If you google around for ycm_extra_conf.py you’ll find more usages, and some people hinting at the location. this page mentions it is placed in your homedir. Oh, and here are the You Complete Me docs that mention the config file and how/where YCM looks for it.
I’ve replied to you linting question on github. Shouldn’t be difficult, but a quick search on ALE config options/flags/variables gave me nothing.
Thanks for the help. I started working on ale-platformio.vim and it seems to work ok. One thing I did notice is that findfile("platformio.ini", ".;") doesn’t work if you start vim in a directory.