#+TITLE: GO layer

#+TAGS: general|layer|multi-paradigm|programming

[[file:img/go.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#install][Install]]
  - [[#pre-requisites][Pre-requisites]]
  - [[#lsp-backend][LSP backend]]
  - [[#layer][Layer]]
- [[#configuration][Configuration]]
  - [[#indentation][Indentation]]
  - [[#tests][Tests]]
  - [[#guru][Guru]]
  - [[#autocomplete][Autocomplete]]
- [[#working-with-go][Working with Go]]
  - [[#go-commands-start-with-m][Go commands (start with =m=):]]
  - [[#go-guru][Go Guru]]
  - [[#refactoring][Refactoring]]

* Description
This layer adds extensive support for go to Spacemacs.

** Features:
- gofmt/goimports on file save (to enable, see [[#configuration][Configuration]])
- Auto-completion using [[https://github.com/nsf/gocode/tree/master/emacs][go-autocomplete]] (with the =auto-completion= layer)
- Source analysis using [[https://docs.google.com/document/d/1_Y9xCEMj5S-7rv2ooHpZNH15JgRT5iM742gJkw5LtmQ][go-guru]]
- Refactoring with [[http://gorefactor.org/][godoctor]]
- Edit struct field tag with [[https://github.com/fatih/gomodifytags][gomodifytags]]
- Linting with flycheck's built-in checkers or flycheck-gometalinter
- Coverage profile visualization
- Test generation with [[https://github.com/s-kostyaev/go-gen-test][go-gen-test]]
- Get packages faster with [[https://github.com/haya14busa/gopkgs][gopkgs]]
- Fill a structure with default values using the [[https://github.com/davidrjenni/reftools/tree/master/cmd/fillstruct][fillstruct]]
- LSP backend

* Install
** Pre-requisites
You will need =gocode=, =gogetdoc=, =godef=, =godoctor= and many others
to get all the goodies of this layer:

#+BEGIN_SRC sh
  go get -u -v github.com/mdempsky/gocode
  go get -u -v github.com/rogpeppe/godef
  go get -u -v golang.org/x/tools/cmd/guru
  go get -u -v golang.org/x/tools/cmd/gorename
  go get -u -v golang.org/x/tools/cmd/goimports
  go get -u -v golang.org/x/tools/cmd/godoc
  go get -u -v github.com/zmb3/gogetdoc
  go get -u -v github.com/cweill/gotests/...
  go get -u github.com/haya14busa/gopkgs/cmd/gopkgs
  go get -u -v github.com/davidrjenni/reftools/cmd/fillstruct
  go get -u github.com/josharian/impl
#+END_SRC

If you wish to use a linters aggregator tool, you can enable =gometalinter= or =golangci-lint=.

If you wish to use =gometalinter= set the value of =go-use-gometalinter= to t:

#+BEGIN_SRC emacs-lisp
  (go :variables go-use-gometalinter t)
#+END_SRC

and install the tool:

#+BEGIN_SRC sh
  go get -u -v github.com/alecthomas/gometalinter
  gometalinter --install --update
#+END_SRC

For more information read [[https://github.com/alecthomas/gometalinter/blob/master/README.md][gometalinter README.md]]
and [[https://github.com/favadi/flycheck-gometalinter/blob/master/README.md][flycheck-gometalinter README.md]]

If you wish to use =golangci-lint= set the value of =go-use-golangci-lint= to t:

#+BEGIN_SRC emacs-lisp
  (go :variables go-use-golangci-lint t)
#+END_SRC

and install the tool:

#+BEGIN_SRC sh
  go get -u github.com/golangci/golangci-lint/cmd/golangci-lint
#+END_SRC

For more information read [[https://github.com/golangci/golangci-lint][golangci-lint README.md]]
and [[https://github.com/weijiangan/flycheck-golangci-lint][flycheck-golangci-lint README.md]]

If you wish to use =godoctor= for refactoring, install it too:

#+BEGIN_SRC sh
  go get -u -v github.com/godoctor/godoctor
  go install github.com/godoctor/godoctor
#+END_SRC

If you want to use =gomodifytags= to edit field tags, install it too:

#+BEGIN_SRC sh
  go get -u -v github.com/fatih/gomodifytags
#+END_SRC

Make sure that the =gocode= executable is in your PATH. For information about
setting up =$PATH=, check out the corresponding section in the FAQ (~SPC h f
$PATH RET~).

