Allow categories: true to make feeds for all categories

[jez]

Motivation

Fixes #361

Summary

This change behaves like how tags: true works, and like how @parkr suggested
in the comments of #361.

If there's anything you'd like changed in the implementation, please let me know.

Test plan

I've written a test case for this and also verified that it works for my
personal blog when I pass categories: true in my feed: settings.

[jez]

(This is based on the fixed master commit now)

[jez]

Sorry about that, I didn’t realize that rubocop was set up for the repo, and I had forgotten to run that locally.

I fixed the rubocop errors by factoring out my changes to a new method. Feel free to suggest any tweaks as you wish.

[ashmaroli]

Hello @jez, you needn't apologize for overlooking RuboCop offenses. It's part of the process.

Anyways, I'm finding the use of param name meta confusing now that the logic has been abstracted to a separate definition.
How about using collection itself

Edit: I read the code wrong.

[jez]

@ashmaroli I saw you crossed out your request–is there anything else you'd like me to change about this PR?

(otherwise, I think this change is ready to go)

[jez]

@ashmaroli friendly bump!

[ashmaroli]

Thanks for the ping, @jez. This had fallen off my radar.

[ashmaroli]

LGTM!

[parkr]

On line 24 of generator.rb, we have special handling for config["tags"]. Do we intend to only generate collection-level categories?

[parkr]

We might want to explain that in the current implementation, this means that each collection will get its own category feed. This operates differently than tag-based feeds where they unify all documents from any collection into a single feed.

[parkr]

Can we have a test for this? It seems like we could over-generate. That is we could generate a category feed which has zero entries since a collection doesn't have any documents with a category that is only present in another collection.

1. Collection "posts" has categories "A" and "B"
2. Collection "archives" has categories "C"
3. Will we generate /feed/archives/A.xml with zero entries?

Concerns raised by co-maintainer needs to be addressed