cmd: add autoremove command

Library/Homebrew/cmd/autoremove.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "formula"
+require "cli/parser"
+
+module Homebrew
+  module_function
+
+  def autoremove_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `autoremove` [<options>]
+
+        Remove packages that weren't installed on request and are no longer needed.
+      EOS
+      switch "-n", "--dry-run",
+             description: "Just print what would be removed."
+      named 0
+    end
+  end
+
+  def get_removable_formulae(installed_formulae)
+    removable_formulae = []
+
+    installed_formulae.each do |formula|
+      # Reject formulae installed on request.
+      next if Tab.for_keg(formula.any_installed_keg).installed_on_request
+      # Reject formulae which are needed at runtime by other formulae.
+      next if installed_formulae.flat_map(&:runtime_formula_dependencies).include?(formula)
+
+      removable_formulae << installed_formulae.delete(formula)
+      removable_formulae += get_removable_formulae(installed_formulae)
+    end
+
+    removable_formulae
+  end
+
+  def autoremove
+    args = autoremove_args.parse
+
+    removable_formulae = get_removable_formulae(Formula.installed.sort)
+
+    return if removable_formulae.blank?
+
+    formulae_names = removable_formulae.map(&:full_name)
+
+    oh1 "Formulae that could be removed"
+    puts formulae_names
+
+    return if args.dry_run?
+
+    system HOMEBREW_BREW_FILE, "rm", *formulae_names
+  end
+end

Library/Homebrew/test/.rubocop_todo.yml

@@ -33,6 +33,7 @@ RSpec/MultipleDescribes:
     - 'cmd/--repository_spec.rb'
     - 'cmd/--version_spec.rb'
     - 'cmd/analytics_spec.rb'
+    - 'cmd/autoremove_spec.rb'
     - 'cmd/cleanup_spec.rb'
     - 'cmd/commands_spec.rb'
     - 'cmd/config_spec.rb'

Library/Homebrew/test/cmd/autoremove_spec.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require "cmd/shared_examples/args_parse"
+
+describe "Homebrew.autoremove_args" do
+  it_behaves_like "parseable arguments"
+end

completions/internal_commands_list.txt

@@ -12,6 +12,7 @@
 abv
 analytics
 audit
+autoremove
 bottle
 bump
 bump-cask-pr

docs/Manpage.md

@@ -56,6 +56,13 @@ Turn Homebrew's analytics on or off respectively.
 `brew analytics regenerate-uuid`:
 Regenerate the UUID used for Homebrew's analytics.
 
+### `autoremove` [*`options`*]
+
+Remove packages that weren't installed on request and are no longer needed.
+
+* `-n`, `--dry-run`:
+  Just print what would be removed.
+
 ### `cask` *`command`* [*`options`*] [*`cask`*]
 
 Homebrew Cask provides a friendly CLI workflow for the administration of macOS applications distributed as binaries.

manpages/brew.1

@@ -53,6 +53,13 @@ Control Homebrew\'s anonymous aggregate user behaviour analytics\. Read more at
 \fBbrew analytics regenerate\-uuid\fR
     Regenerate the UUID used for Homebrew\'s analytics\.
 .
+.SS "\fBautoremove\fR [\fIoptions\fR]"
+Remove packages that weren\'t installed on request and are no longer needed\.
+.
+.TP
+\fB\-n\fR, \fB\-\-dry\-run\fR
+Just print what would be removed\.
+.
 .SS "\fBcask\fR \fIcommand\fR [\fIoptions\fR] [\fIcask\fR]"
 Homebrew Cask provides a friendly CLI workflow for the administration of macOS applications distributed as binaries\.
 .