Go中用括号括起来的变量声明语法是什么？

I am trying to find some information on parenthesis enclosed variable declaration syntax in Go but maybe I just do not know its name and that's why I cannot find it (just like with e.g. value and pointer receivers).

Namely I would like to know the rules behind this type of syntax:

package main

import (
    "path"
)

// What's this syntax ? Is it exported ? 
var (
    rootDir = path.Join(home(), ".coolconfig")
)

func main() {
  // whatever
}

Are those variables in var () block available in modules that import this one?

This code

// What's this syntax ? Is it exported ? 
var (
    rootDir = path.Join(home(), ".coolconfig")
)

is just a longer way of writing

var rootDir = path.Join(home(), ".coolconfig")

However it is useful when declaring lots of vars at once. Instead of

var one string
var two string
var three string

You can write

var (
    one string
    two string
    three string
)

The same trick works with const too.

var (...) (and const (...) are just shorthand that let you avoid repeating the var keyword. It doesn't make a lot of sense with a single variable like this, but if you have multiple variables it can look nicer to group them this way.

It doesn't have anything to do with exporting. Variables declared in this way are exported (or not) based on the capitalization of their name, just like variables declared without the parentheses.