For best results, make sure that the =auto-completion= and =syntax-checking=
layers are enabled as well.

** LSP backend
To enable the LSP backend set the layer variable =go-backend=:

#+BEGIN_SRC elisp
  (go :variables go-backend 'lsp)
#+END_SRC

You also need to install the Go Language Server.
Consult the installation command for the desired language server found at [[https://www.github.com/emacs-lsp/lsp-mode/][lsp-mode]] for instructions.

Backend can be chosen on a per project basis using directory local variables
(files named =.dir-locals.el= at the root of a project), an example to use the
=go-mode= backend:

#+BEGIN_SRC elisp
  ;;; Directory Local Variables
  ;;; For more information see (info "(emacs) Directory Variables")

  ((go-mode (go-backend . go-mode)))
#+END_SRC

*Note:* you can easily add a directory local variable with ~SPC f v d~.

** Layer
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =go= to the existing =dotspacemacs-configuration-layers= list in this
file.

* Configuration
To run =gofmt= before save, set the value to a non-nil, e.g.

#+BEGIN_SRC emacs-lisp
  (setq go-format-before-save t)
#+END_SRC

To use a different formatter, set the value of =gofmt-command=, e.g.

#+BEGIN_SRC emacs-lisp
  (setq gofmt-command "goimports")
#+END_SRC

or

#+BEGIN_SRC emacs-lisp
  (go :variables gofmt-command "goimports")
#+END_SRC

To run current main package with command line arguments, set the value of
=go-run-args= as file local variable, e.g.

#+BEGIN_SRC emacs-lisp
  // Local Variables:
  // go-run-args: "--output run.log"
  // End:
#+END_SRC

** Indentation
By default, the tab width in Go mode is 8 spaces. To use a different value set
the layer variable =go-tab-width=, e.g.

#+BEGIN_SRC emacs-lisp
  (go :variables go-tab-width 4)
#+END_SRC

If you're using =.editorconfig= in your project, set the value to nil to avoid
confliction, e.g.

#+BEGIN_SRC emacs-lisp
  (go :variables go-tab-width nil)
#+END_SRC

** Tests
If you're using =gocheck= in your project you can use the
=go-use-gocheck-for-testing= variable to enable suite testing and to get single
function testing to work.

=go-coverage-display-buffer-func= controls how =go-coverage= should display
the coverage buffer. See [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Choosing-Window.html][=display-buffer=]] for a list of possible functions.
The default value is =display-buffer-reuse-window=.

Tests are run in a compilation buffer displayed in a popup window that can be
closed by pressing ~C-g~ from any other window. The variable
=go-test-buffer-name= can be customized to set the output buffer name.

To provide additional arguments to go test, specify =go-use-test-args=.

#+BEGIN_SRC emacs-lisp
  (go :variables go-use-test-args "-race -timeout 10s"
#+END_SRC

** Guru
Go Oracle has been deprecated as of October 1, 2016, it's replacement is =go-guru=.

If you would like to use the =goguru= bindings in your work, you will need to
install it, and in your project you will need to set the scope with ~SPC m f o~.
The scope is a comma separated set of packages, and =go=’s recursive operator is
supported. In addition, you can prefix with =-= to exclude a package from
searching.

In addition, =GOPATH= must be set prior to =go-guru= initialization.

** Autocomplete
For auto-completion there are actually two choices. First there is the classic =gocode=.
This has been around for quite a long time now, however =gocode= has many shortcomings like
not being able to show documentation for build-in objects or being fully dependent on installed binary
files to provide its suggestions.

