#+TITLE: Scala layer

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

[[file:img/scala.png]] with [[file:img/ensime.png]]

* Table of Contents                     :TOC_5_gh:noexport:
- [[#description][Description]]
  - [[#features][Features:]]
- [[#layer-installation][Layer Installation]]
- [[#backends][Backends]]
  - [[#metals][Metals]]
  - [[#ensime-deprecated][Ensime (deprecated)]]
    - [[#installation-when-using-sbt][Installation when using SBT]]
    - [[#installation-when-using-gradle][Installation when using Gradle]]
    - [[#configuration][Configuration]]
    - [[#usage][Usage]]
- [[#scalastyle][Scalastyle]]
  - [[#use-java-doc-style][Use Java doc-style]]
- [[#enable-debug-adapter-protocol-dap][Enable Debug Adapter Protocol (DAP)]]
- [[#automatically-show-the-type-of-the-symbol-under-the-cursor][Automatically show the type of the symbol under the cursor]]
- [[#automatically-insert-asterisk-in-multiline-comments][Automatically insert asterisk in multiline comments]]
- [[#deprecated-automatic-replacement-of-arrows-with-unicode-ones][Deprecated: Automatic replacement of arrows with Unicode ones]]
- [[#enable-gtags-as-a-fallback-navigation-utility][Enable GTags as a fallback navigation utility]]
- [[#auto-start][Auto-start]]
- [[#key-bindings][Key bindings]]
  - [[#ensime][Ensime]]
    - [[#search][Search]]
    - [[#ensime-search-mode][Ensime Search Mode]]
    - [[#sbt][sbt]]
    - [[#typecheck][Typecheck]]
    - [[#debug][Debug]]
    - [[#errors][Errors]]
    - [[#goto][Goto]]
    - [[#print-and-yank-types][Print and yank types]]
    - [[#documentation-inspect][Documentation, Inspect]]
    - [[#server][Server]]
    - [[#refactoring][Refactoring]]
    - [[#tests][Tests]]
    - [[#repl][REPL]]

* Description
This layer adds support for the Scala language to Spacemacs.

** Features:
- Syntax highlighting
- Support for language backend. Either using [[https://ensime.github.io/][ENSIME]] or [[https://scalameta.org/metals/][Metals]]
- Debugging support via dap
- Auto-completion
- Treeview support for viewing project structure and triggering compilation
- Syntax-checking
- Refactoring
- Incremental compilation
- Scala Repl
- Style linting
- Eldoc integration
- Optional GGTags search
- Test execution directly from Emacs
- Automatic replacement of ASCII arrows with unicode ones

* Layer Installation
To use this configuration layer, add it to your =~/.spacemacs=. You will need to
add =scala= to the existing =dotspacemacs-configuration-layers= list in this
file.
+ To turn off the Metals tree view side bar, set =scala-auto-treeview= to =nil=.
+ To display SBT in a small buffer at the bottom of the frame, set the
  =scala-sbt-window-position= layer variable to =bottom=.

* Backends
The currently supported language backends are:
- scala-metals
- scala-ensime (deprecated)

To set your choice of backend, configure the layer variable =scala-backend=.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers
                '((scala :variables scala-backend 'scala-metals))) ;or 'scala-ensime
#+END_SRC

** Metals
Currently, you must manually install the metals server. It is possible to do so
via coursier; the latest version can be built using the following commands,
where =0.7.6= can be replaced with the current version of [[https://github.com/scalameta/metals/][Metals]]:

#+BEGIN_SRC bash
  ./coursier bootstrap \
    --java-opt -Xss4m \
    --java-opt -Xms100m \
    --java-opt -Dmetals.client=emacs \
    org.scalameta:metals_2.12:0.7.6 \
    -r bintray:scalacenter/releases \
    -r sonatype:snapshots \
    -o /usr/local/bin/metals-emacs -f
#+END_SRC

You will then have the common LSP key bindings; see
[[https://github.com/syl20bnr/spacemacs/tree/develop/layers/%2Btools/lsp#key-bindings][LSP#key-bindings]] for more details.

** Ensime (deprecated)
This package is mainly unmaintained today and should only be used as a last resort.

[[https://ensime.github.io/][ENSIME]] provides IDE-like features, such as refactoring, incremental compilation
and project-wide type-checking.

