Chore: Adding debug logs on successful plugin loads

[platinumazure]

What is the purpose of this pull request? (put an "X" next to item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[x] Other, please explain: Adding some debug logs for successful plugin loads, to help users detect if plugin versions don't match expectations.

What changes did you make? (Give an overview)

Added some debug logging to lib/config/plugins.js on successful plugin load. These statements note the plugin name (as specified in config), the resolved plugin name, and the version of the loaded plugin (if we can determine it).

This logic is only executed if debug is actually enabled. This is because the most reliable way I know of for finding a plugin version is to require the package.json file within the plugin package and read the version property. There's no point in resolving, loading, and reading that file if debug isn't enabled, hence the extra if check.

Is there anything you'd like reviewers to focus on?

• Is there a better way for me to read a package version?
• Should I add any unit tests for this change? If so, any tips for getting started?
• Anything else I should consider adding to the debug statements? Is there a better way to present the information?

Example output when running DEBUG=eslint:plugins node ./bin/eslint.js lib (from root of ESLint project):

2018-03-19T18:00:03.314Z eslint:plugins Loaded plugin eslint-plugin (eslint-plugin-eslint-plugin@1.2.0)
2018-03-19T18:00:03.365Z eslint:plugins Loaded plugin node (eslint-plugin-node@5.1.0)
2018-03-19T18:00:03.366Z eslint:plugins Loaded plugin rulesdir (eslint-plugin-rulesdir@0.1.0)

(Note: Looks a bit different than when run on console due to output redirect. Just ignore the timestamps.)

---

Inspired by #10090. This output could be useful for users who expect a certain plugin version to be loaded, but they get a different version due to either global/local mismatching or npm/yarn shenanigans.

[not-an-aardvark]

LGTM. Should we also include the absolute path of the plugin?

[platinumazure]

@not-an-aardvark Good call, I've added the resolved path.

Here's how the output looks now:

2018-03-19T21:34:56.627Z eslint:plugins Loaded plugin eslint-plugin (eslint-plugin-eslint-plugin@1.2.0) (from C:\Users\kpartington\Documents\GitHub\eslint\node_modules\eslint-plugin-eslint-plugin\lib\index.js)
2018-03-19T21:34:56.679Z eslint:plugins Loaded plugin node (eslint-plugin-node@5.1.0) (from C:\Users\kpartington\Documents\GitHub\eslint\node_modules\eslint-plugin-node\lib\index.js)
2018-03-19T21:34:56.680Z eslint:plugins Loaded plugin rulesdir (eslint-plugin-rulesdir@0.1.0) (from C:\Users\kpartington\Documents\GitHub\eslint\node_modules\eslint-plugin-rulesdir\index.js)