support for caveats

i.e. custom messages printed after installing a cask

refs Homebrew#218

Casks/adobe-air.rb

@@ -2,10 +2,12 @@ class AdobeAir < Cask
   url 'http://airdownload.adobe.com/air/mac/download/3.5/AdobeAIR.dmg'
   homepage 'https://get.adobe.com/air/'
   version '3.5'
-
-  #caveat 'You need to run {{install_path}}/AdobeAIRInstaller.app to actually install Adobe AIR'
-
   sha1 '8fbd2dffc20442903d8b51e7362a3191f39752b4'
 
   link :app, :none
+
+  def caveats; <<-EOS.undent
+    You need to run #{destination_path/'AdobeAIRInstaller.app'} to actually install Adobe AIR
+    EOS
+  end
 end

lib/cask/dsl.rb

@@ -16,6 +16,8 @@ def sums; self.class.sums || []; end
 
   def linkables; self.class.linkables || {}; end
 
+  def caveats; ''; end
+
   module ClassMethods
     def homepage(homepage=nil)
       @homepage ||= homepage

lib/cask/installer.rb

@@ -17,6 +17,10 @@ def install(cask)
       end
 
       ohai "Success! #{cask} installed to #{cask.destination_path}"
+
+      unless cask.caveats.empty?
+        ohai 'Caveats', cask.caveats
+      end
     end
 
     def uninstall(cask)

test/cask/dsl_test.rb

@@ -69,4 +69,24 @@
     instance = CaskWithNoLinkables.new
     Array(instance.linkable_apps).must_equal %w[]
   end
+
+  it "allows caveats to be specified via a method define" do
+    PlainCask = Class.new(Cask)
+
+    instance = PlainCask.new
+
+    instance.caveats.must_be :empty?
+
+    CaskWithCaveats = Class.new(Cask)
+    CaskWithCaveats.class_eval do
+      def caveats; <<-EOS.undent
+        When you install this cask, you probably want to know this.
+        EOS
+      end
+    end
+
+    instance = CaskWithCaveats.new
+
+    instance.caveats.must_equal "When you install this cask, you probably want to know this.\n"
+  end
 end

test/cask/installer_test.rb

@@ -53,6 +53,14 @@
       end
       no_checksum.must_be :installed?
     end
+
+    it "prints caveats if they're present" do
+      with_caveats = Cask.load('with-caveats')
+      TestHelper.must_output(self, lambda {
+        Cask::Installer.install(with_caveats)
+      }, /Here are some things you might want to know/)
+      with_caveats.must_be :installed?
+    end
   end
 
   describe "uninstall" do

test/support/Casks/with-caveats.rb

@@ -0,0 +1,11 @@
+class WithCaveats < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+  version '1.2.3'
+  sha1 'd2fbdad1619934313026fc831e6c6e3dd97ac030'
+
+  def caveats; <<-EOS.undent
+    Here are some things you might want to know.
+    EOS
+  end
+end

test/test_helper.rb

@@ -58,7 +58,11 @@ def self.must_output(test, lambda, expected)
       lambda.call
     end
 
-    (out+err).chomp.must_equal expected.gsub(/^ */, '')
+    if expected.is_a? Regexp
+      (out+err).chomp.must_match expected
+    else
+      (out+err).chomp.must_equal expected.gsub(/^ */, '')
+    end
   end
 
   def self.valid_alias?(candidate)