Understanding type inference

[cdietrich]

given the grammar

grammar HelloWorld

entry Model:
    (persons+=ModelContent)*;

ModelContent: (('@metadata' '{' (props+=MetadataPropertyAssignment)* '}')? (
    {infer StructTypeDefinition}StructTypeDefinition | 
    {infer SimpleTypeDefinition}SimpleTypeDefinition)) | Other;

Other: "other" name=ID;

StructTypeMember:
    ('@metadata' '{' (props+=MetadataPropertyAssignment)* '}')? (optional?='optional')? name=ID type=ID;

fragment MetadataVisibility:
    visibility=('private'|'internal'|'public');


fragment StructTypeDefinition:
    MetadataVisibility? 'struct' 'type' name=ID ('extends' baseType=ID)? '{' (content+=StructTypeMember)* '}'
;

fragment SimpleTypeDefinition:
    MetadataVisibility? 'simple' 'type' name=ID ('extends' baseType=ID)? '{' '}'
;

interface MetadataElementPropertyDefinition {
    name: string;
}

MetadataPropertyAssignment:
    property=[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]*/;

i would expect to find props and visibility in both SimpleTypeDefinition and StructTypeDefinition
but i dont. is this a bug? a feature?
is there a better way (with keeping content assist for MetadataPropertyAssignment working for the 2nd element?

[msujew]

Hey @cdietrich,

Likely a bug somewhere in the type inference. I believe as a workaround, StructTypeDefinition and SimpleTypeDefinition could be interfaces that add visibility?: ... and props: MetadataPropertyAssignment[]. AFAIK that should work as expected:

ModelContent: (('@metadata' '{' (props+=MetadataPropertyAssignment)* '}')? (
    {StructTypeDefinition} StructTypeDefinitionRule | ...;

interface StructTypeDefinition {
    visibility?: 'private' | 'internal' | 'public';
    props?: MetadataPropertyAssignment[];
    name: string;
    baseType?: string;
    content: StructTypeMember[];
}