Fix #510 Support checking LESS files with stylelint

ale_linters/less/stylelint.vim

@@ -0,0 +1,27 @@
+" Author: diartyz <diartyz@gmail.com>, w0rp <devw0rp@gmail.com>
+
+call ale#Set('less_stylelint_executable', 'stylelint')
+call ale#Set('less_stylelint_options', '')
+call ale#Set('less_stylelint_use_global', 0)
+
+function! ale_linters#less#stylelint#GetExecutable(buffer) abort
+    return ale#node#FindExecutable(a:buffer, 'less_stylelint', [
+    \   'node_modules/.bin/stylelint',
+    \])
+endfunction
+
+function! ale_linters#less#stylelint#GetCommand(buffer) abort
+    let l:executable = ale_linters#less#stylelint#GetExecutable(a:buffer)
+    let l:options = ale#Var(a:buffer, 'less_stylelint_options')
+
+    return ale#Escape(l:executable)
+    \   . (!empty(l:options) ? ' ' . l:options : '')
+    \   . ' --stdin-filename %s'
+endfunction
+
+call ale#linter#Define('less', {
+\   'name': 'stylelint',
+\   'executable_callback': 'ale_linters#less#stylelint#GetExecutable',
+\   'command_callback': 'ale_linters#less#stylelint#GetCommand',
+\   'callback': 'ale#handlers#css#HandleStyleLintFormat',
+\})