docs(scala): add post about using vim as scala ide

autoload/SpaceVim/layers/lang/scala.vim

@@ -129,7 +129,7 @@ scriptencoding utf-8
 "
 " 1.  To make neoformat support scala file, you should install scalariform.
 "     [`scalariform`](https://github.com/scala-ide/scalariform)
-"     and set 'g:spacevim_layer_lang_scala_formatter' to the path of the jar.
+"     and set `scalariform_jar` option to the path of the jar.
 "
 " 2.  If lsp [`metals-vim`](https://scalameta.org/metals/docs/editors/overview.html)
 "     is enabled, it will automatically use 
@@ -137,6 +137,12 @@ scriptencoding utf-8
 "     to format code.
 
 
+if exists('s:scalariform_jar')
+  finish
+endif
+
+let s:scalariform_jar = ''
+
 function! SpaceVim#layers#lang#scala#plugins() abort
   let plugins = [ 
         \ ['derekwyatt/vim-scala', {'on_ft': 'scala'}],
@@ -163,7 +169,7 @@ function! SpaceVim#layers#lang#scala#config() abort
   let g:neoformat_enabled_scala = neoformat#formatters#scala#enabled()
   let g:neoformat_scala_scalariform = {
         \ 'exe': 'java',
-        \ 'args': ['-jar', get(g:,'spacevim_layer_lang_scala_formatter', ''), '-'],
+        \ 'args': ['-jar', s:scalariform_jar, '-'],
         \ 'stdin': 1,
         \ }
 endfunction
@@ -336,6 +342,9 @@ endfunction
 
 " vim:set et sw=2 cc=80:
 
+function! SpaceVim#layers#lang#scala#set_variable(var) abort
+  let s:scalariform_jar = get(a:var, 'scalariform_jar', s:scalariform_jar)
+endfunction
 
 function! SpaceVim#layers#lang#scala#health() abort
   call SpaceVim#layers#lang#scala#plugins()

doc/SpaceVim.txt

@@ -4708,7 +4708,7 @@ CODE FORMATTING
 
   1. To make neoformat support scala file, you should install scalariform.
     [`scalariform`](https://github.com/scala-ide/scalariform) and set
-    'g:spacevim_layer_lang_scala_formatter' to the path of the jar.
+    `scalariform_jar` option to the path of the jar.
 
   2. If lsp
     [`metals-vim`](https://scalameta.org/metals/docs/editors/overview.html) is

docs/_posts/2022-04-24-use-vim-as-a-scala-ide.md

@@ -0,0 +1,77 @@
+---
+title: "Use Vim as a Scala IDE"
+categories: [tutorials, blog]
+description: "A general guide for using SpaceVim as Scala IDE, including layer configuration, requiems installation and usage."
+type: article
+comments: true
+commentsID: "Use Vim as a Scala IDE"
+---
+
+# [Blogs](../blog/) >> Use Vim as a Scala IDE
+
+This is a general guide for using SpaceVim as a Scala IDE, including layer configuration and usage. 
+Each of the following sections will be covered:
+
+### Enable language layer
+
+`lang#scala` layer provides scala language specific features for SpaceVim.
+This layer is not enabled by default. To write scala language,
+you need to enable the `lang#scala` layer.
+Press `SPC f v d` to open SpaceVim configuration file, and add following configuration:
+
+```toml
+[[layers]]
+  name = 'lang#scala'
+```
+
+for more info, you can read the [lang#scala](../layers/lang/scala/) layer documentation.
+
+### code completion
+
+By default the autocomplete layer has been enabled, so after loading `lang#scala` layer, the code completion
+for scala language should work well.
+
+
+### alternate file jumping
+
+To manage the alternate file for a project, you may need to create a `.project_alt.json` file in the root of your
+project.
+
+for example, add following content into the `.project_alt.json` file:
+
+```json
+{
+  "src/*.scala": {"alternate": "test/{}.scala"},
+  "test/*.scala": {"alternate": "src/{}.scala"}
+}
+```
+
+with this configuration, you can jump between the source code and test file via command `:A`
+
+
+### code running
+
+The key binding for running current file is `SPC l r `, it will run `sbt run` asynchronously.
+And the stdout will be shown on a runner buffer.
+
+
+### REPL support
+
+Start a `scala` inferior REPL process with `SPC l s i`. After REPL process started,
+you can send code to `scala` process via key bindings:
+
+| Key Bindings | Descriptions                                     |
+| ------------ | ------------------------------------------------ |
+| `SPC l s b`  | send buffer and keep code buffer focused         |
+| `SPC l s l`  | send line and keep code buffer focused           |
+| `SPC l s s`  | send selection text and keep code buffer focused |
+
+
+### code format
+
+The code formation feature is provided by `format` layer, and this layer is enabled by default.
+The default format engine is `neoformat`, it will run `scalafmt` or `scalariform`
+asynchronously on current file.
+
+To use scalariform, you need to install [`scalariform`](https://github.com/scala-ide/scalariform).
+and set `scalariform_jar` option to the path of the scalariform jar.