A more modern and complete solution is provided by =gogetdoc= which is able to
precisely detect all documentations in your go projects independent on where
they have been added. This is also the choice recommended from =go-mode.el=.

To choose =gocode= nothing more needs to be done. To use =gogetdoc= you need to set

#+BEGIN_SRC emacs-lisp
  (go :variables godoc-at-point-function 'godoc-gogetdoc)
#+END_SRC

in your =dotfile=.

If you choose to use =gocode= there are some suggestions to improve its results.
As =gocode= uses the output from installed binary files to provide its suggestions.
You have a few options to ensure you always get up to date suggestions:
- Run =go install ./...= in your package directory when you make a file change.
- Run =gocode set autobuild true= to have gocode attempt to run =go install ./...=
  for you.
- You can configure your task runner to run =go install ./...= command on every
  file change.

* Working with Go
** Go commands (start with =m=):

| Key binding   | Description                                                                           |
|---------------+---------------------------------------------------------------------------------------|
| ~SPC m =~     | run "go fmt"                                                                          |
| ~SPC m e b~   | go-play buffer                                                                        |
| ~SPC m e d~   | download go-play snippet                                                              |
| ~SPC m e r~   | go-play region                                                                        |
| ~SPC m g a~   | jump to matching test file or back from test to code file                             |
| ~SPC m g c~   | open a clone of the current buffer with a coverage info (=go tool cover -h= for help) |
| ~SPC m g g~   | go jump to definition                                                                 |
| ~SPC m h h~   | godoc at point                                                                        |
| ~SPC m i a~   | add import                                                                            |
| ~SPC m i g~   | goto imports                                                                          |
| ~SPC m i r~   | remove unused import                                                                  |
| ~SPC m r n~   | go rename                                                                             |
| ~SPC m t P~   | run "go test" for the current package and all packages under it                       |
| ~SPC m t g f~ | generate tests for all exported functions                                             |
| ~SPC m t g F~ | generate tests for all functions                                                      |
| ~SPC m t g g~ | DWIM generate test for the function in the active region                              |
| ~SPC m t p~   | run "go test" for the current package                                                 |
| ~SPC m t s~   | run "go test" for the suite you're currently in (requires gocheck)                    |
| ~SPC m t t~   | run "go test" for the function you're currently in (while you're in a _.test.go file) |
| ~SPC m x x~   | run "go run" for the current 'main' package                                           |

** Go Guru

| Key binding | Description                                          |
|-------------+------------------------------------------------------|
| ~SPC m f <~ | go-guru show possible callers                        |
| ~SPC m f >~ | go-guru show call targets                            |
| ~SPC m f c~ | go-guru show channel sends/receives                  |
| ~SPC m f d~ | go-guru describe symbol at point                     |
| ~SPC m f e~ | go-guru show possible contants/types for error value |
| ~SPC m f f~ | go-guru show free variables                          |
| ~SPC m f i~ | go-guru show implements relation                     |
| ~SPC m f j~ | go-guru jump to symbol definition                    |
| ~SPC m f o~ | go-guru set analysis scope                           |
| ~SPC m f p~ | go-guru show what the select expression points to    |
| ~SPC m f r~ | go-guru show referrers                               |
| ~SPC m f s~ | go-guru show callstack                               |

** Refactoring

| Key binding | Description                                                     |
|-------------+-----------------------------------------------------------------|
| ~SPC m r d~ | Add comment stubs                                               |
| ~SPC m r e~ | Extract code as new function                                    |
| ~SPC m r f~ | Add field tags                                                  |
| ~SPC m r F~ | Remove field tags                                               |
| ~SPC m r i~ | Generate method stubs for implementing an interface (=go-impl=) |
| ~SPC m r n~ | Rename (with =godoctor=)                                        |
| ~SPC m r N~ | Rename (with =go-rename=)                                       |
| ~SPC m r s~ | Fill structure with default values                              |
| ~SPC m r t~ | Toggle declaration and assignment                               |