resolves asciidoctor#1372 set localyear and docyear attributes

lib/asciidoctor.rb

@@ -1324,6 +1324,7 @@ def load input, options = {}
       attributes['docname'] = Helpers.basename input_path, (attributes['docfilesuffix'] = ::File.extname input_path)
       docdate = (attributes['docdate'] ||= input_mtime.strftime('%Y-%m-%d'))
       doctime = (attributes['doctime'] ||= input_mtime.strftime('%H:%M:%S %Z'))
+      attributes['docyear'] ||= input_mtime.year
       attributes['docdatetime'] = %(#{docdate} #{doctime})
     elsif input.respond_to? :readlines
       # NOTE tty, pipes & sockets can't be rewound, but can't be sniffed easily either

lib/asciidoctor/document.rb

@@ -404,6 +404,7 @@ def initialize data = nil, options = {}
       # See https://reproducible-builds.org/specs/source-date-epoch/
       now = ::ENV['SOURCE_DATE_EPOCH'] ? (::Time.at ::ENV['SOURCE_DATE_EPOCH'].to_i).utc : ::Time.now
       localdate = (attrs['localdate'] ||= now.strftime('%Y-%m-%d'))
+      localyear = (attrs['localyear'] ||= now.year)
       unless (localtime = attrs['localtime'])
         begin
           localtime = attrs['localtime'] = now.strftime('%H:%M:%S %Z')
@@ -415,7 +416,7 @@ def initialize data = nil, options = {}
 
       # docdate, doctime and docdatetime should default to
       # localdate, localtime and localdatetime if not otherwise set
-      attrs['docdate'] ||= localdate
+      attrs['docyear'] ||= localyear
       attrs['doctime'] ||= localtime
       attrs['docdatetime'] ||= %(#{localdate} #{localtime})