This is a basic layout for Go application projects. It's not an official standard defined by the core Go dev team; however, it is a set of common historical and emerging project layout patterns in the Go ecosystem. Some of these patterns are more popular than others. It also has a number of small enhancements along with several supporting directories common to any large enough real world application.
If you are trying to learn Go or if you are building a PoC or a toy project for yourself this project layout is an overkill. Start with something really simple (a single `main.go` file is more than enough). As your project grows keep in mind that it'll be important to make sure your code is well structured otherwise you'll end up with a messy code with lots of hidden dependencies and global state. When you have more people working on the project you'll need even more structure. That's when it's important to introduce a common way to manage packages/libraries. When you have an open source project or when you know other projects import the code from your project repository that's when it's important to have private (aka `internal`) packages and code. Clone the repository, keep what you need and delete everything else! Just because it's there it doesn't mean you have to use it all. None of these patterns are used in every single project. Even the `vendor` pattern is not universal.
If you need help with naming, formatting and style start by running [`gofmt`](https://golang.org/cmd/gofmt/) and [`golint`](https://github.com/golang/lint). Also make sure to read these Go code style guidelines and recommendations:
Don't put a lot of code in the application directory. If you think the code can be imported and used in other projects, then it should live in the `/pkg` directory. If the code is not reusable or if you don't want others to reuse it, put that code in the `/internal` directory. You'll be surprised what others will do, so be explicit about your intentions!
Private application and library code. This is the code you don't want others importing in their applications or libraries. Note that this layout pattern is enforced by the Go compiler itself. See the Go 1.4 [`release notes`](https://golang.org/doc/go1.4#internalpackages) for more details.
You can optionally add a bit of extra structure to your internal packages to separate your shared and non-shared internal code. It's not required (especially for smaller projects), but it's nice to have visual clues showing the intended package use. Your actual application code can go in the `/internal/app` directory (e.g., `/internal/app/myapp`) and the code shared by those apps in the `/internal/pkg` directory (e.g., `/internal/pkg/myprivlib`).
Library code that's ok to use by external applications (e.g., `/pkg/mypubliclib`). Other projects will import these libraries expecting them to work, so think twice before you put something here :-)
It's also a way to group Go code in one place when your root directory contains lots of non-Go components and directories making it easier to run various Go tools (as mentioned in the [`Best Practices for Industrial Programming`](https://www.youtube.com/watch?v=PTE4VJIdHPg) from GopherCon EU 2018).
See the [`/pkg`](pkg/README.md) directory if you want to see which popular Go repos use this project layout pattern. This is a common layout pattern, but it's not universally accepted and some in the Go community don't recommend it.
Put your CI (travis, circle, drone) configurations and scripts in the `/build/ci` directory. Note that some of the CI tools (e.g., Travis CI) are very picky about the location of their config files. Try putting the config files in the `/build/ci` directory linking them to the location where the CI tools expect them (when possible).
Additional external test apps and test data. Feel free to structure the `/test` directory anyway you want. For bigger projects it makes sense to have a data subdirectory. For example, you can have `/test/data` or `/test/testdata` if you need Go to ignore what's in that directory. Note that Go will also ignore directories or files that begin with "." or "_", so you have more flexibility in terms of how you name your test data directory.
Some Go projects do have a `src` folder, but it usually happens when the devs came from the Java world where it's a common pattern. If you can help yourself try not to adopt this Java pattern. You really don't want your Go code or Go projects to look like Java :-)
Don't confuse the project level `/src` directory with the `/src` directory Go uses for its workspaces as described in [`How to Write Go Code`](https://golang.org/doc/code.html). The `$GOPATH` environment variable points to your (current) workspace (by default it points to `$HOME/go` on non-windows systems). This workspace includes the top level `/pkg`, `/bin` and `/src` directories. Your actual project ends up being a sub-directory under `/src`, so if you have the `/src` directory in your project the project path will look like this: `/some/path/to/workspace/src/your_project/src/your_code.go`. Note that with Go 1.11 it's possible to have your project outside of your `GOPATH`, but it still doesn't mean it's a good idea to use this layout pattern.
* [Go Report Card](https://goreportcard.com/) - It will scan your code with `gofmt`, `go vet`, `gocyclo`, `golint`, `ineffassign`, `license` and `misspell`. Replace `github.com/golang-standards/project-layout` with your project reference.
* [GoDoc](http://godoc.org) - It will provide online version of your GoDoc generated documentation. Change the link to point to your project.
* Release - It will show the latest release number for your project. Change the github link to point to your project.
