Add basic scala support using scalac (#56)

* Add basic scala support using scalac

* Convert if to a ternary expression

* Better bounds check

* Code formatting

* Mention Scala in the documentation

ale_linters/scala/scalac.vim

@@ -0,0 +1,58 @@
+" vim: set et:
+" Author: Zoltan Kalmar - https://github.com/kalmiz
+" Description: Basic scala support using scalac
+
+if exists('g:loaded_ale_linters_scala_scalac')
+    finish
+endif
+
+let g:loaded_ale_linters_scala_scalac = 1
+
+function! ale_linters#scala#scalac#Handle(buffer, lines)
+    " Matches patterns line the following:
+    "
+    " /var/folders/5q/20rgxx3x1s34g3m14n5bq0x80000gn/T/vv6pSsy/0:26: error: expected class or object definition
+    let pattern = '^.\+:\(\d\+\): \(\w\+\): \(.\+\)'
+    let output = []
+    let ln = 0
+
+    for line in a:lines
+        let ln = ln + 1
+        let l:match = matchlist(line, pattern)
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        let text = l:match[3]
+        let type = l:match[2] == 'error' ? 'E' : 'W'
+        let col = 0
+        if ln + 1 < len(a:lines)
+            let col = stridx(a:lines[ln + 1], '^')
+            if col == -1
+                let col = 0
+            endif
+        endif
+
+        " vcol is Needed to indicate that the column is a character.
+        call add(output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[1] + 0,
+        \   'vcol': 0,
+        \   'col': col + 1,
+        \   'text': text,
+        \   'type': type,
+        \   'nr': -1,
+        \})
+    endfor
+
+    return output
+endfunction
+
+call ALEAddLinter('scala', {
+\   'name': 'scalac',
+\   'executable': 'scalac',
+\   'output_stream': 'stderr',
+\   'command': g:ale#util#stdin_wrapper . ' .scala scalac -Ystop-after:parser',
+\   'callback': 'ale_linters#scala#scalac#Handle',
+\})