Fix SecurityErrors when loading data in safe mode.

Recent Ruby releases will raise a "SecurityError: Insecure operation -
require" exception when requiring a relative path name in safe mode.

Calculate the full path to the data file for use in require.

Similar to the changes made for 2.0.0, but doesn't raise an exception if
tzinfo/data can't be found when RubyDataSource is initialized.

lib/tzinfo/ruby_data_source.rb

@@ -15,6 +15,24 @@ class RubyDataSource < DataSource
     # Whether the country index has been loaded yet.
     @@country_index_loaded = false
 
+    # Initializes a new RubyDataSource instance.
+    def initialize
+      tzinfo_data = File.join('tzinfo', 'data')
+      begin
+        require(tzinfo_data)
+
+        data_file = File.join('', 'tzinfo', 'data.rb')
+        path = $".reverse_each.detect {|p| p.end_with?(data_file) }
+        if path
+          @base_path = File.join(File.dirname(path), 'data').untaint
+        else
+          @base_path = tzinfo_data
+        end
+      rescue LoadError
+        @base_path = tzinfo_data
+      end
+    end
+
     # Returns a TimezoneInfo instance for a given identifier. 
     # Raises InvalidTimezoneIdentifier if the timezone is not found or the 
     # identifier is invalid.
@@ -93,27 +111,17 @@ def require_definition(identifier)
     end
 
     # Requires an index by its name.
-    def self.require_index(name)
+    def require_index(name)
       require_data(*['indexes', name])
     end
 
     # Requires a file from tzinfo/data.
     def require_data(*file)
-      self.class.require_data(*file)
-    end
-
-    # Requires a file from tzinfo/data.
-    def self.require_data(*file)
-      require File.join('tzinfo', 'data', *file)
+      require(File.join(@base_path, *file))
     end
 
     # Loads in the index of timezones if it hasn't already been loaded.
     def load_timezone_index
-      self.class.load_timezone_index
-    end
-
-    # Loads in the index of timezones if it hasn't already been loaded.
-    def self.load_timezone_index
       unless @@timezone_index_loaded
         require_index('timezones')
         @@timezone_index_loaded = true
@@ -122,11 +130,6 @@ def self.load_timezone_index
 
     # Loads in the index of countries if it hasn't already been loaded.
     def load_country_index
-      self.class.load_country_index
-    end
-
-    # Loads in the index of countries if it hasn't already been loaded.
-    def self.load_country_index
       unless @@country_index_loaded
         require_index('countries')
         @@country_index_loaded = true

test/tc_ruby_data_source.rb

@@ -7,6 +7,22 @@ def setup
     @data_source = RubyDataSource.new
   end
 
+  def test_initialize_not_found
+    # A failure to load tzinfo/data in initialize will not cause an exception.
+    # Attempts to load data files will subsequently fail.
+    code = <<-EOF
+      begin
+        ds = TZInfo::RubyDataSource.new
+        puts 'Initialized'
+        ds.load_timezone_info('Europe/London')
+      rescue Exception => e
+        puts e.class
+      end
+    EOF
+
+    assert_sub_process_returns(['Initialized', 'TZInfo::InvalidTimezoneIdentifier'], code)
+  end
+
   def test_load_timezone_info_data
     info = @data_source.load_timezone_info('Europe/London')
     assert_kind_of(DataTimezoneInfo, info)