allow custom converter to set backend info such as outfilesuffix

- add DSL for custom converter to use to set backend info
- add test to ensure outfilesuffix is set properly

6 files changed, 109 insertions, 24 deletions

diff --git a/lib/asciidoctor/converter.rb b/lib/asciidoctor/converter.rb
index 9698dbf1..d819f542 100644
--- a/lib/asciidoctor/converter.rb
+++ b/lib/asciidoctor/converter.rb
@@ -15,6 +15,10 @@ module Asciidoctor
   #   class TextConverter
   #     include Asciidoctor::Converter
   #     register_for 'text'
+  #     def initialize backend, opts
+  #       super
+  #       outfilesuffix '.txt'
+  #     end
   #     def convert node, transform = nil
   #       case (transform ||= node.node_name)
   #       when 'document'
@@ -63,6 +67,54 @@ module Asciidoctor
       end
     end
 
+    module BackendInfo
+      def backend_info
+        @backend_info ||= setup_backend_info
+      end
+
+      def setup_backend_info
+        raise ::ArgumentError, %(Cannot determine backend for converter: #{self.class}) unless @backend
+        base = @backend.sub TrailingDigitsRx, ''
+        if (ext = DEFAULT_EXTENSIONS[base])
+          type = ext[1..-1]
+        else
+          # QUESTION should we be forcing the basebackend to html if unknown?
+          base = 'html'
+          ext = '.html'
+          type = 'html'
+        end
+        {
+          'basebackend' => base,
+          'outfilesuffix' => ext,
+          'filetype' => type,
+        }
+      end
+
+      def filetype value = nil
+        if value
+          backend_info['filetype'] = value
+        else
+          backend_info['filetype']
+        end
+      end
+
+      def basebackend value = nil
+        if value
+          backend_info['basebackend'] = value
+        else
+          backend_info['basebackend']
+        end
+      end
+
+      def outfilesuffix value = nil
+        if value
+          backend_info['outfilesuffix'] = value
+        else
+          backend_info['outfilesuffix']
+        end
+      end
+    end
+
     class << self
       # Mixes the {Config Converter::Config} module into any class that includes the {Converter} module.
       #
@@ -75,7 +127,8 @@ module Asciidoctor
     end
   
     include Config
-  
+    include BackendInfo
+
     # Public: Creates a new instance of Converter
     #
     # backend - The String backend format to which this converter converts.
@@ -84,8 +137,19 @@ module Asciidoctor
     # Returns a new instance of [Converter]
     def initialize backend, opts = {}
       @backend = backend
+      setup_backend_info
     end
-  
+
+=begin
+    # Public: Invoked when this converter is added to the chain of converters in a {CompositeConverter}.
+    #
+    # owner - The CompositeConverter instance
+    #
+    # Returns nothing
+    def composed owner
+    end
+=end
+
     # Public: Converts an {AbstractNode} using the specified transform. If a
     # transform is not specified, implementations typically derive one from the
     # {AbstractNode#node_name} property.
diff --git a/lib/asciidoctor/converter/composite.rb b/lib/asciidoctor/converter/composite.rb
index d6f7fc99..09fdf4f9 100644
--- a/lib/asciidoctor/converter/composite.rb
+++ b/lib/asciidoctor/converter/composite.rb
@@ -3,11 +3,15 @@ module Asciidoctor
   # objects passed to the constructor. Selects the first {Converter} that
   # identifies itself as the handler for a given transform.
   class Converter::CompositeConverter < Converter::Base
+
     # Get the Array of Converter objects in the chain
     attr_reader :converters
 
-    def initialize *converters
-      @converters = converters.flatten.compact
+    def initialize backend, *converters
+      @backend = backend
+      (@converters = converters.flatten.compact).each do |converter|
+        converter.composed self if converter.respond_to? :composed
+      end
       @converter_map = {}
     end
 
diff --git a/lib/asciidoctor/converter/factory.rb b/lib/asciidoctor/converter/factory.rb
index 11378082..89491cbf 100644
--- a/lib/asciidoctor/converter/factory.rb
+++ b/lib/asciidoctor/converter/factory.rb
@@ -200,7 +200,7 @@ module Asciidoctor
         end
         template_converter = TemplateConverter.new backend, opts[:template_dirs], opts
         # QUESTION should we omit the composite converter if built_in_converter is nil?
-        CompositeConverter.new template_converter, base_converter
+        CompositeConverter.new backend, template_converter, base_converter
       end
     end
   end
diff --git a/lib/asciidoctor/converter/template.rb b/lib/asciidoctor/converter/template.rb
index 160f9772..ffa9ba65 100644
--- a/lib/asciidoctor/converter/template.rb
+++ b/lib/asciidoctor/converter/template.rb
@@ -78,6 +78,13 @@ module Asciidoctor
       #create_handlers
     end
 
