2 files changed, 74 insertions, 8 deletions

diff --git a/activesupport/lib/active_support/file_update_checker.rb b/activesupport/lib/active_support/file_update_checker.rb
index 9d617b39d4..4137bbf6a0 100644
--- a/activesupport/lib/active_support/file_update_checker.rb
+++ b/activesupport/lib/active_support/file_update_checker.rb
@@ -1,3 +1,6 @@
+require "active_support/core_ext/array/wrap"
+require "active_support/core_ext/array/extract_options"
+
 module ActiveSupport
   # This class is responsible to track files and invoke the given block
   # whenever one of these files are changed. For example, this class
@@ -15,24 +18,86 @@ module ActiveSupport
   class FileUpdateChecker
     attr_reader :paths, :last_update_at
 
+    # It accepts two parameters on initialization. The first is
+    # the *paths* and the second is *calculate*, a boolean.
+    #
+    # paths must be an array of file paths but can contain a hash as
+    # last argument. The hash must have directories as keys and the
+    # value is an array of extensions to be watched under that directory.
+    #
+    # If *calculate* is true, the latest updated at will calculated
+    # on initialization, therefore, the first call to execute_if_updated
+    # will only evaluate the block if something really changed.
+    #
+    # This method must also receive a block that will be the block called
+    # once a file changes.
+    #
+    # This particular implementation checks for added files and updated files,
+    # but not removed files. Directories lookup are compiled to a glob for
+    # performance.
     def initialize(paths, calculate=false, &block)
       @paths = paths
+      @glob  = compile_glob(@paths.extract_options!)
       @block = block
+      @updated_at = nil
       @last_update_at = calculate ? updated_at : nil
     end
 
-    def updated_at
-      # TODO: Use Enumerable check once we get rid of 1.8.7
-      all = paths.is_a?(Array) ? paths : Dir[paths]
-      all.map { |path| File.mtime(path) }.max
+    # Check if any of the entries were updated. If so, the updated_at
+    # value is cached until flush! is called.
+    def updated?
+      current_updated_at = updated_at
+      if @last_update_at != current_updated_at
+        @updated_at = updated_at
+        true
+      else
+        false
+      end
+    end
+
+    # Flush the cache so updated? is calculated again
+    def flush!
+      @updated_at = nil
     end
 
+    # Execute the block given if updated. This call
+    # always flush the cache.
     def execute_if_updated
-      current_update_at = self.updated_at
-      if @last_update_at != current_update_at
-        @last_update_at = current_update_at
+      if updated?
+        @last_update_at = updated_at
         @block.call
+        true
+      else
+        false
       end
+    ensure
+      flush!
+    end
+
+    private
+
+    def updated_at #:nodoc:
+      @updated_at || begin
+        all = []
+        all.concat @paths
+        all.concat Dir[@glob] if @glob
+        all.map { |path| File.mtime(path) }.max
+      end
+    end
+
+    def compile_glob(hash) #:nodoc:
+      return if hash.empty?
+      globs = []
+      hash.each do |key, value|
+        globs << "#{key}/**/*#{compile_ext(value)}"
+      end
+      "{#{globs.join(",")}}"
+    end
+
+    def compile_ext(array) #:nodoc:
+      array = Array.wrap(array)
+      return if array.empty?
+      ".{#{array.join(",")}}"
     end
   end
 end
diff --git a/activesupport/lib/active_support/i18n_railtie.rb b/activesupport/lib/active_support/i18n_railtie.rb
index 4c59fe9ac9..a989ff8f57 100644
--- a/activesupport/lib/active_support/i18n_railtie.rb
+++ b/activesupport/lib/active_support/i18n_railtie.rb
@@ -17,7 +17,8 @@ module I18n
     # point, no path was added to the reloader, I18n.reload! is not triggered
     # on to_prepare callbacks. This will only happen on the config.after_initialize
     # callback below.
-    initializer "i18n.callbacks" do
+    initializer "i18n.callbacks" do |app|
+      app.reloaders << I18n::Railtie.reloader
       ActionDispatch::Reloader.to_prepare do
         I18n::Railtie.reloader.execute_if_updated
       end