"The assigned type is not compatible with the declared property" with enum-like type

[ebousse]

Langium version: 4.1.0
Package name: ?

Steps To Reproduce

1. Write the grammar below
2. Run npm run langium:generate

Code example:

grammar HelloWorld

interface Root {
    color: Color
}

type Color = 'red' | 'blue' | 'green';


entry RootRule returns Root:
    'color' color=ColorRule
;

ColorRule returns Color:
    'red' | 'blue' | 'green'
;

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

The current behavior

src/hello-world.langium:11:13 - The assigned type 'ColorRule' is not compatible with the declared property 'color' of type 'Color'.

Screenshot:

The expected behavior

The grammar should work without type error.

[msujew]

Thanks for the report, see #2076 for a fix.