Deprecate MissingSourceFile in favor of LoadError.

`MissingSourceFile` was just an alias to `LoadError` and was not
being raised inside the framework.

Author: rafaelfranca

activesupport/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Deprecate `MissingSourceFile` in favor of `LoadError`.
+
+    `MissingSourceFile` was just an alias to `LoadError` and was not being
+    raised inside the framework.
+
+    *Rafael Mendonça França*
+
 *   Add support for error dispatcher classes in `ActiveSupport::Rescuable`.
     Now it acts closer to Ruby's rescue.
 

activesupport/lib/active_support/core_ext/load_error.rb

@@ -1,3 +1,5 @@
+require 'active_support/deprecation/proxy_wrappers'
+
 class LoadError
   REGEXPS = [
     /^no such file to load -- (.+)$/i,
@@ -25,4 +27,4 @@ def is_missing?(location)
   end
 end
 
-MissingSourceFile = LoadError
+MissingSourceFile = ActiveSupport::Deprecation::DeprecatedConstantProxy.new('MissingSourceFile', 'LoadError')

activesupport/test/core_ext/load_error_test.rb

@@ -1,6 +1,15 @@
 require 'abstract_unit'
 require 'active_support/core_ext/load_error'
 
+
+class TestMissingSourceFile < ActiveSupport::TestCase
+  def test_it_is_deprecated
+    assert_deprecated do
+      MissingSourceFile.new
+    end
+  end
+end
+
 class TestLoadError < ActiveSupport::TestCase
   def test_with_require
     assert_raise(LoadError) { require 'no_this_file_don\'t_exist' }

guides/source/active_support_core_extensions.md

@@ -3873,7 +3873,7 @@ def default_helper_module!
   module_name = name.sub(/Controller$/, '')
   module_path = module_name.underscore
   helper module_path
-rescue MissingSourceFile => e
+rescue LoadError => e
   raise e unless e.is_missing? "helpers/#{module_path}_helper"
 rescue NameError => e
   raise e unless e.missing_name? "#{module_name}Helper"
@@ -3885,7 +3885,7 @@ NOTE: Defined in `active_support/core_ext/name_error.rb`.
 Extensions to `LoadError`
 -------------------------
 
-Active Support adds `is_missing?` to `LoadError`, and also assigns that class to the constant `MissingSourceFile` for backwards compatibility.
+Active Support adds `is_missing?` to `LoadError`.
 
 Given a path name `is_missing?` tests whether the exception was raised due to that particular file (except perhaps for the ".rb" extension).
 
@@ -3896,7 +3896,7 @@ def default_helper_module!
   module_name = name.sub(/Controller$/, '')
   module_path = module_name.underscore
   helper module_path
-rescue MissingSourceFile => e
+rescue LoadError => e
   raise e unless e.is_missing? "helpers/#{module_path}_helper"
 rescue NameError => e
   raise e unless e.missing_name? "#{module_name}Helper"