resolves #1606 pass cloaked context to block extension (PR #1986)

- pass cloaked context as cloaked-context attribute to process method of custom block extension

lib/asciidoctor/parser.rb

@@ -871,14 +871,15 @@ def self.next_block(reader, parent, attributes = {}, options = {})
 
         else
           if block_extensions && (extension = extensions.registered_for_block?(block_context, cloaked_context))
-            # TODO pass cloaked_context to extension somehow (perhaps a new instance for each cloaked_context?)
             if (content_model = extension.config[:content_model]) != :skip
               if !(pos_attrs = extension.config[:pos_attrs] || []).empty?
                 AttributeList.rekey(attributes, [nil].concat(pos_attrs))
               end
               if (default_attrs = extension.config[:default_attrs])
                 default_attrs.each {|k, v| attributes[k] ||= v }
               end
+              # QUESTION should we clone the extension for each cloaked context and set in config?
+              attributes['cloaked-context'] = cloaked_context
             end
             block = build_block block_context, content_model, terminator, parent, reader, attributes, :extension => extension
             unless block && content_model != :skip

test/extensions_test.rb

@@ -556,6 +556,33 @@ def activate registry
       end
     end
 
+    test 'should pass cloaked context in attributes passed to process method of custom block' do
+      input = <<-EOS
+[custom]
+****
+sidebar
+****
+      EOS
+
+      cloaked_context = nil
+      begin
+        Asciidoctor::Extensions.register do
+          block :custom do
+            on_context :sidebar
+            process do |doc, reader, attrs|
+              cloaked_context = attrs['cloaked-context']
+              nil
+            end
+          end
+        end
+
+        render_embedded_string input
+        assert_equal :sidebar, cloaked_context
+      ensure
+        Asciidoctor::Extensions.unregister_all
+      end
+    end
+
     test 'should invoke processor for custom block macro' do
       input = <<-EOS
 snippet::12345[]