go build報錯cannot find package

go env 關鍵數據是這樣的

GOPATH="/home/zzy/goProject"
GOROOT="/usr/local/go"

項目目錄是這樣的

goProject
├── bin
├── pkg
└── src
    └── go_learn
            └── day01
                ├── hello
                │   ├── hello
                │   └── hello.go
                └── str_type
                    ├── str.go
                    └── world.go

hello.go我的代碼是這樣的

package main

import (
    "fmt"
    "go_learn/day01/str_type/world"    ## 這句導入包，一直報錯
)
func main()  {
    fmt.Print("hello world")
    test()
}

world.go代碼是這樣的

package main

import "fmt"

func test()  {
    fmt.Print("啦啦啦啦")

}

go build 報錯是這樣的

$ go build
hello.go:5:2: cannot find package "go_learn/day01/str_type/world" in any of:
        /usr/local/go/src/go_learn/day01/str_type/world (from $GOROOT)
        /home/zzy/goProject/src/go_learn/day01/str_type/world (from $GOPATH)

最后解決了！十分low的一個問題，估計初學者才會犯

world.go文件內容改一下就可以

package  world  # 是個文件，不是包，不要導入main

import "fmt"

# 函數名大寫，就可以在外面引用該函數
func Test()  {
    fmt.Println("lll")
    
}