Add rake dev:cache task to enable development mode caching

[Sonopa]

Running rake dev:cache will create or remove tmp/caching-dev.txt. When this file exists config.action_controller.perform_caching will be set to true in config/environments/development.rb.

Fixes #18875.

[pixeltrix]

I'm 👍 on the idea of being able to easily toggle caching in development mode since more than once I've accidentally committed it after toggling it to true in development.rb whilst checking something. However I think this implementation isn't the right way to do this.

The two that readily spring to mind are:

1. CLI option: rails s --perform-caching=true
2. Environment variable: RAILS_PERFORM_CACHING=1 rails s

Wdyt @rafaelfranca @carlosantoniodasilva @jeremy ?

[rafaelfranca]

1 seems good to me.

[rafaelfranca]

cc @dhh since he created the original issue.

[carlosantoniodasilva]

👍. I think the original idea/pattern of using tmp/somefile.txt came from Basecamp, they are using that like feature toggles apparently. I'm not sure we're going to use that for any other thing right now, though, but the idea is that you don't need to manually restart the server.

I sort of like being able to do that from the rails server command, I'd not mind that being the only way for doing this. But lets see what else this pattern can be useful for first.

[dhh]

rails s --perform-caching=true only works when you're the one starting the server manually. That's not compatible with, say, Pow.

[magikid]

It looks like this issue has been merged in with PR #20961. Can this one be closed?