Add --installed-(on-request/as-dependency) flags

Library/Homebrew/cmd/leaves.rb

@@ -15,14 +15,40 @@ module Homebrew
       description <<~EOS
         List installed formulae that are not dependencies of another installed formula.
       EOS
+      switch "-r", "--installed-on-request",
+             description: "Only list leaves that were manually installed."
+      switch "-p", "--installed-as-dependency",
+             description: "Only list leaves that were installed as dependencies."
 
       named_args :none
     end
   end
 
-  def leaves
-    leaves_args.parse
+  def installed_on_request?(leaf)
+    Tab.for_keg(leaf.any_installed_keg).installed_on_request
+  end
 
-    Formula.installed_formulae_with_no_dependents.map(&:full_name).sort.each(&method(:puts))
+  def installed_as_dependency?(leaf)
+    Tab.for_keg(leaf.any_installed_keg).installed_as_dependency
+  end
+
+  def leaves
+    args = leaves_args.parse
+
+    leaves_list = Formula.installed_formulae_with_no_dependents
+
+    if args.installed_on_request?
+      leaves_list.select! do |l|
+        installed_on_request?(l)
+      end
+    end
+
+    if args.installed_as_dependency?
+      leaves_list.select! do |l|
+        installed_as_dependency?(l)
+      end
+    end
+
+    leaves_list.map(&:full_name).sort.each(&method(:puts))
   end
 end