Golang - package name as double underscore

In my protobuf generated go code, the package is:

package __

What does the double underscore mean, does it means the same as folder name ?

Is there a document for this, I searched but didn't found any. And the code can compile without error.

Yes it means the same directory. Let's look at the following code.

Directory Structure

.
├── go.mod
├── greet
│   └── greet.go
└── main.go

Content in greet.go

package __

import "fmt"

func Hello(name string) {
	fmt.Printf("Hello %s\n", name)
}

Content in main.go

package main

import greet "playground/greet"

func main() {
	greet.Hello("Eric")
}

Current Directory

$ pwd
/Users/thedatageek/Codes/go-playground

Unfortunately I also couldn't find any docs for go.

But it seems that its kinda good thing. You really don't need to name the package. You just name the directory and the package name would be automatically the same.

Note: This is definitely not the grpc or protobuf thing. It is however a customary that if you have generated proto stub from a proto file and if you add some additional utility file you may put those into a dir and then import it directly via directory name. For example the following github repos

https://github.com/Ash110/gRPC-Logger
https://github.com/dist1ll/cache-prototype
https://github.com/kamensotirov99/int-gateway
https://github.com/rachaelyychen/go-gee
https://github.com/suvvm/ToadOCREngine
https://github.com/denyami/drawing-api

What I found about package __ (double underscore):

• When import such package, must specify alias, can't omit, otherwise can't find the package.
• When import, editor (e.g goland) can't auto search, must import by hand.

So, I guess __ means no name or no default name.

Update - better avoid it.

After using __ for a while, I would suggest to avoid it.
Because the IDE can't find it by package name.
It's inconvenient, especially when u want to reuse functions in the package.