Allow casks with outdated caskfiles to be reinstalled

The problem occurred when calling `brew reinstall` on a cask
with an out of date caskfile.

To solve the problem Cask::Installer#uninstall_existing_cask has been changed to
catch a possible CaskInvalidError when trying to load outdated
caskfiles using Cask::CaskLoader#load.

Library/Homebrew/cask/installer.rb

@@ -155,7 +155,11 @@ module Cask
 
       # use the same cask file that was used for installation, if possible
       installed_caskfile = @cask.installed_caskfile
-      installed_cask = installed_caskfile.exist? ? CaskLoader.load(installed_caskfile) : @cask
+      installed_cask = begin
+        installed_caskfile.exist? ? CaskLoader.load(installed_caskfile) : @cask
+      rescue CaskInvalidError # could be thrown by call to CaskLoader#load with outdated caskfile
+        @cask # default
+      end
 
       # Always force uninstallation, ignore method parameter
       cask_installer = Installer.new(installed_cask, verbose: verbose?, force: true, upgrade: upgrade?)

Library/Homebrew/test/cask/cask_loader/from__path_loader_spec.rb

@@ -34,5 +34,14 @@ describe Cask::CaskLoader::FromPathLoader do
         }.to raise_error(Cask::CaskUnreadableError, /undefined local variable or method/)
       end
     end
+
+    context "when the file contains an outdated cask" do
+      it "raises an error" do
+        expect {
+          described_class.new(cask_path("invalid/invalid-depends-on-macos-bad-release")).load(config: nil)
+        }.to raise_error(Cask::CaskInvalidError,
+                         /invalid 'depends_on macos' value: unknown or unsupported macOS version:/)
+      end
+    end
   end
 end

Library/Homebrew/test/cask/installer_spec.rb

@@ -251,4 +251,20 @@ describe Cask::Installer, :cask do
       expect(Cask::Caskroom.path.join("local-caffeine")).not_to be_a_directory
     end
   end
+
+  describe "uninstall_existing_cask" do
+    it "uninstalls when cask file is outdated" do
+      caffeine = Cask::CaskLoader.load(cask_path("local-caffeine"))
+      described_class.new(caffeine).install
+
+      expect(Cask::CaskLoader.load(cask_path("local-caffeine"))).to be_installed
+
+      expect(caffeine).to receive(:installed?).once.and_return(true)
+      outdate_caskfile = cask_path("invalid/invalid-depends-on-macos-bad-release")
+      expect(caffeine).to receive(:installed_caskfile).once.and_return(outdate_caskfile)
+      described_class.new(caffeine).uninstall_existing_cask
+
+      expect(Cask::CaskLoader.load(cask_path("local-caffeine"))).not_to be_installed
+    end
+  end
 end