Add handler for the output of atools

atools is a collection of tools written in ash shell and Lua that
provide linting for Alpine Linux's APKBUILD.

APKBUILDs are build recipes used by Alpine Linux's build system, abuild,
an equivalent would be Arch Linux's PKGBUILD and Gentoo's ebuild.

autoload/ale/handlers/atools.vim

@@ -0,0 +1,41 @@
+" Author: Leo <thinkabit.ukim@gmail.com>
+" Description: Handlers for output expected from atools
+
+function! ale#handlers#atools#Handle(buffer, lines) abort
+    " Format: SEVERITY:[TAG]:PATH:LINENUM:MSG
+    " Example: MC:[AL5]:./APKBUILD:12:variable set to empty string: install=
+    let l:pattern = '\([^:]\+\):\([^:]\+\):\([^:]\+\):\(\d\+\):\(.\+\)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        " We are expected to receive 2 characters, the first character
+        " can be 'S', 'I', 'M' 'T', which are respectively:
+        " Serious (Error)
+        " Important (Error)
+        " Minor (Warning)
+        " Style (Warning)
+        "
+        " The second character can be either 'C' or 'P', which are respectively:
+        " Certain (Error)
+        " Possible (Warning)
+        let l:severity = matchstr(l:match[1], '^.')
+        let l:certainty = matchstr(l:match[1], '.$')
+
+        let l:type = 'E'
+        " If the tag returns 'Minor' or 'Style' or is 'Possible'
+        " then return a warning
+
+        if l:severity is# 'M' || l:severity is# 'T' || l:certainty is# 'P'
+            let l:type = 'W'
+        endif
+
+        call add(l:output, {
+        \    'lnum': l:match[4] + 0,
+        \    'text': l:match[5],
+        \    'type': l:type,
+        \    'code': matchstr(l:match[2], 'AL[0-9]*'),
+        \})
+    endfor
+
+    return l:output
+endfunction