DSL: add conflicts_with stanza

Forgotten in Homebrew#4688, but should be considered part of Cask DSL 1.0.
A `depends_on` stanza is much less useful without the corresponding
`conflicts_with`.

References: Homebrew#4896

lib/cask.rb

@@ -16,6 +16,7 @@ class Cask; end
 require 'cask/checkable'
 require 'cask/cli'
 require 'cask/caveats'
+require 'cask/conflicts_with'
 require 'cask/container'
 require 'cask/depends_on'
 require 'cask/download'

lib/cask/conflicts_with.rb

@@ -0,0 +1,31 @@
+class Cask::ConflictsWith
+
+  VALID_KEYS = Set.new [
+                        :formula,
+                        :cask,
+                        :macos,
+                        :arch,
+                        :x11,
+                        :java,
+                       ]
+
+  attr_accessor *VALID_KEYS
+  attr_accessor :pairs
+
+  def initialize(pairs={})
+    @pairs = pairs
+    pairs.each do |key, value|
+      raise "invalid conflicts_with key: '#{key.inspect}'" unless VALID_KEYS.include?(key)
+      writer_method = "#{key}=".to_sym
+      send(writer_method, value)
+    end
+  end
+
+  def to_yaml
+    @pairs.to_yaml
+  end
+
+  def to_s
+    @pairs.inspect
+  end
+end

lib/cask/dsl.rb

@@ -22,6 +22,8 @@ def depends_on_formula; self.class.depends_on_formula; end
 
   def depends_on; self.class.depends_on; end
 
+  def conflicts_with; self.class.conflicts_with; end
+
   def container_type; self.class.container_type; end
 
   def tags; self.class.tags; end
@@ -137,6 +139,18 @@ def depends_on(*args)
       @depends_on
     end
 
+    def conflicts_with(*args)
+      if @conflicts_with and !args.empty?
+        # todo: remove this constraint, and instead merge multiple conflicts_with stanzas
+        raise CaskInvalidError.new(self.title, "'conflicts_with' stanza may only appear once")
+      end
+      @conflicts_with ||= begin
+        Cask::ConflictsWith.new(*args) unless args.empty?
+      rescue StandardError => e
+        raise CaskInvalidError.new(self.title, e)
+      end
+    end
+
     def artifacts
       @artifacts ||= Hash.new { |hash, key| hash[key] = Set.new }
     end

lib/cask/utils.rb

@@ -83,6 +83,7 @@ def dumpcask
        :artifacts,
        :caveats,
        :depends_on_formula,
+       :conflicts_with,
        :container_type,
        :gpg,
       ].each do |method|

test/cask/dsl_test.rb

@@ -198,6 +198,19 @@ def caveats; <<-EOS.undent
     end
   end
 
+  describe "conflicts_with stanza" do
+    it "allows conflicts_with stanza to be specified" do
+      cask = Cask.load('with-conflicts-with')
+      cask.conflicts_with.formula.wont_be_nil
+    end
+
+    it "refuses to load invalid conflicts_with key" do
+      err = lambda {
+        invalid_cask = Cask.load('invalid/invalid-conflicts-with-key')
+      }.must_raise(CaskInvalidError)
+    end
+  end
+
   describe "license stanza" do
     it "allows the license to be specified" do
       cask = Cask.load('with-license')

test/support/Casks/invalid/invalid-conflicts-with-key.rb

@@ -0,0 +1,8 @@
+class InvalidConflictsWithKey < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/invalid-conflicts-with-key'
+  conflicts_with :no_such_key => 'unar'
+  sha256 '9203c30951f9aab41ac294bbeb1dcef7bed401ff0b353dcb34d68af32ea51853'
+  version '1.2.3'
+  link 'Caffeine.app'
+end

test/support/Casks/with-conflicts-with.rb

@@ -0,0 +1,8 @@
+class WithConflictsWith < TestCask
+  url TestHelper.local_binary('caffeine.zip')
+  homepage 'http://example.com/with-conflicts-with'
+  conflicts_with :formula => 'unar'
+  sha256 '9203c30951f9aab41ac294bbeb1dcef7bed401ff0b353dcb34d68af32ea51853'
+  version '1.2.3'
+  link 'Caffeine.app'
+end