go-eldoc.el provides eldoc for Go language. go-eldoc.el shows type information for variable, functions and current position of function.

• gocode
• go-mode

You can install go-mode with package.el from MELPA. And you can install gocode by go get as below.

% go get -u github.com/nsf/gocode

You can install go-eldoc.el from MELPA with package.el.

(require 'package)
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
(package-initialize)
(package-refresh-contents)

evaluate this code and M-x package-install go-eldoc.

Call go-eldoc-setup function at go-mode-hook

(require 'go-eldoc) ;; Don't need to require, if you install by package.el
(add-hook 'go-mode-hook 'go-eldoc-setup)

You can change face of current argument position by eldoc-highlight-function-argument like this.

(set-face-attribute 'eldoc-highlight-function-argument nil
                    :underline t :foreground "green"
                    :weight 'bold)

gocode location. You need not to set this variable if you set ($GOPATH/bin) to PATH environment variable correctly.