Add `Cached` module to simplify caching code.

[reitermarkus]

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---

Also added a separate version of Cachable#cache which takes a block and automatically freezes the cached value.

[apainintheneck]

I'm not sure that it's intuitive to include and extend the same module in different places in the codebase especially if we're planning on doing both in the same class. It might be worth thinking up some way of differentiating the instance cache from the class/module cache.

Interestingly enough we do have this pattern in a few places in the codebase but it's never truly an instance cache.

$ cd $(brew --repo)
$ git grep --no-index -C 4 'include Cachable'
Library/Homebrew/api/cask.rb-    #
Library/Homebrew/api/cask.rb-    # @api private
Library/Homebrew/api/cask.rb-    module Cask
Library/Homebrew/api/cask.rb-      class << self
Library/Homebrew/api/cask.rb:        include Cachable
Library/Homebrew/api/cask.rb-
Library/Homebrew/api/cask.rb-        private :cache
Library/Homebrew/api/cask.rb-
Library/Homebrew/api/cask.rb-        sig { params(token: String).returns(Hash) }
--
Library/Homebrew/api/formula.rb-    #
Library/Homebrew/api/formula.rb-    # @api private
Library/Homebrew/api/formula.rb-    module Formula
Library/Homebrew/api/formula.rb-      class << self
Library/Homebrew/api/formula.rb:        include Cachable
Library/Homebrew/api/formula.rb-
Library/Homebrew/api/formula.rb-        private :cache
Library/Homebrew/api/formula.rb-
Library/Homebrew/api/formula.rb-        sig { params(name: String).returns(Hash) }
--
Library/Homebrew/readall.rb-#
Library/Homebrew/readall.rb-# @api private
Library/Homebrew/readall.rb-module Readall
Library/Homebrew/readall.rb-  class << self
Library/Homebrew/readall.rb:    include Cachable
Library/Homebrew/readall.rb-    include SystemCommand::Mixin
Library/Homebrew/readall.rb-
Library/Homebrew/readall.rb-    # TODO: remove this once the `MacOS` module is undefined on Linux
Library/Homebrew/readall.rb-    MACOS_MODULE_REGEX = /\b(MacOS|OS::Mac)(\.|::)\b/

[reitermarkus]

not sure that it's intuitive to include and extend the same module

I disagree, that's just how Ruby works, but it is actually quite surprising that all existing usages so far are class-level caches.

[apainintheneck]

not sure that it's intuitive to include and extend the same module

I disagree, that's just how Ruby works, but it is actually quite surprising that all existing usages so far are class-level caches.

Fair enough. Maybe I'm overthinking this.

[apainintheneck]

There are a few places in the code that use cache.fetch(:key) { logic } and those can probably be cleaned up after this change too.

[reitermarkus]

restrict this to methods without arguments with method.arity.zero?

I tried this in the beginning, but that actually only works when not using Sorbet at runtime because Sorbet will always wrap all methods with *args.

[apainintheneck]

restrict this to methods without arguments with method.arity.zero?

I tried this in the beginning, but that actually only works when not using Sorbet at runtime because Sorbet will always wrap all methods with *args.

Lovely... it sometimes feels like I'm fighting Sorbet when I propose generic solutions.

[apainintheneck]

I'll throw another tangentially related idea out there. Maybe it'd be good to somehow programmatically collect all classes and modules that mix in Cachable and then clear those caches in-between tests. That would make it harder to forget to clear the cache of some module. This probably doesn't need to happen at the instance level though. To be clear, I'm not suggesting that this should be included in this PR. I'm just thinking out loud.

[github-actions[bot]]

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[MikeMcQuaid]

Passing on this, sorry.