cmd/uninstall: Add env variable that runs autoremove after uninstalls

When HOMEBREW_UNINSTALL_AUTOREMOVE is set, `brew autoremove` is run
after every successful call to `brew uninstall`.

Library/Homebrew/cmd/uninstall.rb

@@ -50,6 +50,11 @@ module Homebrew
       all_kegs:           args.force?,
     )
 
+    # If ignore_unavailable is true and the named args
+    # are a series of invalid kegs and casks,
+    # #to_kegs_to_casks will return empty arrays.
+    return if all_kegs.blank? && casks.blank?
+
     kegs_by_rack = all_kegs.group_by(&:rack)
 
     Uninstall.uninstall_kegs(
@@ -73,5 +78,9 @@ module Homebrew
         force:   args.force?,
       )
     end
+
+    return unless Homebrew::EnvConfig.uninstall_autoremove?
+
+    system HOMEBREW_BREW_FILE, "autoremove"
   end
 end

Library/Homebrew/env_config.rb

@@ -343,6 +343,10 @@ module Homebrew
         default_text: "macOS: `/private/tmp`, Linux: `/tmp`.",
         default:      HOMEBREW_DEFAULT_TEMP,
       },
+      HOMEBREW_UNINSTALL_AUTOREMOVE:             {
+        description: "If set, `brew autoremove` is run after every successful call to `brew uninstall`.",
+        boolean:     true,
+      },
       HOMEBREW_UPDATE_REPORT_ALL_FORMULAE:       {
         description: "If set, `brew update` lists changes to all formulae and cask files rather than only showing " \
                      "when they are new and not installed or outdated and installed.",

Library/Homebrew/sorbet/rbi/hidden-definitions/hidden.rbi

@@ -2572,6 +2572,8 @@ module Homebrew::EnvConfig
 
   def self.temp(); end
 
+  def self.uninstall_autoremove?(); end
+
   def self.update_report_all_formulae?(); end
 
   def self.update_to_tag?(); end

docs/Manpage.md

@@ -2184,6 +2184,9 @@ example, run `export HOMEBREW_NO_INSECURE_REDIRECT=1` rather than just
 
   *Default:* macOS: `/private/tmp`, Linux: `/tmp`.
 
+- `HOMEBREW_UNINSTALL_AUTOREMOVE`
+  <br>If set, `brew autoremove` is run after every successful call to `brew uninstall`.
+
 - `HOMEBREW_UPDATE_REPORT_ALL_FORMULAE`
   <br>If set, `brew update` lists changes to all formulae and cask files rather than only showing when they are new and not installed or outdated and installed.
 

manpages/brew.1

@@ -3207,6 +3207,12 @@ Use this path as the temporary directory for building packages\. Changing this m
 \fIDefault:\fR macOS: \fB/private/tmp\fR, Linux: \fB/tmp\fR\.
 .
 .TP
+\fBHOMEBREW_UNINSTALL_AUTOREMOVE\fR
+.
+.br
+If set, \fBbrew autoremove\fR is run after every successful call to \fBbrew uninstall\fR\.
+.
+.TP
 \fBHOMEBREW_UPDATE_REPORT_ALL_FORMULAE\fR
 .
 .br