scope {
        if (context.property === 'property' && isMetadataPropertyAssignment(context.container)) {
            const document = AstUtils.getDocument(context.container);
            return this.createScopeForNodes([
                {
                    $type: "MetadataElementPropertyDefinition",
                    name: "active",
                    $document: document
                } as any as AstNode,
                {
                    $type: "MetadataElementPropertyDefinition",
                    name: "description",
                    $document: document
                } as any as AstNode
            ])
        }
        return EMPTY_SCOPE;
    }
}

but the content assist does not behave as expected as this tests shows

import {  describe, test } from "vitest";
import { EmptyFileSystem } from "langium";
import { expectCompletion } from "langium/test";
import { createHelloWorldServices } from "../../src/language/hello-world-module.js";


describe('completion tests', () => {

    test('test no error simple model', async () => {
        const services = createHelloWorldServices(EmptyFileSystem).HelloWorld;
        const ec = expectCompletion(services);

        await ec({
            text: `
@metadata { 
    <|>
    
}
composite type MyComposite {
    name Text
}
            `,
            expectedItems: ["active", "description"],
            index: 0,
        })
    });

    test('test the error simple model', async () => {
        const services = createHelloWorldServices(EmptyFileSystem).HelloWorld;
        const ec = expectCompletion(services);

        await ec({
            text: `
@metadata { 
    active: true
    <|>
    
}
composite type MyComposite {
    name Text
}
            `,
            expectedItems: ["active", "description"], // why is this empty
            index: 0,
        })
    });
});

is there a way to circument the problem and guide the content assist parser
or is such common prefix grammars not possible with langium?

[msujew]

This is essentially a duplicate of #1798. It is supposed to work, the internal engine that is supposed to resolve such cases is just currently not capable of going into a rulecall and leaving it again.

[cdietrich]

possible workaround

entry Model:
    (persons+=ModelContent)*;


ModelContent: 
     ('@metadata' '{' (content+=MetadataPropertyAssignment)* '}')? MetadataVisibility? 
     ({infer CompositeTypeDefinition} 'composite' 'type' name=ID ('extends' baseType=ID)? '{' (content+=CompositeTypeMember)* '}'
    |
{infer PrimitiveTypeDefinition} 'primitive' 'type' name=ID ('extends' baseType=ID)? '{' '}')
    ;