Add a luac linter for Lua

ale_linters/lua/luac.vim

@@ -0,0 +1,40 @@
+" Author: Jon Xie https://github.com/xiejiangzhi
+" Description: luac linter for lua files
+
+call ale#Set('lua_luac_executable', 'luac')
+
+function! ale_linters#lua#luac#GetExecutable(buffer) abort
+    return ale#Var(a:buffer, 'lua_luac_executable')
+endfunction
+
+function! ale_linters#lua#luac#GetCommand(buffer) abort
+    let l:executable = ale_linters#lua#luac#GetExecutable(a:buffer)
+    return ale#Escape(l:executable) . ' -p - '
+endfunction
+
+function! ale_linters#lua#luac#Handle(buffer, lines) abort
+    " Matches patterns line the following:
+    "
+    " luac: stdin:5: '=' expected near ')'
+    " luac: stdin:8: ')' expected (to close '(' at line 6) near '123'
+    let l:pattern = '\v^.*:(\d+): (.+)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        call add(l:output, {
+        \   'lnum': l:match[1] + 0,
+        \   'type': 'E',
+        \   'text': l:match[2],
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('lua', {
+\   'name': 'luac',
+\   'executable_callback': 'ale_linters#lua#luac#GetExecutable',
+\   'command_callback': 'ale_linters#lua#luac#GetCommand',
+\   'output_stream': 'stderr',
+\   'callback': 'ale_linters#lua#luac#Handle',
+\})