added labels for datetime

cf https://stackoverflow.com/a/47836699

config/initializers/date_select.rb

@@ -0,0 +1,49 @@
+# We monkey patch the DateTimeSelector in order to add accessibility labels
+# https://stackoverflow.com/a/47836699
+module ActionView
+  module Helpers
+    class DateTimeSelector
+      # Given an ordering of datetime components, create the selection HTML
+      # and join them with their appropriate separators.
+      def build_selects_from_types(order)
+        select = ""
+        order.reverse_each do |type|
+          separator = separator(type)
+          select.insert(0, separator.to_s + send("select_#{type}").to_s)
+        end
+        # rubocop:disable Rails/OutputSafety
+        select.html_safe
+        # rubocop:enable Rails/OutputSafety
+      end
+
+      def datetime_accessibility_label(n, label)
+        prefix_re = @options[:prefix].match('(.*)\[(.*)\]\[(\d+)\]')
+        if prefix_re.nil? || prefix_re.size < 2
+          prefix = []
+        else
+          prefix = prefix_re.to_a.drop(1)
+        end
+        field_for = "#{prefix.join('_')}_#{@options[:field_name]}"
+
+        "<span class='hidden'><label for='#{field_for}_#{n}i'>#{label}</label></span>"
+      end
+
+      # Returns the separator for a given datetime component.
+      def separator(type)
+        return "" if @options[:use_hidden]
+        case type
+        when :year
+          datetime_accessibility_label(1, 'Année')
+        when :month
+          datetime_accessibility_label(2, 'Mois')
+        when :day
+          datetime_accessibility_label(3, 'Jour')
+        when :hour
+          (@options[:discard_year] && @options[:discard_day]) ? "" : @options[:datetime_separator] + datetime_accessibility_label(4, 'Heure')
+        when :minute, :second
+          @options[:"discard_#{type}"] ? "" : datetime_accessibility_label(5, 'Minute')
+        end
+      end
+    end
+  end
+end