what is NextFeature used for

[zrwsmd]

i change my langium file rule(see below),it seems that auto complete provider didn't work out well,i write t1.a(or other t1.somecharacter),i debug and found it context.features length is 0，so it can't into this.completionFor(context, e, acceptor) method

so what is this context.features used for,how can i change code to let its length>0

[zrwsmd]

[zrwsmd]

change Function_invoke_or_assign rule from

Function_invoke_or_assign:
id=MemberCall  (assign=Assignment_subrule| params+=Invoke_subrule )*;

to

Function_invoke_or_assign:
(assignPrefix=AssignPrefix|id=MemberCall) (assign=Assignment_subrule | params+=Invoke_subrule)*;

-----------------------------------------------------------------------------------------------------------
AssignPrefix:
  varEnchanceDecl=[NamedElement:VarEnchanceDecl];


Assignment_subrule:
':=' (expression=Expression)* ;

MemberCall infers Expression:
    prior=Primary_Expression
	({infer MemberCall.previous=current}
        // Member call with function call
        ("." element=[NamedElement:VarEnchanceDecl] (
		explicitOperationCall?='('
		(
		    arguments+=Expression (',' arguments+=Expression)*
		)?
		')')?
        // Chained function call
        | (
		explicitOperationCall?='('
		(
		    arguments+=Expression (',' arguments+=Expression)*
		)?
		')'))
    )*;
Invoke_subrule:
'(' (parameters+=Param_assignment (',' parameters+=Param_assignment)*)?  ')';

Param_assignment:
(ParamName=VarEnchanceDecl InputOrOutputSign=(':='|'=>'))? (ParamValue=Expression)*;