resolves asciidoctor#236 expand tabs to spaces based on value of tabs…

…ize attribute

lib/asciidoctor-pdf/converter.rb

@@ -34,6 +34,7 @@ def self.unicode_char number
   # NOTE require_library doesn't support require_relative and we don't modify the load path for this gem
   CodeRayRequirePath = ::File.join((::File.dirname __FILE__), 'prawn_ext/coderay_encoder')
 
+  AsciidoctorVersion = ::Gem::Version.create ::Asciidoctor::VERSION
   AdmonitionIcons = {
     caution:   { key: 'fa-fire', color: 'BF3400' },
     important: { key: 'fa-exclamation-circle', color: 'BF0000' },
@@ -42,8 +43,10 @@ def self.unicode_char number
     warning:   { key: 'fa-exclamation-triangle', color: 'BF6900' }
   }
   Alignments = [:left, :center, :right]
-  IndentationRx = /^ +/
-  TabSpaces = ' ' * 4
+  EOL = "\n"
+  TAB = "\t"
+  LeadingSpaceRx = /^ /
+  LeadingTabsRx = /^\t+/
   NoBreakSpace = unicode_char 0x00a0
   NarrowSpace = unicode_char 0x2009
   NarrowNoBreakSpace = unicode_char 0x202f
@@ -78,6 +81,9 @@ def initialize backend, opts
     #htmlsyntax 'xml'
     @list_numbers = []
     @list_bullets = []
+    @capabilities = {
+      explicit_tabsize: AsciidoctorVersion >= (::Gem::Version.create '1.5.3')
+    }
   end
 
   def convert node, name = nil, opts = {}
@@ -482,7 +488,8 @@ def convert_quote_or_verse node
           if node.context == :quote
             convert_content_for_block node
           else # verse
-            layout_prose node.content, preserve: true, normalize: false, align: :left
+            content = preserve_space node.content, (node.attr 'tabsize')
+            layout_prose content, normalize: false, align: :left
           end
         end
         theme_font :blockquote_cite do
@@ -881,7 +888,7 @@ def convert_listing_or_literal node
       highlighter = nil
       prev_subs = nil
     end
-    source_string = preserve_indentation node.content
+    source_string = preserve_space node.content, (node.attr 'tabsize')
     source_chunks = case highlighter
     when 'coderay'
       Helpers.require_library CodeRayRequirePath, 'coderay' unless defined? ::Asciidoctor::Prawn::CodeRayEncoder
@@ -1576,8 +1583,6 @@ def layout_prose string, opts = {}
         string = %(<a anchor="#{anchor}">#{string}</a>)
       end
     end
-    # preserve leading space using non-breaking space chars
-    string = preserve_indentation string if opts.delete :preserve
     margin_top top_margin
     typeset_text string, calc_line_metrics((opts.delete :line_height) || @theme.base_line_height), {
       color: @font_color,
@@ -2133,8 +2138,52 @@ def height_of_typeset_text string, opts = {}
     (height_of string, leading: line_metrics.leading, final_gap: line_metrics.final_gap) + line_metrics.padding_top + line_metrics.padding_bottom
   end
 
-  def preserve_indentation string
-    string.gsub(IndentationRx) { NoBreakSpace * $&.length }
+  def preserve_space string, tab_size = nil
+    # FIXME tab logic shouldn't be necessary once 1.5.3 is out
+    if string.include? TAB
+      # Asciidoctor <= 1.5.2 already does tab replacement in some cases, so be consistent about tab size
+      tab_size = tab_size && @capabilities[:explicit_tabsize] ? tab_size.to_i : 4
+      full_tab_space = ' ' * tab_size
+      # NOTE '+' operator is faster than interpolation in this case
+      lead_tab_space = NoBreakSpace + full_tab_space.chop
+      result = []
+      string.each_line {|line|
+        if line.start_with? TAB
+          # NOTE '+' operator is faster than interpolation in this case
+          line.sub!(LeadingTabsRx) { lead_tab_space + (full_tab_space * ($&.length - 1)) }
+          leading_space = false
+        elsif line == EOL
+          result << line
+          next
+        else
+          leading_space = line.start_with? ' '
+        end
+
+        if line.include? TAB
+          spaces_added = 0
+          line.gsub!(TAB) {
+            if (offset = ($~.begin 0) + spaces_added) % tab_size == 0
+              spaces_added += (tab_size - 1)
+              full_tab_space
+            else
+              unless (spaces = tab_size - offset % tab_size) == 1
+                spaces_added += (spaces - 1)
+              end
+              ' ' * spaces
+            end
+          }
+        end
+
+        if leading_space
+          result << NoBreakSpace << line[1..-1]
+        else
+          result << line
+        end
+      }
+      result.join
+    else
+      string.gsub! LeadingSpaceRx, NoBreakSpace
+    end
   end
 
   # If an id is provided or the node passed as the first argument has an id,