Add stderr, stdin, and stdout support for Dry::CLI

Introduce `stderr`, `stdin`, and `stdout` streams to `Dry::CLI`
and its components to better handle I/O. This allows commands
to utilize specific input/output streams, improving flexibility
and testability. Refactor existing methods to use the new stream
parameters consistently.

Author: aaronmallen

lib/dry/cli.rb

@@ -57,12 +57,13 @@ def initialize(command_or_registry = nil, &block)
     # Invoke the CLI
     #
     # @param arguments [Array<string>] the command line arguments (defaults to `ARGV`)
-    # @param out [IO] the standard output (defaults to `$stdout`)
-    # @param err [IO] the error output (defaults to `$stderr`)
+    # @param stderr [IO] the error output (defaults to `$stderr`)
+    # @param stdin [IO] the standard input (defaults to `$stdin`)
+    # @param stdout [IO] the standard output (defaults to `$stdout`)
     #
     # @since 0.1.0
-    def call(arguments: ARGV, out: $stdout, err: $stderr)
-      @out, @err = out, err
+    def call(arguments: ARGV, stderr: $stderr, stdin: $stdin, stdout: $stdout)
+      @stderr, @stdin, @stdout = stderr, stdin, stdout
       kommand ? perform_command(arguments) : perform_registry(arguments)
     rescue SignalException => e
       signal_exception(e)
@@ -82,11 +83,15 @@ def call(arguments: ARGV, out: $stdout, err: $stderr)
 
     # @since 0.6.0
     # @api private
-    attr_reader :out
+    attr_reader :stderr
+
+    # @since unreleased
+    # @api private
+    attr_reader :stdin
 
     # @since 0.6.0
     # @api private
-    attr_reader :err
+    attr_reader :stdout
 
     # Invoke the CLI if singular command passed
     #
@@ -145,29 +150,29 @@ def parse(command, arguments, names)
     # @since 0.6.0
     # @api private
     def build_command(command)
-      command.is_a?(Class) ? command.new : command
+      command.is_a?(Class) ? command.new(stderr: stderr, stdin: stdin, stdout: stdout) : command
     end
 
     # @since 0.6.0
     # @api private
     def help(command, prog_name)
-      out.puts Banner.call(command, prog_name)
+      stdout.puts Banner.call(command, prog_name)
       exit(0) # Successful exit
     end
 
     # @since 0.6.0
     # @api private
     def error(result)
-      err.puts(result.error)
+      stderr.puts(result.error)
       exit(1)
     end
 
     # @since 1.1.1
     def spell_checker(result, arguments)
       spell_checker = SpellChecker.call(result, arguments)
-      err.puts spell_checker if spell_checker
+      stderr.puts spell_checker if spell_checker
       puts
-      err.puts Usage.call(result)
+      stderr.puts Usage.call(result)
       exit(1)
     end
 

lib/dry/cli/command.rb

@@ -366,6 +366,14 @@ def self.superclass_options
         superclass_variable_dup(:@options)
       end
 
+      # @since unreleased
+      # @api private
+      def initialize(stderr: $stderr, stdin: $stdin, stdout: $stdout)
+        @stderr = stderr
+        @stdin  = stdin
+        @stdout = stdout
+      end
+
       extend Forwardable
 
       delegate %i[
@@ -379,6 +387,52 @@ def self.superclass_options
         optional_arguments
         subcommands
       ] => "self.class"
+
+      protected
+
+      # The error output used to print error messaging
+      #
+      # @example
+      #   class MyCommand
+      #     def call
+      #       stdout.puts "Hello World!"
+      #       exit(0)
+      #     rescue StandardError => e
+      #       stderr.puts "Uh oh: #{e.message}"
+      #       exit(1)
+      #     end
+      #   end
+      #
+      # @since unreleased
+      # @return [IO]
+      attr_reader :stderr
+
+      # The standard input stream used for reading input
+      #
+      # @example
+      #   class MyCommand
+      #     def call
+      #       name = stdin.gets.chomp
+      #       stdout.puts "Hello #{name}!"
+      #     end
+      #   end
+      #
+      # @since unreleased
+      # @return [IO]
+      attr_reader :stdin
+
+      # The standard output stream used for normal output
+      #
+      # @example
+      #   class MyCommand
+      #     def call
+      #       stdout.puts "Hello World!"
+      #     end
+      #   end
+      #
+      # @since unreleased
+      # @return [IO]
+      attr_reader :stdout
     end
   end
 end

lib/dry/cli/inline.rb

@@ -60,13 +60,13 @@ module Inline
       #   end
       #
       # @since 0.6.0
-      def run(arguments: ARGV, out: $stdout)
+      def run(arguments: ARGV, stdout: $stdout)
         command = AnonymousCommand
         command.define_method(:call) do |**args|
           yield(**args)
         end
 
-        Dry.CLI(command).call(arguments: arguments, out: out)
+        Dry.CLI(command).call(arguments: arguments, stdout:)
       end
     end
   end