From https://tip.golang.org/doc/go1.5 --

The WaitGroup function in package sync now diagnoses code that races a call to Add against a return from Wait. If it detects this condition, WaitGroup panics.

WaitGroup is a type, not a function. In looking at the race-related code in the WaitGroup.Add() and WaitGroup.Wait() methods, I think this line in the docs is supposed to read more like:

sync.WaitGroup's Add method now diagnoses code that races a call to Add against a return from Wait. If it detects this condition, Add panics.