You will also need to modify your =dotspacemacs/user-init= to pull the recommended Ensime
version (Stable):

#+BEGIN_SRC emacs-lisp
  (add-to-list 'configuration-layer-elpa-archives '("melpa-stable" . "stable.melpa.org/packages/"))
  (add-to-list 'package-pinned-packages '(ensime . "melpa-stable"))
#+END_SRC

ENSIME requires a configuration file at the root of each Scala project. It
provides an SBT plugin, a gradle plugin and others (see [[https://web.archive.org/web/20190427005241/https://ensime.github.io/build_tools/][ensime.org]] for a full
list) to generate these files.

*** Installation when using SBT
Find it with your favourite package manager, eg:

#+BEGIN_SRC shell
  nix-env --install sbt
#+END_SRC

or refer to [[http://www.scala-sbt.org/download.html][the sbt installation instructions]].

*** Installation when using Gradle
Refer to the [[https://web.archive.org/web/20190324005432/http://ensime.github.io/build_tools/gradle/][Ensime installation instructions]] to install the =ensime-gradle=
plugin.

*** Configuration
Follow [[https://web.archive.org/web/20190417132406/http://ensime.github.io/build_tools/sbt/][the ENSIME configuration instructions]]. Spacemacs uses
the development version of Ensime so follow the appropriate steps.

To use the build functions under ~SPC m b~ you need to use version =0.13.5= or
newer of =sbt=, and specify that in your project's =project/build.properties=.
For example,

#+BEGIN_SRC scala
  sbt.version=0.13.11
#+END_SRC

*** Usage
~SPC SPC spacemacs/ensime-gen-and-restart~ or ~SPC m D r~ generates a new config
for a project and starts the server. Afterwards ~SPC SPC ensime~ or ~SPC m D s~
will suffice do the trick.

* Scalastyle
[[http://www.scalastyle.org/][Scalastyle]] provides style-checking and linting. The Emacs functionality is
provided by Flycheck.

To use scalastyle, it must be present as an executable in your =PATH=.
- macOS users: =brew install scalastyle=
- Linux, please see [[http://www.scalastyle.org/command-line.html]]

To test if =scalastyle= executable is in your path, run =scalastyle= in a new
terminal, it should output something like:

#+BEGIN_SRC bash
  $ scalastyle
  scalastyle 0.8.0
  Usage: scalastyle [options] <source directory>
  ...
#+END_SRC

Finally, enable the =syntax-checking= layer and set the =flycheck-scalastylerc=
variable to a valid location.

#+BEGIN_SRC emacs-lisp
  (setq-default flycheck-scalastylerc "/usr/local/etc/scalastyle_config.xml")
#+END_SRC

See the [[http://www.flycheck.org/en/latest/languages.html?highlight=scala#syntax-checker-scala-scalastyle][flycheck documentation]] and [[http://www.scalastyle.org/configuration.html][scalastyle configuration]] for up-to-date
configuration instructions.

** Use Java doc-style
To enable =java-doc-style=, set the variable =scala-indent:use-javadoc-style= to
=t=

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (scala :variables scala-indent:use-javadoc-style t)))
#+END_SRC

* Enable Debug Adapter Protocol (DAP)
The metals backend enables integration with the DAP layer for debugging support.

* Automatically show the type of the symbol under the cursor
To enable the feature =ensime-type-at-point= when cursor moves, set the
variable =scala-enable-eldoc= to =t=.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (scala :variables scala-enable-eldoc t)))
#+END_SRC

Enabling this option can cause slow editor performance.

* Automatically insert asterisk in multiline comments
To insert a leading asterisk in multiline comments automatically, set the
variable =scala-auto-insert-asterisk-in-comments= to =t=.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (scala :variables scala-auto-insert-asterisk-in-comments t)))
#+END_SRC

* Deprecated: Automatic replacement of arrows with Unicode ones
Scala used to support Unicode arrows =⇒=, =→= as aliases for ~=>~, =->= and =<-=, and the
Scala layer would do the conversion to Unicode for you if you set
=scala-use-unicode-arrows= to =t=. As the Unicode arrows are now [[https://github.com/scala/scala/pull/7540][deprecated]] in
Scala, this variable has been dropped from the Scala layer. If it is still in
your Scala layer variables like so:

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (scala :variables scala-use-unicode-arrows t)))
#+END_SRC

Then you will need to remove it:

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

* Enable GTags as a fallback navigation utility
To enable gtags when in scala-mode, in case metals, or, ensime are not fully
functioning set the variable =scala-enable-gtags= to =t=.

