Speed up development by only reloading classes if dependencies files changed.

This can be turned off by setting `config.reload_classes_only_on_change` to false.

Extensions like Active Record should add their respective files like db/schema.rb and db/structure.sql to `config.watchable_files` if they want their changes to affect classes reloading.

Thanks to https://github.com/paneq/active_reload and Pastorino for the inspiration. <3

3 files changed, 48 insertions, 11 deletions

diff --git a/activesupport/lib/active_support/file_update_checker.rb b/activesupport/lib/active_support/file_update_checker.rb
index 77bc5388d6..4137bbf6a0 100644
--- a/activesupport/lib/active_support/file_update_checker.rb
+++ b/activesupport/lib/active_support/file_update_checker.rb
@@ -39,30 +39,53 @@ module ActiveSupport
       @paths = paths
       @glob  = compile_glob(@paths.extract_options!)
       @block = block
+      @updated_at = nil
       @last_update_at = calculate ? updated_at : nil
     end
 
-    def updated_at
-      all = []
-      all.concat @paths
-      all.concat Dir[@glob] if @glob
-      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 compile_glob(hash)
+    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|
@@ -71,7 +94,7 @@ module ActiveSupport
       "{#{globs.join(",")}}"
     end
 
-    def compile_ext(array)
+    def compile_ext(array) #:nodoc:
       array = Array.wrap(array)
       return if array.empty?
       ".{#{array.join(",")}}"
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
diff --git a/activesupport/test/file_update_checker_test.rb b/activesupport/test/file_update_checker_test.rb
index a5a9b7a682..52c1f3260d 100644
--- a/activesupport/test/file_update_checker_test.rb
+++ b/activesupport/test/file_update_checker_test.rb
@@ -54,6 +54,19 @@ class FileUpdateCheckerWithEnumerableTest < Test::Unit::TestCase
     assert_equal 1, i
   end
 
+  def test_should_cache_updated_result_until_flushed
+    i = 0
+    checker = ActiveSupport::FileUpdateChecker.new(FILES, true){ i += 1 }
+    assert !checker.updated?
+
+    sleep(1)
+    FileUtils.touch(FILES)
+
+    assert checker.updated?
+    assert checker.execute_if_updated
+    assert !checker.updated?
+  end
+
   def test_should_invoke_the_block_if_a_watched_dir_changed_its_glob
     i = 0
     checker = ActiveSupport::FileUpdateChecker.new([{"tmp_watcher" => [:txt]}], true){ i += 1 }