Add support for shellcheck linting.

plugin/ale/handlers.vim

@@ -0,0 +1,40 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: This file defines some standard error format handlers. Any
+"   linter which outputs warnings and errors in a format accepted by one of
+"   these functions can simply use one of these pre-defined error handlers.
+
+if exists('g:loaded_ale_handlers')
+    finish
+endif
+
+let g:loaded_ale_handlers = 1
+
+function! ale#handlers#HandleGCCFormat(buffer, lines)
+    " Look for lines like the following.
+    "
+    " <stdin>:8:5: warning: conversion lacks type at end of format [-Wformat=]
+    " <stdin>:10:27: error: invalid operands to binary - (have ‘int’ and ‘char *’)
+    " -:189:7: note: $/${} is unnecessary on arithmetic variables. [SC2004]
+    let pattern = '^[^:]\+:\(\d\+\):\(\d\+\): \([^:]\+\): \(.\+\)$'
+    let output = []
+
+    for line in a:lines
+        let l:match = matchlist(line, pattern)
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        call add(output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[1] + 0,
+        \   'vcol': 0,
+        \   'col': l:match[2] + 0,
+        \   'text': l:match[4],
+        \   'type': l:match[3] ==# 'error' ? 'E' : 'W',
+        \   'nr': -1,
+        \})
+    endfor
+
+    return output
+endfunction