allow casks to support arbitrary blocks

this allows us to experiment with behavior that we may not want to
promote to an official feature just yet.

i'm thinking about stuff like Homebrew#544, and other things i can't foresee

we'll have to be careful to not let this get out of hand, but i think
it could be helpful for cask authors to be able to try and problem solve
locally.

lib/cask/artifact.rb

@@ -3,11 +3,12 @@ module Cask::Artifact; end
 require 'cask/artifact/base'
 
 require 'cask/artifact/app'
+require 'cask/artifact/block'
+require 'cask/artifact/font'
 require 'cask/artifact/nested_container'
 require 'cask/artifact/pkg'
 require 'cask/artifact/prefpane'
 require 'cask/artifact/qlplugin'
-require 'cask/artifact/font'
 
 module Cask::Artifact
   #
@@ -22,6 +23,7 @@ def self.artifacts
       Cask::Artifact::Prefpane,
       Cask::Artifact::Qlplugin,
       Cask::Artifact::Font,
+      Cask::Artifact::Block,
     ]
   end
 

lib/cask/artifact/block.rb

@@ -0,0 +1,15 @@
+class Cask::Artifact::Block < Cask::Artifact::Base
+  def self.me?(cask)
+    cask.artifacts[:after_install].any? ||
+      cask.artifacts[:after_uninstall].any?
+  end
+
+  def install
+    @cask.artifacts[:after_install].each { |block| block.call(@cask) }
+  end
+
+  def uninstall
+    @cask.artifacts[:after_uninstall].each { |block| block.call(@cask) }
+  end
+end
+

lib/cask/dsl.rb

@@ -51,6 +51,17 @@ def artifacts
       end
     end
 
+    ARTIFACT_BLOCK_TYPES = [
+      :after_install,
+      :after_uninstall
+    ]
+
+    ARTIFACT_BLOCK_TYPES.each do |type|
+      define_method(type) do |&block|
+        artifacts[type] << block
+      end
+    end
+
     attr_reader :sums
 
     def md5(md5=nil)

test/cask/artifact/block_test.rb

@@ -0,0 +1,45 @@
+require 'test_helper'
+
+describe Cask::Artifact::Block do
+  describe 'install' do
+    it 'calls the specified block after installing, passing the cask' do
+      called      = false
+      yielded_arg = nil
+
+      CaskWithAfterInstall = Class.new(Cask)
+      CaskWithAfterInstall.class_eval do
+        after_install do |c|
+          called = true
+          yielded_arg = c
+        end
+      end
+
+      cask = CaskWithAfterInstall.new
+      Cask::Artifact::Block.new(cask).install
+
+      called.must_equal true
+      yielded_arg.must_equal cask
+    end
+  end
+
+  describe 'uninstall' do
+    it 'calls the specified block after uninstalling, passing the cask' do
+      called      = false
+      yielded_arg = nil
+
+      CaskWithAfterUninstall = Class.new(Cask)
+      CaskWithAfterUninstall.class_eval do
+        after_uninstall do |c|
+          called = true
+          yielded_arg = c
+        end
+      end
+
+      cask = CaskWithAfterUninstall.new
+      Cask::Artifact::Block.new(cask).uninstall
+
+      called.must_equal true
+      yielded_arg.must_equal cask
+    end
+  end
+end