code: func NewAggFuncDesc(ctx sessionctx.Context, name string, args []expression.Expression, hasDistinct bool) *AggFuncDesc {
  	b := newBaseFuncDesc(ctx, name, args)
  	return &AggFuncDesc{baseFuncDesc: b, HasDistinct: hasDistinct}
  }
docs: // NewAggFuncDesc creates an aggregation function signature descriptor.