FEATURE: Add support for Unicode usernames and group names

Co-authored-by: Joffrey JAFFEUX <j.jaffeux@gmail.com>

lib/validators/external_system_avatars_validator.rb

@@ -0,0 +1,13 @@
+class ExternalSystemAvatarsValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  def valid_value?(value)
+    @valid = value == "t" || !SiteSetting.unicode_usernames
+  end
+
+  def error_message
+    I18n.t("site_settings.errors.unicode_usernames_avatars") if !@valid
+  end
+end

lib/validators/unicode_username_validator.rb

@@ -0,0 +1,13 @@
+class UnicodeUsernameValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  def valid_value?(value)
+    @valid = SiteSetting.external_system_avatars_enabled || value == "f"
+  end
+
+  def error_message
+    I18n.t("site_settings.errors.unicode_usernames_avatars") if !@valid
+  end
+end

lib/validators/unicode_username_whitelist_validator.rb

@@ -0,0 +1,26 @@
+class UnicodeUsernameWhitelistValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  def valid_value?(value)
+    @error_message = nil
+    return true if value.blank?
+
+    if value.match?(/^\/.*\/[imxo]*$/)
+      @error_message = I18n.t("site_settings.errors.unicode_username_whitelist.leading_trailing_slash")
+    else
+      begin
+        Regexp.new(value)
+      rescue RegexpError => e
+        @error_message = I18n.t("site_settings.errors.unicode_username_whitelist.regex_invalid", error: e.message)
+      end
+    end
+
+    @error_message.blank?
+  end
+
+  def error_message
+    @error_message
+  end
+end