Creating a submodule with go-git

main.go

package main

import (
	"fmt"
	"log"
	"strings"
	"time"

	"gopkg.in/src-d/go-billy.v4/memfs"
	git "gopkg.in/src-d/go-git.v4"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
	"gopkg.in/src-d/go-git.v4/storage/memory"
)

func checkerr(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func main() {
	mem := make(memory.ModuleStorage)
	s, err := mem.Module("foo")
	checkerr(err)

	fs := memfs.New()
	f, err := fs.Create(".gitmodules")
	checkerr(err)
	fmt.Fprintln(f, strings.Join([]string{
		"[submodule \"go-git\"]",
		"\tpath = include/go-git",
		"\turl = git@github.com:src-d/go-git.git"}, "\n"))
	checkerr(f.Close())

	repo, err := git.Init(s, fs)
	checkerr(err)

	wt, err := repo.Worktree()

	_, err = wt.Add(".gitmodules")
	checkerr(err)
	_, err = wt.Commit("creating submodule", &git.CommitOptions{
		Author: &object.Signature{
			Name:  "Francesc",
			Email: "francesc@sourced.tech",
			When:  time.Now(),
		},
	})
	checkerr(err)

	sms, err := wt.Submodules()
	checkerr(err)
	for _, sm := range sms {
		cfg := sm.Config()
		fmt.Println(cfg.Name, cfg.URL, cfg.Branch)
	}
}