enforce a valid minimum DSL version in headers

lib/cask/source/path_base.rb

@@ -45,12 +45,17 @@ def load
       # munge text
       cask_string.sub!(%r{\A(\s*\#[^\n]*\n)+}, '');
       if %r{\A\s*cask\s+:v([\d_]+)(test)?\s+=>\s+([\'\"])(\S+?)\3(?:\s*,\s*|\s+)do\s*\n}.match(cask_string)
-        dsl_version = $1
+        dsl_version_string = $1
         test_cask = ! $2.nil?
         header_name = $4
+        dsl_version = Gem::Version.new(dsl_version_string.gsub('_','.'))
         superclass_name = test_cask ? 'TestCask' : 'Cask'
         cask_string.sub!(%r{\A[^\n]+\n}, "class #{cask_class_name} < #{superclass_name}\n")
-        # todo enforce valid DSL version
+        # todo the minimum DSL version should be defined globally elsewhere
+        minimum_dsl_version = Gem::Version.new('1.0')
+        unless dsl_version >= minimum_dsl_version
+          raise CaskInvalidError.new(cask_name, "Bad header line: 'v#{dsl_version_string}' is less than required minimum version '#{minimum_dsl_version}'")
+        end
         if header_name != cask_name
           raise CaskInvalidError.new(cask_name, "Bad header line: '#{header_name}' does not match file name")
         end

test/cask/dsl_test.rb

@@ -32,6 +32,16 @@
     end
   end
 
+  describe "header line" do
+    it "requires a valid minimum DSL version in the header" do
+      err = lambda {
+        invalid_cask = Cask.load('invalid/invalid-header-version')
+      }.must_raise(CaskInvalidError)
+      err.message.must_include 'Bad header line'
+      err.message.must_include 'is less than required minimum version'
+    end
+  end
+
   describe "sha256 stanza" do
     it "lets you set checksum via sha256" do
       ChecksumCask = Class.new(Cask)

test/support/Casks/invalid/invalid-header-version.rb

@@ -0,0 +1,9 @@
+cask :v0_9test => 'invalid-header-version' do
+  version '1.2.3'
+  sha256 '9203c30951f9aab41ac294bbeb1dcef7bed401ff0b353dcb34d68af32ea51853'
+
+  url TestHelper.local_binary_url('caffeine.zip')
+  homepage 'http://example.com/local-caffeine'
+
+  app 'Caffeine.app'
+end