Lookahead problems with (composite?) rules

[cdietrich]

when porting from langium we have a grammar excerpt like

grammar Repro;

interface Root { Value composite }

composite ID: RawId | EscapedId;
composite QualifiedName: ID ("." ID)*;   // greedy — consumes all dot-separated IDs
composite PATH: ID ("/" ID)* ":" ID | ID;
composite QualifiedPATH: QualifiedName "::" PATH | PATH;

token RawId:     /[_a-zA-Z][\w_-]*/;
token EscapedId: /`[^`]*`/;
hidden token WS: /[ \t\r\n]+/;

Root returns Root:
    Value=QualifiedPATH;

and expect to be able to parse

Input	Expected QualifiedPATH result	Notes
myId	myId	plain PATH (single ID)
some/path:node	some/path:node	PATH with slash+colon
pkg::node	pkg::node	single-segment qualified name
a.b.c::node	a.b.c::node	multi-segment qualified name

but

myId

does not parse

extended to

EnumMemberValue returns EnumMemberValue:
    "enum-member" "<" EnumRef=QualifiedPATH "." MemberName=ID ">";

enum-member<EntityType.LegalEntity> also does not parse

[msujew]

Fastbelt currently still uses LL(k) lookahead. This is expected and will be fixed once we support LL(*).