resolves asciidoctor#185 autofit font size in listing & literal blocks

- reduce font size to prevent wrapping in listing & literal blocks
- activate if autofit option is specified on block
- activate if autofit-option attribute is specified on document

lib/asciidoctor-pdf/converter.rb

@@ -846,8 +846,8 @@ def convert_image node
     unlink_tmp_file image_path
   end
 
-  # TODO shrink text if it's too wide to fit in the bounding box
   def convert_listing_or_literal node
+    autofit = (node.option? 'autofit') || (node.document.attr? 'autofit-option')
     add_dest_for_block node if node.id
     # HACK disable built-in syntax highlighter; must be done before calling node.content!
     # NOTE the highlight sub is only set for coderay and pygments
@@ -861,16 +861,18 @@ def convert_listing_or_literal node
       highlighter = nil
       prev_subs = nil
     end
-    # FIXME source highlighter freaks out about the non-breaking space characters; does it?
     source_string = preserve_indentation node.content
+    longest_line = nil
     source_chunks = case highlighter
     when 'coderay'
       Helpers.require_library CodeRayRequirePath, 'coderay' unless defined? ::Asciidoctor::Prawn::CodeRayEncoder
+      longest_line = source_string.split(EOL).max_by &:length if autofit
       source_string, conum_mapping = extract_conums source_string
       fragments = (::CodeRay.scan source_string, (node.attr 'language', 'text', false).to_sym).to_prawn
       conum_mapping ? (restore_conums fragments, conum_mapping) : fragments
     when 'pygments'
       Helpers.require_library 'pygments', 'pygments.rb' unless defined? ::Pygments
+      longest_line = source_string.split(EOL).max_by &:length if autofit
       source_string, conum_mapping = extract_conums source_string
       lexer = ::Pygments::Lexer[node.attr 'language', 'text', false] || ::Pygments::Lexer['text']
       pygments_config = { nowrap: true, noclasses: true, style: (node.document.attr 'pygments-style') || 'pastie' }
@@ -879,14 +881,23 @@ def convert_listing_or_literal node
       conum_mapping ? (restore_conums fragments, conum_mapping) : fragments
     else
       # NOTE only format if we detect a need
-      (source_string =~ BuiltInEntityCharOrTagRx) ? (text_formatter.format source_string) : [{ text: source_string }]
+      if source_string =~ BuiltInEntityCharOrTagRx
+        longest_line = source_string.split(EOL).map {|l| unescape_builtin l }.max_by &:length if autofit
+        text_formatter.format source_string
+      else
+        longest_line = source_string.split(EOL).max_by &:length if autofit
+        [{ text: source_string }]
+      end
     end
 
     node.subs.replace prev_subs if prev_subs
 
     #move_down @theme.block_margin_top unless at_page_top?
     theme_margin :block, :top
 
+    # FIXME this calculation may overcompensate if callout numbers or inline formatting are present in line
+    adjusted_font_size = autofit ? (theme_font_size_autofit longest_line, :code) : nil
+
     keep_together do |box_height = nil|
       caption_height = node.title? ? (layout_caption node) : 0
       theme_font :code do
@@ -909,7 +920,7 @@ def convert_listing_or_literal node
         end
 
         pad_box @theme.code_padding do
-          typeset_formatted_text source_chunks, (calc_line_metrics @theme.code_line_height), color: (@theme.code_font_color || @font_color)
+          typeset_formatted_text source_chunks, (calc_line_metrics @theme.code_line_height), color: (@theme.code_font_color || @font_color), size: adjusted_font_size
         end
       end
     end
@@ -1985,6 +1996,26 @@ def theme_font category, opts = {}
     @text_transform = prev_transform if transform
   end
 
+  def theme_font_size_autofit line, category
+    adjusted_font_size = nil
+    if (padding = @theme[%(#{category}_padding)])
+      _, p_right, _, p_left = (::Array === padding) ? padding : ([padding] * 4)
+    else
+      p_right = p_left = 0
+    end
+    theme_font category do
+      indent p_left, p_right do
+        if (actual_width = width_of line) > (available_width = bounds.width)
+          # this calculation works if we assume code is monospaced
+          adjusted_font_size = (((available_width * font_size).to_f / actual_width) * 1000.0).floor / 1000.0
+        else
+          adjusted_font_size = font_size
+        end
+      end
+    end
+    adjusted_font_size
+  end
+
   # TODO document me, esp the first line formatting functionality
   def typeset_text string, line_metrics, opts = {}
     move_down line_metrics.padding_top

lib/asciidoctor-pdf/sanitizer.rb

@@ -25,6 +25,16 @@ def sanitize string
         .gsub(BuiltInEntityCharRx, BuiltInEntityChars)
   end
 
+  def unescape_all string
+    string
+      .gsub(NumericCharRefRx) { [$1.to_i].pack('U*') }
+      .gsub(BuiltInEntityCharRx, BuiltInEntityChars)
+  end
+
+  def unescape_builtin string
+    string.gsub(BuiltInEntityCharRx, BuiltInEntityChars)
+  end
+
   def upcase_pcdata string
     if BuiltInEntityCharOrTagRx =~ string
       string.gsub(SegmentPcdataRx) { $2 ? $2.upcase : $1 }