(4 of 4) Allow explicit dependencies injected into Command with dry-auto_inject (if accepted, stacks on top of #174)

[kigster]

Proposal 4 of 4 in the dry-cli plugin-hooks series. It should be stacked on #175, but I don't have permission to set the base to a branch on a fork, it seems. Upstream issue/forum thread: pending.

Why

It's pretty common from what I've seen, and useful, to be able to define your custom BaseCommand (typically abstract), that decorates all of the inheriting commands with a specific behavior. One of such cases is to set a ui object and make it available throughout command lifecycle, to show errors in boxes, progress bars and concurrenly updating multiple spinners, and so on.

Other examples include injecting a database or Redis client driver.

Who uses it

Among my gems:

• dry-cli-help and
• dry-cli-ui

Summary

No library code changes. Shared per-command objects are dry-rb's job already: commands work with dry-auto_inject (and so dry-system containers) through Command.new. This PR documents it on Command and pins it with specs.

Deps = Dry::AutoInject(MyApp::Container)

class BaseCommand < Dry::CLI::Command
  include Deps["logger", "config"]
end

class Deploy < BaseCommand
  def initialize(target: "production", **)
    super(**)            # required, as for any class using dry-auto_inject
    @target = target
  end
end

Objects built from a command's streams can't come from a container. The docs give the rule for memoizing them, since an instance command is reused across calls (and across tests with Launcher):

def logger
  @logger = nil unless @logger_stream.equal?(stdout)
  @logger_stream = stdout
  @logger ||= Logger.new(stdout)
end

Evidence

• Before: undocumented; a subclass #initialize without super(**) fails with ArgumentError: unknown keyword: :clock, with no guidance.

• After: spec/integration/auto_inject_spec.rb (6): base-command injection, streams set before #initialize, instance commands, explicit keyword overriding the container, own #initialize with super(**), and the documented failure without it. The stream-memoization rule is exercised in launcher_spec.rb (Basic commands #1). Full suite 687 examples, 0 failures; rubocop clean; no new undocumented YARD objects.

Merge Danger

Docs and specs only; dry-auto_inject is a new development-only dependency.