Add tags backend

converters/tags.rb

@@ -0,0 +1,40 @@
+require 'json'
+
+class TagsConverter
+  include Asciidoctor::Converter
+  register_for("tags")
+
+  @tag_map = {}
+  @prefix = ""
+
+  def initialize(backend, opts = {})
+    super
+    outfilesuffix(".tags.json")
+    # Pass `-a tags-prefix=qx_` to only include tags starting with `qx_`.
+    @prefix = opts[:document].attributes.fetch("tags-prefix", "")
+  end
+
+  # `node` is an `AbstractNode`.
+  def convert(node, transform = node.node_name, opts = nil)
+    if transform == "document" then
+      @tag_map = {}
+      # Calling node.content will recursively call convert() on all the nodes
+      # and also expand blocks, creating inline nodes. We call this to convert
+      # all nodes to text, and record their content in the tag map. Then we
+      # throw away the text and output the tag map as JSON instead.
+      node.content
+      JSON.pretty_generate({
+        "tags": @tag_map,
+      })
+    else
+      # Output the text content of this node.
+      content = if node.inline? then node.text else node.content end
+      unless node.id.nil?
+        if node.id.start_with?(@prefix)
+          @tag_map[node.id] = content
+        end
+      end
+      content
+    end
+  end
+end