Go modules without remote repository?

Question

I'm trying to get Go modules working without involving a remote repository.

src is a local directory that contains all my projects, also projects that are written in other languages than Go. For simplicity I have only show the two directories relevant for my question:

src
 ├── client
 │   ├── go.mod
 │   └── main.go
 └── lib
     ├── go.mod
     └── lib.go

The go.mod files are created by running the command go mod init client in src/client and go mod init lib in src/lib.

src/client/main.go:

package main

import "lib"

func main() {
    lib.Hello()
}

src/lib/lib.go:

package lib

import "fmt"

func Hello() {
    fmt.Println("Hello World")
}

What I'm trying to do is using the library lib.go in my main.go, but no matter what I put in the import path, this error is shown:

main.go:3:8: package lib is not in GOROOT (/usr/lib/go/src/lib)

Go version is go1.14.3

How do I correctly import Go code from local folders?

Answer 1

You can use replace directive.

Project structure:

root
 ├── client
 │   ├── go.mod
 │   └── main.go
 └── lib
     ├── go.mod
     └── lib.go

go.mod of root/lib module:

module github.com/owner/root/lib

go 1.13

go.mod of root/client module:

module github.com/owner/root/client

go 1.13

require github.com/owner/root/lib v0.0.0

replace github.com/owner/root/lib => ../lib

This is terrible, do you really have to do this for every import if there is no VCS?

No. replace directive replaces the contents of a specific version of a module and includes packages that belong to substitute module.

root
 ├── client
 │   ├── go.mod
 │   └── main.go
 └── lib
     ├── utils
     │   └── util.go
     ├── libs
     │   └── lib.go
     └── go.mod

package main

import (
    "github.com/owner/root/lib/utils"
    "github.com/owner/root/lib/libs"
)

func main() {
    //...
}