1 files changed, 29 insertions, 0 deletions
diff --git a/lib/extensions/section_id_validator.rb b/lib/extensions/section_id_validator.rb
new file mode 100644
index 0000000..2ad496c
--- /dev/null
+++ b/lib/extensions/section_id_validator.rb
@@ -0,0 +1,29 @@
+module Nuldoc
+  module Extensions
+    class SectionIdValidator < Asciidoctor::Extensions::TreeProcessor
+      def process(doc)
+        errors = []
+        (doc.find_by(context: :section) {_1.level > 0}).each do |section|
+          errors << validate_section(section)
+        end
+        error_message = errors.compact.join("\n")
+        unless error_message.empty?
+          raise "SectionIdValidator (#{doc.attributes['source-file-path']}):\n#{error_message}"
+        end
+      end
+
+      private
+
+      def validate_section(section)
+        id = section.id
+        unless id
+          return "Section '#{section.title}': each section MUST have an id."
+        end
+        unless id.match?(/\A[-0-9a-z]+\z/)
+          return "Section '#{section.title}' (##{id}): section id MUST consist of either hyphen, digits or lowercases."
+        end
+        nil
+      end
+    end
+  end
+end