context.rb in sprockets-4.0.0.beta4

- old
+ new

@@ -16,10 +16,28 @@
   #     <%= asset_url "foo.png" %>
   #
   # The `Context` also collects dependencies declared by
   # assets. See `DirectiveProcessor` for an example of this.
   class Context
+    # Internal: Proxy for ENV that keeps track of the environment variables used
+    class ENVProxy < SimpleDelegator
+      def initialize(context)
+        @context = context
+        super(ENV)
+      end
+
+      def [](key)
+        @context.depend_on_env(key)
+        super
+      end
+
+      def fetch(key, *)
+        @context.depend_on_env(key)
+        super
+      end
+    end
+
     attr_reader :environment, :filename
 
     def initialize(input)
       @environment  = input[:environment]
       @metadata     = input[:metadata]
@@ -40,10 +58,14 @@
         stubbed: @stubbed,
         links: @links,
         dependencies: @dependencies }
     end
 
+    def env_proxy
+      ENVProxy.new(self)
+    end
+
     # Returns the environment path that contains the file.
     #
     # If `app/javascripts` and `app/stylesheets` are in your path, and
     # current file is `app/javascripts/foo/bar.js`, `load_path` would
     # return `app/javascripts`.
@@ -118,9 +140,18 @@
     # invalidate the dependency asset will invalidate the source
     # file. Unlike `depend_on`, this will recursively include
     # the target asset's dependencies.
     def depend_on_asset(path)
       load(resolve(path))
+    end
+
+    # `depend_on_env` allows you to state a dependency on an environment
+    # variable.
+    #
+    # This is used for caching purposes. Any changes in the value of the
+    # environment variable will invalidate the cache of the source file.
+    def depend_on_env(key)
+      @dependencies << "env:#{key}"
     end
 
     # `require_asset` declares `path` as a dependency of the file. The
     # dependency will be inserted before the file and will only be
     # included once.