(PUP-11629) Handles empty task metadata file

An empty string is valid JSON per the IETF standard, but a bug in
MultiJSON causes it to throw MultiJson::ParseError when loading
an empty JSON file.

This commit updates tasks to check for an empty JSON file to work
around this issue and instead will return an empty hash.

Author: mhashizume

lib/puppet/module/task.rb

@@ -232,7 +232,12 @@ def initialize(pup_module, task_name,  module_executables, metadata_file = nil)
     end
 
     def self.read_metadata(file)
-      Puppet::Util::Json.load(Puppet::FileSystem.read(file, :encoding => 'utf-8')) if file
+      # MultiJSON has a bug that improperly errors when loading an empty string
+      # so we handle it here for now. See: PUP-11629
+      if file
+        content = Puppet::FileSystem.read(file, :encoding => 'utf-8')
+        content.empty? ? {} : Puppet::Util::Json.load(content)
+      end
     rescue SystemCallError, IOError => err
       msg = _("Error reading metadata: %{message}" % {message: err.message})
       raise InvalidMetadata.new(msg, 'puppet.tasks/unreadable-metadata')

spec/unit/task_spec.rb

@@ -235,6 +235,17 @@
         tasks[0].metadata
       }.to raise_error(Puppet::Module::Task::InvalidMetadata, /whoops/)
     end
+
+    it 'returns empty hash for metadata when json metadata file is empty' do
+      FileUtils.mkdir_p(tasks_path)
+      FileUtils.touch(File.join(tasks_path, 'task.json'))
+      FileUtils.touch(File.join(tasks_path, 'task'))
+
+      tasks = Puppet::Module::Task.tasks_in_module(mymod)
+
+      expect(tasks.count).to eq(1)
+      expect(tasks[0].metadata).to eq({})
+    end
   end
 
   describe :validate do