具有联合声明/赋值运算符的全局变量内联赋值和另一个未声明的变量丢失范围？

This Go program will not compile. It throws the error global_var declared and not used

package main

import "log"

var global_var int

func main() {

    global_var, new_string := returnTwoVars()

    log.Println("new_string: " + new_string)
}

func returnTwoVars() (int, string) {
    return 1234, "woohoo"
}

func usesGlobalVar() int {
    return global_var * 2
}

However, when I remove the need for using the := operator by declaring new_string in the main function and simply using =, the compiler doesn't have a problem with seeing that global_var is declared globally and being used elsewhere in the program. My intuition tells me that it should know that global_var is declared already

The compiler doesn't complain about the global_var outside main. It only complains about the newly created global_var in main that you don't use. Which you can check by looking at the line number that go mentions.

You can try an empty program with a global_var outside any function that nobody references: no problems there. And of course, the usesGlobalVar function that does reference the actual global symbol has nothing to do with the one you create in main.