add Tap#install and Tap#uninstall

Library/Homebrew/cmd/tap.rb

 require "tap"
-require "descriptions"
 
 module Homebrew
   def tap
@@ -14,48 +13,22 @@ module Homebrew
       puts Tap.select(&:pinned?).map(&:name)
     else
       user, repo = tap_args
-      clone_target = ARGV.named[1]
-      opoo "#{user}/#{repo} already tapped!" unless install_tap(user, repo, clone_target)
+      tap = Tap.fetch(user, repo)
+      tap.install(:clone_target => ARGV.named[1], :full_clone => ARGV.include?("--full"))
     end
   end
 
+  # @deprecated this method will be removed in the future, if no external commands use it.
   def install_tap(user, repo, clone_target = nil)
-    # ensure git is installed
-    Utils.ensure_git_installed!
-
-    tap = Tap.fetch user, repo
-    return false if tap.installed?
-    ohai "Tapping #{tap}"
-    remote = clone_target || "https://github.com/#{tap.user}/homebrew-#{tap.repo}"
-    args = %W[clone #{remote} #{tap.path}]
-    args << "--depth=1" unless ARGV.include?("--full")
-
+    opoo "Homebrew.install_tap is deprecated, use Tap#install."
+    tap = Tap.fetch(user, repo)
     begin
-      safe_system "git", *args
-    rescue Interrupt, ErrorDuringExecution
-      ignore_interrupts do
-        sleep 0.1 # wait for git to cleanup the top directory when interrupt happens.
-        tap.path.parent.rmdir_if_possible
-      end
-      raise
-    end
-
-    formula_count = tap.formula_files.size
-    puts "Tapped #{formula_count} formula#{plural(formula_count, "e")} (#{tap.path.abv})"
-    Descriptions.cache_formulae(tap.formula_names)
-
-    if !clone_target && tap.private?
-      puts <<-EOS.undent
-        It looks like you tapped a private repository. To avoid entering your
-        credentials each time you update, you can use git HTTP credential
-        caching or issue the following command:
-
-          cd #{tap.path}
-          git remote set-url origin git@github.com:#{tap.user}/homebrew-#{tap.repo}.git
-      EOS
+      tap.install(:clone_target => clone_target, :full_clone => ARGV.include?("--full"))
+    rescue TapAlreadyTappedError
+      false
+    else
+      true
     end
-
-    true
   end
 
   # Migrate tapped formulae from symlink-based to directory-based structure.

Library/Homebrew/cmd/untap.rb

 require "cmd/tap" # for tap_args
-require "descriptions"
 
 module Homebrew
   def untap
@@ -7,17 +6,7 @@ module Homebrew
 
     ARGV.named.each do |tapname|
       tap = Tap.fetch(*tap_args(tapname))
-
-      raise TapUnavailableError, tap.name unless tap.installed?
-      puts "Untapping #{tap}... (#{tap.path.abv})"
-
-      tap.unpin if tap.pinned?
-
-      formula_count = tap.formula_files.size
-      Descriptions.uncache_formulae(tap.formula_names)
-      tap.path.rmtree
-      tap.path.dirname.rmdir_if_possible
-      puts "Untapped #{formula_count} formula#{plural(formula_count, "e")}"
+      tap.uninstall
     end
   end
 end

Library/Homebrew/tap.rb

 require "utils/json"
+require "descriptions"
 
 # a {Tap} is used to extend the formulae provided by Homebrew core.
 # Usually, it's synced with a remote git repository. And it's likely
@@ -89,6 +90,59 @@ class Tap
     @path.directory?
   end
 
+  # install this {Tap}.
+  #
+  # @param [Hash] options
+  # @option options [String]  :clone_targe If passed, it will be used as the clone remote.
+  # @option options [Boolean] :full_clone If set as true, full clone will be used.
+  def install(options = {})
+    raise TapAlreadyTappedError, name if installed?
+
+    # ensure git is installed
+    Utils.ensure_git_installed!
+    ohai "Tapping #{name}"
+    remote = options[:clone_target] || "https://github.com/#{@user}/homebrew-#{@repo}"
+    args = %W[clone #{remote} #{@path}]
+    args << "--depth=1" unless options.fetch(:full_clone, false)
+
+    begin
+      safe_system "git", *args
+    rescue Interrupt, ErrorDuringExecution
+      ignore_interrupts do
+        sleep 0.1 # wait for git to cleanup the top directory when interrupt happens.
+        @path.parent.rmdir_if_possible
+      end
+      raise
+    end
+
+    formula_count = formula_files.size
+    puts "Tapped #{formula_count} formula#{plural(formula_count, "e")} (#{@path.abv})"
+    Descriptions.cache_formulae(formula_names)
+
+    if !options[:clone_target] && private?
+      puts <<-EOS.undent
+        It looks like you tapped a private repository. To avoid entering your
+        credentials each time you update, you can use git HTTP credential
+        caching or issue the following command:
+          cd #{@path}
+          git remote set-url origin git@github.com:#{@user}/homebrew-#{@repo}.git
+      EOS
+    end
+  end
+
+  # uninstall this {Tap}.
+  def uninstall
+    raise TapUnavailableError, name unless installed?
+
+    puts "Untapping #{name}... (#{@path.abv})"
+    unpin if pinned?
+    formula_count = formula_files.size
+    Descriptions.uncache_formulae(formula_names)
+    @path.rmtree
+    @path.dirname.rmdir_if_possible
+    puts "Untapped #{formula_count} formula#{plural(formula_count, "e")}"
+  end
+
   # True if the {#remote} of {Tap} is customized.
   def custom_remote?
     return true unless remote