Implement preserve filter

lib/hamlit/compilers/filter.rb

@@ -2,6 +2,7 @@ require 'hamlit/concerns/included'
 require 'hamlit/concerns/registerable'
 require 'hamlit/filters/escaped'
 require 'hamlit/filters/plain'
+require 'hamlit/filters/preserve'
 
 module Hamlit
   module Compilers
@@ -11,8 +12,9 @@ module Hamlit
       included do
         extend Concerns::Registerable
 
-        register :escaped, Filters::Escaped
-        register :plain,   Filters::Plain
+        register :escaped,  Filters::Escaped
+        register :plain,    Filters::Plain
+        register :preserve, Filters::Preserve
       end
 
       def on_haml_filter(name, lines)

lib/hamlit/concerns/line_reader.rb

@@ -32,12 +32,24 @@ module Hamlit
       def read_lines
         lines  = []
         spaces = ' ' * (@current_indent * 2)
-        while count_indent(next_line, strict: false) >= @current_indent
+        while read_line?
           lines << @lines[@current_lineno + 1].gsub(/\A#{spaces}/, '')
           @current_lineno += 1
         end
         lines
       end
+
+      private
+
+      def read_line?
+        return true if count_indent(next_line, strict: false) >= @current_indent
+
+        line = @lines[@current_lineno + 1]
+        return false unless line
+
+        # NOTE: preserve filter also requires an empty line
+        line.gsub(/ /, '').length == 0
+      end
     end
   end
 end

lib/hamlit/filters/plain.rb

@@ -3,7 +3,7 @@ module Hamlit
     class Plain
       def compile(lines)
         ast = [:multi]
-        text = lines.join("\n")
+        text = strip_last(lines).join("\n")
         ast << [:haml, :text, text]
         ast << [:static, "\n"] if string_interpolated?(text)
         ast
@@ -14,6 +14,14 @@ module Hamlit
       def string_interpolated?(text)
         text =~ /\#{[^\#{}]*}/
       end
+
+      def strip_last(lines)
+        lines = lines.dup
+        while lines.last && lines.last.length == 0
+          lines.delete_at(-1)
+        end
+        lines
+      end
     end
   end
 end

lib/hamlit/filters/preserve.rb

@@ -0,0 +1,13 @@
+require 'hamlit/helpers'
+
+module Hamlit
+  module Filters
+    class Preserve
+      def compile(lines)
+        ast = [:multi]
+        ast << [:haml, :text, lines.join('&#x000A;')]
+        ast
+      end
+    end
+  end
+end