Added include_file to allow mixing in file-based templates

lib/smithy/liquid.rb

@@ -6,5 +6,6 @@
 require 'smithy/liquid/tags/asset'
 require 'smithy/liquid/tags/csrf'
 require 'smithy/liquid/tags/html'
+require 'smithy/liquid/tags/include_file'
 require 'smithy/liquid/tags/link'
 require 'smithy/liquid/tags/nav'

lib/smithy/liquid/tags/include_file.rb

@@ -0,0 +1,93 @@
+module Liquid
+
+  # IncludeFile allows templates to relate with other templates
+  #
+  # Simply include another template:
+  #
+  #   {% include_file 'product' %}
+  #
+  # IncludeFile a template with a local variable:
+  #
+  #   {% include_file 'product' with products[0] %}
+  #
+  # IncludeFile a template for a collection:
+  #
+  #   {% include_file 'product' for products %}
+  #
+  class IncludeFile < Tag
+    Syntax = /(#{QuotedFragment}+)(\s+(?:with|for)\s+(#{QuotedFragment}+))?/o
+
+    def initialize(tag_name, markup, tokens)
+      if markup =~ Syntax
+
+        @template_name = $1
+        @variable_name = $3
+        @attributes    = {}
+
+        markup.scan(TagAttributes) do |key, value|
+          @attributes[key] = value
+        end
+
+      else
+        raise SyntaxError.new("Error in tag 'include_file' - Valid syntax: include_file '[template]' (with|for) [object|collection]")
+      end
+
+      super
+    end
+
+    def parse(tokens)
+    end
+
+    def render(context)
+      partial = load_cached_partial(context)
+      variable = context[@variable_name || @template_name[1..-2]]
+
+      context.stack do
+        @attributes.each do |key, value|
+          context[key] = context[value]
+        end
+
+        if variable.is_a?(Array)
+          variable.collect do |var|
+            context[@template_name[1..-2]] = var
+            partial.render(context)
+          end
+        else
+          context[@template_name[1..-2]] = variable
+          partial.render(context)
+        end
+      end
+    end
+
+    private
+      def load_cached_partial(context)
+        cached_partials = context.registers[:cached_partials] || {}
+        template_name = context[@template_name]
+
+        if cached = cached_partials[template_name]
+          return cached
+        end
+        source = read_template_from_file_system(context)
+        partial = Liquid::Template.parse(source)
+        cached_partials[template_name] = partial
+        context.registers[:cached_partials] = cached_partials
+        partial
+      end
+
+      def read_template_from_file_system(context)
+        file_system = Liquid::Template.file_system
+
+        # make read_template_file call backwards-compatible.
+        case file_system.method(:read_template_file).arity
+        when 1
+          file_system.read_template_file(context[@template_name])
+        when 2
+          file_system.read_template_file(context[@template_name], context)
+        else
+          raise ArgumentError, "file_system.read_template_file expects two parameters: (template_name, context)"
+        end
+      end
+  end
+
+  Template.register_tag('include_file', IncludeFile)
+end