#+TITLE: Auto-Completion configuration layer for Spacemacs

* Table of Contents                                                   :TOC@4:
 - [[#description][Description]]
 - [[#install][Install]]
 - [[#configuration][Configuration]]
     - [[#key-bindings][Key bindings]]
     - [[#tooltips][Tooltips]]
     - [[#sort-results-by-usage][Sort results by usage]]
     - [[#enable-company-or-auto-complete-globally][Enable company or auto-complete globally]]
     - [[#replacing-company-by-auto-complete][Replacing company by auto-complete]]
     - [[#add-auto-completion-in-a-layer][Add auto-completion in a layer]]
 - [[#key-bindings][Key Bindings]]
     - [[#company][Company]]
     - [[#auto-complete][Auto-complete]]
     - [[#yasnippet][Yasnippet]]
     - [[#auto-yasnippet][Auto-yasnippet]]

* Description

This layer provides auto-completion to Spacemacs.

The following completion engines are supported:
- [[http://company-mode.github.io/][company]]
- [[http://auto-complete.org/][auto-complete]]

Snippets are supported via [[https://github.com/capitaomorte/yasnippet][yasnippet]] and [[https://github.com/abo-abo/auto-yasnippet][auto-yasnippet]].

This layer also configures =hippie-expand=.

* Install

To use this configuration layer add it to your =~/.spacemacs=

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(auto-completion))
#+END_SRC

* Configuration

** Key bindings

You can customize the user experience of auto-completion with the following
layer variables:

=auto-completion-return-key-behavior= set the action to perform when the
~RET~ key is pressed, the possible values are:
- =complete= completes with the current selection
- =nil= does nothing

=auto-completion-tab-key-behavior= set the action to perform when the
~TAB~ key is pressed, the possible values are:
- =complete= completes with the current selection
- =cycle= completes the common prefix and cycle between candidates
- =nil= does nothing

=auto-completion-complete-with-key-sequence= is a string of two characters
denoting a key sequence that will perform a =complete= action if the sequence
as been entered quickly enough. If its value is =nil= then the feature is
disabled.

The default configuration of the layer is:

#+BEGIN_SRC emacs-lisp
(setq-default dotspacemacs-configuration-layers '(
  (auto-completion :variables
                   auto-completion-return-key-behavior 'complete
                   auto-completion-tab-key-behavior 'cycle
                   auto-completion-complete-with-key-sequence nil)
                   ))
#+END_SRC

=jk= is a good candidate for =auto-completion-complete-with-key-sequence= if
you don't use it already.

** Tooltips

To enable docstring tooltips set =auto-completion-enable-help-tooltip= to =t=

#+BEGIN_SRC emacs-lisp
(setq-default dotspacemacs-configuration-layers
  '(auto-completion :variables
                    auto-completion-enable-help-tooltip t))
#+END_SRC

** Sort results by usage

To enable sorting auto-completion results by their usage frequency set
=auto-completion-enable-sort-by-usage= to =t=.
This feature is provided by the [[https://github.com/company-mode/company-statistics][company-statistics]] package when =company=
is used.
The variable has no effect when =auto-complete= is used.

#+BEGIN_SRC emacs-lisp
(setq-default dotspacemacs-configuration-layers
  '(auto-completion :variables
                    auto-completion-enable-sort-by-usage t))
#+END_SRC

** Enable company or auto-complete globally

By default Spacemacs enables auto-completion explicitly for each supported
major-mode, it means that =company= and =auto-complete= are not enabled
globally, it allows more flexibility to choose an auto-completion engine
for a given mode.

You may want to enable company globally to get auto-completion
everywhere even in the modes which are not configured by Spacemacs. To do
so, you just have to add =(global-company-mode)= in the
=dotspacemacs/config= function of your dotfile.

Note that if you want to enable =auto-complete= globally you will have to
disable =company= first, see the next section to do so.

** Replacing company by auto-complete

You can disable =company= by adding it to the =dotspacemacs-excluded-packages=
variable, then you are free to enable =auto-complete= globally.

** Add auto-completion in a layer

Here is an example to add =company= auto-completion to python buffer:

In =config.el=:

#+BEGIN_SRC emacs-lisp
  ;; Define the buffer local company backend variable
  (spacemacs|defvar-company-backends python-mode)
#+END_SRC

In =packages.el=:

#+BEGIN_SRC emacs-lisp
  ;; Add the relevant packages to the layer
  (setq python-packages
    '(...
      company
      company-anaconda
      ...))

  ;; Configure the packages
  (when (configuration-layer/layer-usedp 'auto-completion)

    ;; Hook company to python-mode
    (defun python/post-init-company ()
      (spacemacs|add-company-hook python-mode))

    ;; Add the backend to the major-mode specific backend list
    (defun python/init-company-anaconda ()
      (use-package company-anaconda
        :if (configuration-layer/package-usedp 'company)
        :defer t
        :init (push 'company-anaconda company-backends-python-mode))))
#+END_SRC

* Key Bindings

** Company

| Key Binding | Description                                                              |
|-------------+--------------------------------------------------------------------------|
| ~C-j~       | go down in company dropdown menu                                         |
| ~C-k~       | go up in company dropdown menu                                           |
| ~C-/~       | search in company dropdown                                               |
| ~C-M-/~     | filter the company dropdown menu                                         |
| ~C-d~       | open minibuffer with documentation of thing at point in company dropdown |

** Auto-complete

| Key Binding | Description                                                          |
|-------------+----------------------------------------------------------------------|
| ~C-j~       | select next candidate                                                |
| ~C-k~       | select previous candidate                                            |
| ~TAB~       | expand selection or select next candidate                            |
| ~S-TAB~     | select previous candidate                                            |
| ~return~    | complete word, if word is already completed insert a carriage return |

** Yasnippet

| Key Binding | Description                                                    |
|-------------+----------------------------------------------------------------|
| ~M-/~       | Expand a snippet if text before point is a prefix of a snippet |
| ~SPC i s~   | List all current yasnippets for inserting                      |

** Auto-yasnippet

| Key Binding | Description                                                               |
|-------------+---------------------------------------------------------------------------|
| ~SPC i S c~ | create a snippet from an active region                                    |
| ~SPC i S e~ | Expand the snippet just created with ~SPC i y~                            |
| ~SPC i S w~ | Write the snippet inside =private/snippets= directory for future sessions |