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
    (scala :variables scala-enable-gtags t)))
#+END_SRC

* Auto-start
If you prefer to have the backend start when you load a scala file, you can enable it
with

#+BEGIN_SRC emacs-lisp
  (setq-default dotspacemacs-configuration-layers '(
      (scala :variables scala-auto-start-backend t)))
#+END_SRC

* Key bindings
** Ensime
*** Search

| Key binding | Description                                         |
|-------------+-----------------------------------------------------|
| ~SPC m /~   | incremental search using =ensime-scalex= major mode |
| ~SPC m ?~   | incremental search in all live buffers              |

*** Ensime Search Mode

| Key binding | Description                                                       |
|-------------+-------------------------------------------------------------------|
| ~C-j~       | Move to next match                                                |
| ~C-k~       | Move to previous match                                            |
| ~C-i~       | Insert at point import of current result                          |
| ~RET~       | Jump to the target of the currently selected ensime-search-result |
| ~C-q~       | Quit ensime search                                                |

*** sbt

| Key binding | Description         |
|-------------+---------------------|
| ~SPC m b .~ | sbt transient state |
| ~SPC m b b~ | sbt command         |
| ~SPC m b c~ | compile             |
| ~SPC m b C~ | clean command       |
| ~SPC m b i~ | switch to sbt shell |
| ~SPC m b p~ | package command     |
| ~SPC m b r~ | run command         |

*** Typecheck

| Key binding | Description                 |
|-------------+-----------------------------|
| ~SPC m c t~ | type check the current file |

*** Debug

| Key binding | Description                 |
|-------------+-----------------------------|
| ~SPC m d A~ | Attach to a remote debugger |
| ~SPC m d b~ | set breakpoint              |
| ~SPC m d B~ | clear breakpoint            |
| ~SPC m d C~ | clear all breakpoints       |
| ~SPC m d c~ | continue                    |
| ~SPC m d i~ | inspect value at point      |
| ~SPC m d n~ | next                        |
| ~SPC m d o~ | step out                    |
| ~SPC m d q~ | quit                        |
| ~SPC m d r~ | run                         |
| ~SPC m d s~ | step                        |
| ~SPC m d t~ | backtrace                   |

*Note:* These key bindings need a transient-state, PR welcome :-)

*** Errors

| Key binding | Description                                        |
|-------------+----------------------------------------------------|
| ~SPC m e e~ | print error at point                               |
| ~SPC m e s~ | switch to buffer containing the stack trace parser |

*** Goto

| Key binding | Description      |
|-------------+------------------|
| ~SPC m g g~ | go to definition |

*** Print and yank types

|-------------+--------------------------------|
| ~SPC m h T~ | print full type name at point  |
| ~SPC m h t~ | print short type name at point |
| ~SPC m y T~ | yank full type name at point   |
| ~SPC m y t~ | yank short type name at point  |

*** Documentation, Inspect

| Key binding | Description                            |
|-------------+----------------------------------------|
| ~SPC m h h~ | show documentation for symbol at point |
| ~SPC m h u~ | show uses for symbol at point          |

*** Server

| Key binding | Description                                            |
|-------------+--------------------------------------------------------|
| ~SPC m D f~ | reload open files                                      |
| ~SPC m D r~ | regenerate the =.ensime= and restart the ensime server |
| ~SPC m D s~ | start ensime server                                    |

*** Refactoring

| Key binding | Description                                                          |
|-------------+----------------------------------------------------------------------|
| ~SPC m r a~ | add type annotation                                                  |
| ~SPC m r d~ | get rid of an intermediate variable (=ensime-refactor-inline-local=) |
| ~SPC m r D~ | get rid of an intermediate variable (=ensime-undo-peek=)             |
| ~SPC m r i~ | organize imports                                                     |
| ~SPC m r m~ | extract a range of code into a method                                |
| ~SPC m r r~ | rename a symbol project wide                                         |
| ~SPC m r t~ | import type at point                                                 |
| ~SPC m r v~ | extract a range of code into a variable                              |
| ~SPC m z~   | expand/contract region                                               |

*** Tests

| Key binding | Description              |
|-------------+--------------------------|
| ~SPC m t a~ | test command (sbt)       |
| ~SPC m t r~ | test quick command (sbt) |
| ~SPC m t t~ | test only (sbt)          |

*** REPL

| Key binding | Description                                                         |
|-------------+---------------------------------------------------------------------|
| ~SPC m s a~ | ask for a file to be loaded in the REPL                             |
| ~SPC m s b~ | send buffer to the REPL                                             |
| ~SPC m s B~ | send buffer to the REPL and focus the REPL buffer in =insert state= |
| ~SPC m s i~ | start or switch to the REPL inferior process                        |
| ~SPC m s r~ | send region to the REPL                                             |
| ~SPC m s R~ | send region to the REPL and focus the REPL buffer in =insert state= |