+=begin
+    # Public: Called when this converter is added to a composite converter.
+    def composed parent
+      # TODO set the backend info determined during the scan
+    end
+=end
+
     # Internal: Scans the template directories specified in the constructor for Tilt-supported
     # templates, loads the templates and stores the in a Hash that is accessible via the
     # {TemplateConverter#templates} method.
diff --git a/lib/asciidoctor/document.rb b/lib/asciidoctor/document.rb
index eb45358c..85fdb7cb 100644
--- a/lib/asciidoctor/document.rb
+++ b/lib/asciidoctor/document.rb
@@ -775,24 +775,40 @@ class Document < AbstractBlock
       if (resolved_name = BACKEND_ALIASES[new_backend])
         new_backend = resolved_name
       end
-      new_basebackend = new_backend.sub TrailingDigitsRx, ''
-      if (page_width = DEFAULT_PAGE_WIDTHS[new_basebackend])
-        attrs['pagewidth'] = page_width
-      else
-        attrs.delete 'pagewidth'
-      end
       if current_backend
         attrs.delete %(backend-#{current_backend})
         if current_doctype
           attrs.delete %(backend-#{current_backend}-doctype-#{current_doctype})
         end
       end
-      attrs['backend'] = new_backend
-      attrs[%(backend-#{new_backend})] = ''
       if current_doctype
         attrs[%(doctype-#{current_doctype})] = ''
         attrs[%(backend-#{new_backend}-doctype-#{current_doctype})] = ''
       end
+      attrs['backend'] = new_backend
+      attrs[%(backend-#{new_backend})] = ''
+      # (re)initialize converter
+      if (@converter = create_converter).is_a? Converter::BackendInfo
+        new_basebackend = @converter.basebackend
+        attrs['outfilesuffix'] = @converter.outfilesuffix
+        new_filetype = @converter.filetype
+      else
+        new_basebackend = new_backend.sub TrailingDigitsRx, ''
+        # QUESTION should we be forcing the basebackend to html if unknown?
+        new_outfilesuffix = DEFAULT_EXTENSIONS[new_basebackend] || '.html'
+        new_filetype = new_outfilesuffix[1..-1]
+        attrs['outfilesuffix'] = new_outfilesuffix unless attribute_locked? 'outfilesuffix'
+      end
+      if (current_filetype = attrs['filetype'])
+        attrs.delete %(filetype-#{current_filetype})
+      end
+      attrs['filetype'] = new_filetype
+      attrs[%(filetype-#{new_filetype})] = ''
+      if (page_width = DEFAULT_PAGE_WIDTHS[new_basebackend])
+        attrs['pagewidth'] = page_width
+      else
+        attrs.delete 'pagewidth'
+      end
       if new_basebackend != current_basebackend
         if current_basebackend
           attrs.delete %(basebackend-#{current_basebackend})
@@ -804,17 +820,8 @@ class Document < AbstractBlock
         attrs[%(basebackend-#{new_basebackend})] = ''
         attrs[%(basebackend-#{new_basebackend}-doctype-#{current_doctype})] = '' if current_doctype
       end
-      ext = DEFAULT_EXTENSIONS[new_basebackend] || '.html'
-      new_file_type = ext[1..-1]
-      current_file_type = attrs['filetype']
-      attrs['outfilesuffix'] = ext unless attribute_locked? 'outfilesuffix'
-      attrs.delete %(filetype-#{current_file_type}) if current_file_type
-      attrs['filetype'] = new_file_type
-      attrs[%(filetype-#{new_file_type})] = ''
-      # clear cached value
+      # clear cached backend value
       @backend = nil
-      # (re)initialize converter
-      @converter = create_converter
     end
   end
 
@@ -833,7 +840,7 @@ class Document < AbstractBlock
       attrs[%(doctype-#{new_doctype})] = ''
       attrs[%(backend-#{current_backend}-doctype-#{new_doctype})] = '' if current_backend
       attrs[%(basebackend-#{current_basebackend}-doctype-#{new_doctype})] = '' if current_basebackend
-      # clear cached value
+      # clear cached doctype value
       @doctype = nil
     end
   end
diff --git a/test/attributes_test.rb b/test/attributes_test.rb
index f6b588a8..ad3000ed 100644
--- a/test/attributes_test.rb
+++ b/test/attributes_test.rb
@@ -162,6 +162,7 @@ content
         'backend' => 'html5',
         'backend-html5' => '',
         'backend-html5-doctype-article' => '',
+        'outfilesuffix' => '.html',
         'basebackend' => 'html',
         'basebackend-html' => '',
         'basebackend-html-doctype-article' => '',
@@ -189,6 +190,7 @@ content
         'backend' => 'docbook5',
         'backend-docbook5' => '',
         'backend-docbook5-doctype-book' => '',
+        'outfilesuffix' => '.xml',
         'basebackend' => 'docbook',
         'basebackend-docbook' => '',
         'basebackend-docbook-doctype-book' => '',
@@ -218,6 +220,7 @@ content
         'backend' => 'docbook5',
         'backend-docbook5' => '',
         'backend-docbook5-doctype-book' => '',
+        'outfilesuffix' => '.xml',
         'basebackend' => 'docbook',
         'basebackend-docbook' => '',
         'basebackend-docbook-doctype-book' => '',