untap: add --force switch

Co-authored-by: Eric Knibbe <enk3@outlook.com>

Library/Homebrew/cmd/untap.rb

@@ -28,6 +28,24 @@ module Homebrew
       tap = Tap.fetch(tapname)
       odie "Untapping #{tap} is not allowed" if tap.core_tap?
 
+      installed_tap_formulae = Formula.installed.select { |formula| formula.tap == tap }
+      installed_tap_casks = Cask::Caskroom.casks.select { |cask| cask.tap == tap }
+
+      if installed_tap_formulae.present? || installed_tap_casks.present?
+        installed_names = (installed_tap_formulae + installed_tap_casks.map(&:token)).join("\n")
+        if args.force? || Homebrew::EnvConfig.developer?
+          opoo <<~EOS
+            Untapping #{tap} even though it contains the following installed formulae or casks:
+            #{installed_names}
+          EOS
+        else
+          odie <<~EOS
+            Refusing to untap #{tap} because it contains the following installed formulae or casks:
+            #{installed_names}
+          EOS
+        end
+      end
+
       tap.uninstall
     end
   end