How to solve the import-local-package problem: GOPATH is ignored, only GOROOT takes effects

I'm new in GO and has got stuck in environment configuration for hours.

I succeeded to run some test projects, but when I tried to import my custom local packages (say xxx), the "go run" command failed, logging that:

*test/main/main.go:6:2: package test/xxx is not in GOROOT (/usr/local/go/src/test/xxx)*

It is strange that GOPATH seems to be ignored when importing local packages on my ubuntu computer.

go version is go1.16.5 linux/amd64

GOPATH is set using export GOPATH="$HOME/GoProjects"

GOROOT is set using export GOPATH="/usr/local/go"

GoMod is "on" using go env -w GO111MODULE=on

After editing project's .go files, command "go mod init" and "go mod tidy" are typed in the root folder of the project ($GOPATH/src/test), and the project file structure looks like:

/src
  /.vscode
    -launch.json
  /gitbub.com
  /test
    /main
      -main.go     (here: import "test/xxx")
    /xxx
      -xxx.go      (here: package xxx)
    -go.mod        (almost empty - line 1: module test
                                   line 2: 
                                   line 3: go 1.16     )

What should I do to fix this problem?

Solution

First, stop worrying about GOPATH. That is old stuff, and you don't need to do it any more. Then, make a folder somewhere test (doesn't need to be anything to do with GOPATH, just put in current directory, or wherever you want). Then make test/xxx. Then make test/xxx/xxx.go:

package xxx

const X = 1

Then make folder test/main. Then make test/main/main.go:

package main
import "test/xxx"

func main() {
   println(xxx.X)
}

Then go back to test, and do go mod init test. Then go back to test/main, and do go build. Done.