(MODULES-2175) Handle symlink missing target path

When the target for a symlink no longer exists, attempting to unlink
the symlink with `Puppet::FileSystem.unlink` fails with a `Permission
Denied` error. If the target path doesn't exist, fall back to moving
the existing link in the same way we would if it were a file or
directory.

lib/puppet/feature/vendors_dsc.rb

@@ -17,16 +17,29 @@ def self.set_symlink_folder
                 Puppet::FileSystem.readlink(puppet_modules_vendor_folder) == vendored_modules_path
 
       if Puppet::FileSystem.symlink?(puppet_modules_vendor_folder)
-        Puppet::FileSystem.unlink(puppet_modules_vendor_folder)
+        begin
+          Puppet::FileSystem.unlink(puppet_modules_vendor_folder)
+        rescue => e
+          # If the target path doesn't exist, unlinking will fail.
+          # Instead prefer to move the path so the link creation
+          # can occur successfully.
+          Puppet.warning "Error occurred attempting to remove old symlink. It's likely the target path no longer exists. Renaming the link instead."
+          append_location_with_current_date_time puppet_modules_vendor_folder
+        end
       elsif Puppet::FileSystem.exist?(puppet_modules_vendor_folder)
-        FileUtils.mv puppet_modules_vendor_folder, "#{puppet_modules_vendor_folder}.#{Time.now.utc.strftime("%Y%m%d_%H%M%S_%L")}"
+        append_location_with_current_date_time puppet_modules_vendor_folder
       end
 
       Puppet.debug "Creating symlink at '#{puppet_modules_vendor_folder}' \n pointed to '#{vendored_modules_path}'."
       Puppet::FileSystem.dir_mkpath(puppet_modules_vendor_folder) if !Puppet::FileSystem.dir_exist?(puppet_modules_vendor_folder)
       Puppet::FileSystem.symlink(vendored_modules_path, puppet_modules_vendor_folder,{ :force => true})
     end
 
+    # Add the current date time as a string to the end of an existing location.
+    def self.append_location_with_current_date_time(existing_location)
+      FileUtils.mv existing_location, "#{existing_location}.#{Time.now.utc.strftime("%Y%m%d_%H%M%S_%L")}"
+    end
+
     # Get the non-x86 program files path, no matter whether the process is
     # a 32 bit or 64 bit process. Shut off registry redirection and query
     # the ProgramFilesDir key to retrieve the program files value.

spec/integration/puppet/feature/vendors_dsc_spec.rb

@@ -40,19 +40,28 @@ def set_symlink_and_check
     end
 
     it "should recreate a symlink if the existing link path is wrong" do
-      FileUtils.mkdir_p(program_files)
-      Puppet::FileSystem.symlink(subject.vendored_modules_path, Dir.mktmpdir('dsc_link'), { :force => true})
+      FileUtils.mkdir_p(::File.expand_path('..', vendored_modules_symlink_path))
+      Puppet::FileSystem.symlink(Dir.mktmpdir('dsc_link'), vendored_modules_symlink_path, { :force => true})
+
+      set_symlink_and_check
+    end
+
+    it "should recreate a symlink if the existing link path does not exist" do
+      FileUtils.mkdir_p(::File.expand_path('..', vendored_modules_symlink_path))
+      link_target = Dir.mktmpdir('dsc_link')
+      Puppet::FileSystem.symlink(link_target, vendored_modules_symlink_path, { :force => true})
+      system("rmdir /s /q \"#{link_target}\"")
 
       set_symlink_and_check
     end
 
-    it "should recreate a symlink if the existing path is a directory" do
+    it "should create a symlink if the existing path is a directory" do
       FileUtils.mkdir_p(vendored_modules_symlink_path)
 
       set_symlink_and_check
     end
 
-    it "should recreate a symlink if the existing path is a file" do
+    it "should create a symlink if the existing path is a file" do
       FileUtils.mkdir_p(::File.expand_path('..', vendored_modules_symlink_path))
       FileUtils.touch vendored_modules_symlink_path
 

spec/unit/puppet/feature/vendors_dsc_spec.rb

@@ -77,6 +77,20 @@ module DscSymlink; end # for tests on non-Windows
         subject.set_symlink_folder
       end
 
+      it "should recreate a symlink if the existing link path does not exist" do
+        Puppet::FileSystem.expects(:symlink?).returns(true).times(2)
+        Puppet::FileSystem.expects(:readlink).returns('C:\dsc')
+        Puppet::FileSystem.expects(:unlink).raises(StandardError.new(3),'Permission denied')
+        FileUtils.expects(:mv)
+        Puppet::FileSystem.expects(:dir_exist?).returns(true)
+        Puppet::FileSystem.expects(:symlink)
+
+        Puppet::FileSystem.expects(:exist?).never
+        Puppet::FileSystem.expects(:dir_mkpath).never
+
+        subject.set_symlink_folder
+      end
+
       it "should create a symlink if the existing path is not a symlink" do
         Puppet::FileSystem.expects(:symlink?).returns(false).times(2)
         Puppet::FileSystem.expects(:exist?).returns(true)