Implement an Interface in Go with just the LSP

Have you ever wanted to a simple way to implement a Go interface? If you wanted to do this in the past you would have had to use a tool like impl or in Neovim use go.nvim which has a builtin command using this program.

In recent years this functionality is available directly in the Go LSP gopls but it is a little difficult to find. I found this out myself nestled in the comments of a gopls feature request on the projects Github Issues page.

This method will work for both VS Code and Neovim granted you have the language server setup already.

Implementing an interface through a code action

type Dog interface {
	Bark()
}

type Animal struct {
	name string
}

To get the code action to appear we need to create a statement that will not compile because of the static type not does not implement the interface.

var dog Dog = Animal{} // error : Animal does not implement Dog (missing method Bark)

var dog Dog = new(Animal)

Now hovering the error in neovim and requsting code acions from the LSP you will see the option Declare missing methods of Dog and selecting it will result in the following:

type Animal struct {
	name string
}

// Bark implements Dog.
func (a Animal) Bark() {
	panic("unimplemented")
}

🎉 TADA 🎉

We have generated the method stubs for the type using just the LSP, no third party tools necessary.