resolves asciidoctor#57 make front matter header optional

README.adoc

@@ -117,7 +117,7 @@ There are a few conditions that must be met for an AsciiDoc file to be qualified
 . The file must have an AsciiDoc file extension (see <<configuration>>).
 . The name of the file must not begin with a dot (`.`) or underscore (`_`).footnoteref:[excluded_files,These files are excluded by Jekyll.]
 . The file must not be located in a folder whose name begins with a dot (`.`) or underscore (`_`), except for posts.footnoteref:[excluded_files]
-. The document must begin with a {uri-front-matter}[front matter header] (and cannot have a Byte Order Mark, or BOM).
+//. The document may begin with a {uri-front-matter}[front matter header] (in which case it cannot begin with a Byte Order Mark, or BOM).
 
 Here's a sample AsciiDoc file that meets these criteria:
 
@@ -171,15 +171,14 @@ If you want the Liquid template preprocessor to be applied to an AsciiDoc file (
 :page-liquid:
 ----
 
-IMPORTANT: Each AsciiDoc file must begin with a {uri-front-matter}[front matter header].
-Otherwise, Jekyll won't treat the file as a page, but rather as a static file.
-The front matter header must be the very first character of the file.
-If the file begins with whitespace or a Byte Order Mark (BOM), then the front matter header won't be seen.
+IMPORTANT: AsciiDoc files may include a {uri-front-matter}[front matter header] for declaring page settings and variables.
+If present, the front matter header must be the very first character of the file.
+The front matter header won't be seen if the file begins with whitespace or a Byte Order Mark (BOM).
 
-TIP: You can use an empty front matter header, as shown in the second example above.
-In this case, you define all the document metadata (e.g., layout) using AsciiDoc attributes instead of in the front matter.
+TIP: You can exclude the front matter header, as shown in the first example above, or leave it empty, as shown in the second example.
+In these cases, you'll define all the page metadata (e.g., layout) using AsciiDoc attributes instead of in the front matter.
 You can also use a combination of both.
-In this case, the attributes defined in the AsciiDoc header take precedence.
+When combined, the attributes defined in the AsciiDoc header take precedence.
 
 You can now build your site using:
 

lib/jekyll-asciidoc.rb

@@ -1,6 +1,15 @@
 JEKYLL_MIN_VERSION_3 = Gem::Version.new(Jekyll::VERSION) >= Gem::Version.new('3.0.0') unless defined? JEKYLL_MIN_VERSION_3
 
 module Jekyll
+  module AsciiDoc
+    module Utils
+      extend self
+      def has_front_matter?(delegate_method, asciidoc_ext_re, path)
+        ::File.extname(path) =~ asciidoc_ext_re ? true : delegate_method.call(path)
+      end
+    end
+  end
+
   module Converters
     class AsciiDocConverter < Converter
       IMPLICIT_ATTRIBUTES = %W(
@@ -17,7 +26,7 @@ def initialize(config)
         @config = config
         config['asciidoc'] ||= 'asciidoctor'
         asciidoc_ext = (config['asciidoc_ext'] ||= 'asciidoc,adoc,ad')
-        config['asciidoc_ext_re'] = /^\.(?:#{asciidoc_ext.tr ',', '|'})$/i
+        asciidoc_ext_re = (config['asciidoc_ext_re'] = /^\.(?:#{asciidoc_ext.tr ',', '|'})$/i)
         config['asciidoc_page_attribute_prefix'] ||= 'page'
         unless (asciidoctor_config = (config['asciidoctor'] ||= {})).frozen?
           # NOTE convert keys to symbols
@@ -29,6 +38,14 @@ def initialize(config)
             attributes.unshift('notitle', 'hardbreaks', 'idprefix', 'idseparator=-', 'linkattrs')
             attributes.concat(IMPLICIT_ATTRIBUTES)
           end
+          if JEKYLL_MIN_VERSION_3 && !config['asciidoc_require_front_matter']
+            if (del_method = ::Jekyll::Utils.method(:has_yaml_header?))
+              unless (new_method = ::Jekyll::AsciiDoc::Utils.method(:has_front_matter?)).respond_to?(:curry)
+                new_method = new_method.to_proc # Ruby < 2.2
+              end
+              del_method.owner.define_singleton_method(:has_yaml_header?, new_method.curry[del_method][asciidoc_ext_re])
+            end
+          end
           asciidoctor_config.freeze
         end
       end