Free up #initialize for command subclasses

[timriley]

Free up #initialize in command subclasses so they can use it for their own purposes only.

stdin:, stdout:, and stderr: are still injectable dependencies, but these are handled by .new, which sets them as instance variables directly, before forwarding all other args onto #initialize.

Aside from reducing boilerplate for users in their command subclasses, this also decreases the risk of bugs. Without this, every command subclass that adds its own #initialize needs to remember to accept **args and then call super(**args), otherwise the streams would never be set.

I thought of this change as part of updating hanami-cli to use the new streams provided as part of dry-cli v2. Now that I've made this change here, my next step will be to show what the updated hanami-cli commands look like. Stand by for that, but in the meantime, I'm still interested in feedback on this change in isolation :)

[parndt]

I like this!

[aaronmallen]

This is good soup

[timriley]

Thanks for checking this out, folks! As it turns out, I discovered an additional need while continuing the hanami-cli updates: making it it possible for users of Dry CLI to specify their own "auto-assigned" keywords like we have here with stdout:, etc.

To support this, I've introduced an "auto-assigned keywords" feature. See it in the last commit above. The lowdown:

This feature formalises the behaviour we introduced where the stderr:, stdin:, stdout: args were assigned to ivars without subclass #initialize methods needing to worry about receiving those as **args and forwarding them to super.

Now our users can take advantage of this behavior. It’s common for a CLI app to require some “standard” dependencies be provided to every command class through their #initialize methods. These can now be set up like so:

# In a CLI app’s base command class

# `inflector:` is a standard dependency
def self.auto_assign_keywords = super + %i[inflector]

# Supply default values here
private def auto_assign(inflector: Dry::Inflector.new, **kwargs)
  super(**kwargs)
  @inflector = inflector
end

The above will make inflector: work as an argument to .new, and assign its value to an ivar automatically (via #auto_assign) before #initialize is called.

---

We're using this for the fs: dependency in hanami-cli. See lib/hanami/cli/command.rb in hanami/hanami-cli#447, where we do this:

def self.auto_assign_keywords = super + %i[fs]

# ...

private

def auto_assign(fs: nil, **kwargs)
  super(**kwargs)
  @fs = fs
end

This means we don't have to worry about adding **args and super(**args) to every single command subclass in Hanami CLI.

This is an example of Dry CLI working as "a framework for a framework", allowing CLI apps to implement their own common baseline behaviour without having to foist any boilerplate on their own internal command classes.

[alassek]

I have felt the awkwardness of this problem myself, and I think this is a reasonable approach.

[alassek]

Since this would be trivial enough to metaprogram auto_assign, is your intention here to make it difficult on purpose to discourage overuse?