cask audit: check for :latest with appcast

Library/Homebrew/cask/lib/hbc/audit.rb

@@ -35,6 +35,7 @@ module Hbc
       check_single_uninstall_zap
       check_untrusted_pkg
       check_github_releases_appcast
+      check_latest_with_appcast
       self
     rescue StandardError => e
       odebug "#{e.message}\n#{e.backtrace.join("\n")}"
@@ -228,6 +229,13 @@ module Hbc
       end
     end
 
+    def check_latest_with_appcast
+      return unless cask.version.latest?
+      return unless cask.appcast
+
+      add_warning "Casks with an appcast should not use version :latest"
+    end
+
     def check_github_releases_appcast
       return if cask.appcast
       return unless cask.url.to_s =~ %r{github.com/([^/]+)/([^/]+)/releases/download/(\S+)}

Library/Homebrew/test/cask/audit_spec.rb

@@ -387,6 +387,25 @@ describe Hbc::Audit, :cask do
       end
     end
 
+    describe "latest with appcast checks" do
+      let(:error_msg) { "Casks with an appcast should not use version :latest" }
+
+      context "when the Cask is :latest and does not have an appcast" do
+        let(:cask_token) { "version-latest" }
+        it { should_not warn_with(error_msg) }
+      end
+
+      context "when the Cask is versioned and has an appcast" do
+        let(:cask_token) { "with-appcast" }
+        it { should_not warn_with(error_msg) }
+      end
+
+      context "when the Cask is :latest and has an appcast" do
+        let(:cask_token) { "latest-with-appcast" }
+        it { is_expected.to warn_with(error_msg) }
+      end
+    end
+
     describe "preferred download URL formats" do
       let(:warning_msg) { /URL format incorrect/ }
 

Library/Homebrew/test/support/fixtures/cask/Casks/latest-with-appcast.rb

@@ -0,0 +1,11 @@
+cask 'latest-with-appcast' do
+  version :latest
+  sha256 :no_check
+
+  url "file://#{TEST_FIXTURE_DIR}/cask/caffeine.zip"
+  appcast 'http://example.com/appcast.xml',
+          checkpoint: '67cdb8a02803ef37fdbf7e0be205863172e41a561ca446cd84f0d7ab35a99d94'
+  homepage 'http://example.com/with-appcast'
+
+  app 'Caffeine.app'
+end