Accept string interpolation in sass filter

lib/hamlit/compilers/text.rb

@@ -1,21 +1,15 @@
-require 'hamlit/concerns/string_literal'
+require 'hamlit/concerns/string_interpolation'
 
 module Hamlit
   module Compilers
     module Text
-      include Concerns::StringLiteral
+      include Concerns::StringInterpolation
 
       def on_haml_text(exp)
         return [:static, exp] unless contains_interpolation?(exp)
 
         [:dynamic, string_literal(exp)]
       end
-
-      private
-
-      def contains_interpolation?(str)
-        /#[\{$@]/ === str
-      end
     end
   end
 end

lib/hamlit/concerns/string_interpolation.rb

@@ -1,10 +1,14 @@
 module Hamlit
   module Concerns
-    module StringLiteral
+    module StringInterpolation
       def string_literal(str)
         unescape_interpolation(str)
       end
 
+      def contains_interpolation?(str)
+        /#[\{$@]/ === str
+      end
+
       private
 
       def unescape_interpolation(str)

lib/hamlit/filters/base.rb

@@ -3,7 +3,12 @@ module Hamlit
     class Base
       attr_reader :options
 
-      def initialize(options)
+      def self.indent_source(source, indent_width: 0)
+        lines = source.split("\n")
+        self.new.compile_lines(lines, indent_width: indent_width)
+      end
+
+      def initialize(options = {})
         @options = options
       end
 
@@ -11,8 +16,6 @@ module Hamlit
         raise NotImplementedError
       end
 
-      private
-
       def compile_lines(lines, indent_width: 0)
         base  = (lines.first || '').index(/[^\s]/) || 0
         width = indent_width - base
@@ -26,6 +29,8 @@ module Hamlit
         text
       end
 
+      private
+
       # NOTE: empty line is reserved for preserve filter.
       def strip_last(lines)
         lines = lines.dup

lib/hamlit/filters/sass.rb

@@ -1,21 +1,11 @@
-require 'tilt'
-require 'hamlit/filters/base'
+require 'hamlit/filters/tilt'
 
 module Hamlit
   module Filters
-    class Sass < Base
+    class Sass < Filters::Tilt
       def compile(lines)
-        result  = compile_with_tilt(lines)
-        content = [:multi, [:static, "\n"], result]
-        [:html, :tag, 'style', [:html, :attrs], content]
-      end
-
-      private
-
-      def compile_with_tilt(lines)
-        source = lines.join("\n")
-        result = ::Tilt['t.sass'].new { source }.render
-        [:static, compile_lines(result.split("\n"), indent_width: 2)]
+        ast = [:html, :tag, 'style', [:html, :attrs]]
+        compile_with_tilt('sass', lines.join("\n"), ast)
       end
     end
   end

lib/hamlit/filters/tilt.rb

@@ -0,0 +1,33 @@
+require 'tilt'
+require 'hamlit/concerns/string_interpolation'
+require 'hamlit/filters/base'
+
+module Hamlit
+  module Filters
+    class Tilt < Filters::Base
+      include Concerns::StringInterpolation
+
+      def self.render(name, source)
+        result = ::Tilt["t.#{name}"].new { source }.render
+        indent_source(result, indent_width: 2)
+      end
+
+      private
+
+      def compile_with_tilt(name, source, ast)
+        return runtime_compile(name, source, ast) if contains_interpolation?(source)
+
+        result  = [:static, Filters::Tilt.render(name, source)]
+        content = [:multi, [:static, "\n"], result]
+        ast << content
+      end
+
+      def runtime_compile(name, source, ast)
+        literal = string_literal(source)
+        code    = "::Hamlit::Filters::Tilt.render(#{name.inspect}, #{literal})"
+        content = [:multi, [:static, "\n"], [:dynamic, code]]
+        ast << content
+      end
+    end
+  end
+end

spec/hamlit/filters/sass_spec.rb

@@ -15,5 +15,23 @@ describe Hamlit::Filters::Sass do
         </style>
       HTML
     end
+
+    it 'renders sass filter with string interpolation' do
+      assert_render(<<-'HAML', <<-HTML)
+        - width = 1200
+        - height = 800
+        :sass
+          .users_controller
+            .show_action
+              width: #{width}px
+              height: #{height}px
+      HAML
+        <style>
+          .users_controller .show_action {
+            width: 1200px;
+            height: 800px; }
+        </style>
+      HTML
+    end
   end
 end