Scala layer

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1. Description
- 1.1. Features:
2. Layer Installation
3. Backends
- 3.1. Metals
4. Scalastyle
- 4.1. Use Java doc-style
5. Enable Debug Adapter Protocol (DAP)
6. Automatically insert asterisk in multiline comments
7. Enable GTags as a fallback navigation utility
8. Key bindings
- 8.1. sbt

with

1. Description

This layer adds support for the Scala language to Spacemacs.

1.1. Features:

Syntax highlighting
Support for language backend using LSP and Metals
Debugging support via dap
Auto-completion
Treeview support for viewing project structure and triggering compilation
Syntax-checking
Refactoring
Incremental compilation
Style linting
Optional GGTags search

2. 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 on the Metals tree view side bar, set scala-auto-treeview to t.
To display SBT in a small buffer at the bottom of the frame, set the scala-sbt-window-position layer variable to bottom.

3. Backends

The only currently supported language backend is scala-metals. Support for Ensime has been dropped as that project has been dead for some time.

3.1. 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 0.9.8 can be replaced with the current version of Metals:

./coursier bootstrap \
  --java-opt -Xss4m \
  --java-opt -Xms100m \
  --java-opt -Dmetals.client=emacs \
  org.scalameta:metals_2.12:0.9.8 \
  -r bintray:scalacenter/releases \
  -r sonatype:snapshots \
  -o /usr/local/bin/metals-emacs -f

Notice that the layer by default overwrites Metals-scala tree view to nil. This to avoid issues with buffers when rendering VSCode like view, issue described Here.

You will then have the common LSP key bindings; see LSP#key-bindings for more details.

4. Scalastyle

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:

$ scalastyle
scalastyle 0.8.0
Usage: scalastyle [options] <source directory>
...

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

(setq-default flycheck-scalastylerc "/usr/local/etc/scalastyle_config.xml")

See the flycheck documentation and scalastyle configuration for up-to-date configuration instructions.

4.1. Use Java doc-style

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

(setq-default dotspacemacs-configuration-layers '(
  (scala :variables scala-indent:use-javadoc-style t)))

5. Enable Debug Adapter Protocol (DAP)

The metals backend enables integration with the DAP layer for debugging support.

6. 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.

(setq-default dotspacemacs-configuration-layers '(
  (scala :variables scala-auto-insert-asterisk-in-comments t)))

8. Key bindings

Additional major mode key bindings are populated by LSP and DAP.

8.1. sbt

Key binding	Description
`SPC m b .`	SBT transient state
`SPC m b b`	SBT command
`SPC m b c`	Run `compile` in SBT
`SPC m b t`	Run `test` in SBT
`SPC m b I`	Run `It / compile` in SBT
`SPC m b T`	Run `Test / compile` in SBT
`SPC m b =`	Run `scalafmtAll` in SBT

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