GoLang中的小“ a：”是什么意思？

In the JetBrains GoLand IDE, when I type a basic "Hello, World!" example, there is a small a: in front of the string passed to fmt.Println() that is added by the IDE. What does it mean and what is its purpose?

I could not find the answer in the documentation.

These are known as parameter hints, and they are common in JetBrains IDEs. Basically, it's the name of the parameter in the definition of fmt.Println. See the official docs, where the first parameter is named a in the definition of Println.