How can I automatically add dependency packages to go.mod

Question

I have modifed an existing github project with dozens of 3rd party imported packages but I kept the basic structure intact, which is like this:

.
├── config
│   ├── config.json
│   └── mysql.sql
├── gowebapp.go
├── LICENSE
├── README.md
├── static
├── template
│   ├── about
│   │   └── about.tmpl
│   ├── base.tmpl
└── vendor
    └── app
        ├── controller
        │   ├── about.go
        │   ├── error.go
        │   ├── index.go
        │   ├── login.go
        │   ├── notepad.go
        │   ├── register.go
        │   └── static.go
        ├── model
        │   ├── model.go
        │   ├── note.go
        │   └── user.go
        ├── route
        │   ├── middleware
        │   │   ├── acl
        │   │   │   └── acl.go
        │   │   ├── httprouterwrapper
        │   │   │   └── httprouterwrapper.go
        │   │   ├── logrequest
        │   │   │   └── logrequest.go
        │   │   └── pprofhandler
        │   │       └── pprofhandler.go
        │   └── route.go
        └── shared
            ├── database
            │   └── database.go
            ├── email
            │   └── email.go
            ├── jsonconfig
            │   └── jsonconfig.go
            ├── passhash
            │   ├── passhash.go
            │   └── passhash_test.go
            ├── recaptcha
            │   └── recaptcha.go
            ├── server
            │   └── server.go
            ├── session
            │   └── session.go
            └── view
                ├── plugin
                │   ├── noescape.go
                │   ├── prettytime.go
                │   └── taghelper.go
                └── view.go

Now I want to use go modules to make the project portable.

The main.go imports are like:

    package main

    import (
    "encoding/json"
    "log"
    "os"
    "runtime"

    "app/route"
    "app/shared/database"
    "app/shared/email"
    "app/shared/jsonconfig"
    "app/shared/recaptcha"
    "app/shared/server"
    "app/shared/session"
    "app/shared/view"
    "app/shared/view/plugin"
)

As you can see the code mostly sits in vendor/app folder.

I have added several other packages to that.

The problem is that manually adding the packages to go.mod is so tedious, and after all I may miss some imports.

So I'm wondering if there are some automatic tricks to fetch the dependencies to go.mod?

Answer 1

Initialize the module with go mod init module-path, this will create the go.mod file. Build the project with go build. It automatically adds all dependencies to go.mod, transitively.

No manual step is involved. The go tool does everything for you. Of course you may edit the go.mod file and "fine-tune" the included versions if the automatically chosen ones do not fit your need / intent. See Version Selection how it is done by default.

Note that starting with Go 1.16, go mod tidy might be needed to add depencencies.