Consider the following configuration:

version: "2"
plugins:
  eslint:
    enabled: true
    channel: "eslint-4"
    config:
      config: ./.eslintrc.js
      extensions:
        - .js

This is correct, and uses ESLint 4.

version: "2"
plugins:
  eslint:
    enabled: true
    config:
      config: ./.eslintrc.js
      channel: "eslint-4"
      extensions:
        - .js

This is incorrect, but no warnings are given by codeclimate analyze -e eslint when this configuration is used. If I use the incorrect configuration, I see:

16:54 $ CODECLIMATE_DEBUG=1 codeclimate analyze -e eslint /path/to/file.js
Starting analysis
I, [2018-03-12T20:55:14.545541 #1]  INFO -- : starting engine eslint
D, [2018-03-12T20:55:14.566194 #1] DEBUG -- : /config.json content: {"enabled"=>true, "config"=>{"config"=>"./.eslintrc.js", "channel"=>"eslint-4", "extensions"=>[".js"]}, "channel"=>"stable", "include_paths"=>["/path/to/file.js"], "debug"=>"1"}
D, [2018-03-12T20:55:14.582168 #1] DEBUG -- : docker run: ["docker", "run", "--name", "cc-engines-eslint-stable-6e3962ef-06db-4b4f-8488-f505dbe10c5b", "--cap-drop", "all", "--label", "com.codeclimate.label=24bcce10-3cf7-4329-8c0f-ce9f5f86b5a4", "--log-driver", "none", "--memory", "1024000000", "--memory-swap", "-1", "--net", "none", "--rm", "--volume", "/Users/kostajh/src/project:/code:ro", "--volume", "/tmp/cc/a686e6d6-d32b-4ab7-b1b4-568d1852f8e2:/config.json:ro", "--user", "9000:9000", "codeclimate/codeclimate-eslint"]
D, [2018-03-12T20:55:15.421642 #1] DEBUG -- : engine stderr: ESLint is running with the default parser.
D, [2018-03-12T20:55:15.439805 #1] DEBUG -- : engine stderr:
I, [2018-03-12T20:55:16.000033 #1]  INFO -- : finished engine eslint

From a superficial view, it appears that eslint-4 is used but in fact it's not. To debug, I had to construct a docker run command from the output above, then look at the Dockerfile entrypoint.sh file, then see that eslint was on version 3.

Using the correct config, the only visible difference is that codeclimate/codeclimate-eslint:eslint-4 is now used as the image; now that I know to look for this, it's obvious, but before it wasn't.

Anyway, in short, it would be helpful to warn users about invalid config options to save time on debugging. Thanks for considering!