8 files changed, 36 insertions, 27 deletions
diff --git a/actionpack/lib/abstract_controller/helpers.rb b/actionpack/lib/abstract_controller/helpers.rb
index df7382f02d..109eff10eb 100644
--- a/actionpack/lib/abstract_controller/helpers.rb
+++ b/actionpack/lib/abstract_controller/helpers.rb
@@ -184,7 +184,7 @@ module AbstractController
         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"
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 709e497a6d..3606d7e572 100644
--- a/activesupport/CHANGELOG.md
+++ b/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.
 
diff --git a/activesupport/lib/active_support/core_ext/load_error.rb b/activesupport/lib/active_support/core_ext/load_error.rb
index 768b980f21..d9fb392752 100644
--- a/activesupport/lib/active_support/core_ext/load_error.rb
+++ b/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 @@ class LoadError
   end
 end
 
-MissingSourceFile = LoadError
+MissingSourceFile = ActiveSupport::Deprecation::DeprecatedConstantProxy.new('MissingSourceFile', 'LoadError')
diff --git a/activesupport/lib/active_support/tagged_logging.rb b/activesupport/lib/active_support/tagged_logging.rb
index d5c2222d2e..9086a959aa 100644
--- a/activesupport/lib/active_support/tagged_logging.rb
+++ b/activesupport/lib/active_support/tagged_logging.rb
@@ -43,7 +43,9 @@ module ActiveSupport
       end
 
       def current_tags
-        Thread.current[:activesupport_tagged_logging_tags] ||= []
+        # We use our object ID here to void conflicting with other instances
+        thread_key = @thread_key ||= "activesupport_tagged_logging_tags:#{object_id}".freeze
+        Thread.current[thread_key] ||= []
       end
 
       private
diff --git a/activesupport/test/core_ext/load_error_test.rb b/activesupport/test/core_ext/load_error_test.rb
index 5f804c749b..b2a75a2bcc 100644
--- a/activesupport/test/core_ext/load_error_test.rb
+++ b/activesupport/test/core_ext/load_error_test.rb
@@ -1,26 +1,11 @@
 require 'abstract_unit'
 require 'active_support/core_ext/load_error'
 
-class TestMissingSourceFile < ActiveSupport::TestCase
-  def test_with_require
-    assert_raise(MissingSourceFile) { require 'no_this_file_don\'t_exist' }
-  end
-  def test_with_load
-    assert_raise(MissingSourceFile) { load 'nor_does_this_one' }
-  end
-  def test_path
-    begin load 'nor/this/one.rb'
-    rescue MissingSourceFile => e
-      assert_equal 'nor/this/one.rb', e.path
-    end
-  end
 
-  def test_is_missing
-    begin load 'nor_does_this_one'
-    rescue MissingSourceFile => e
-      assert e.is_missing?('nor_does_this_one')
-      assert e.is_missing?('nor_does_this_one.rb')
-      assert_not e.is_missing?('some_other_file')
+class TestMissingSourceFile < ActiveSupport::TestCase
+  def test_it_is_deprecated
+    assert_deprecated do
+      MissingSourceFile.new
     end
   end
 end
diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index 96e9bd1e65..d780acf5f9 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -72,7 +72,7 @@ class DependenciesTest < ActiveSupport::TestCase
   end
 
   def test_missing_dependency_raises_missing_source_file
-    assert_raise(MissingSourceFile) { require_dependency("missing_service") }
+    assert_raise(LoadError) { require_dependency("missing_service") }
   end
 
   def test_dependency_which_raises_exception_isnt_added_to_loaded_set
@@ -613,7 +613,7 @@ class DependenciesTest < ActiveSupport::TestCase
 
   def test_nested_load_error_isnt_rescued
     with_loading 'dependencies' do
-      assert_raise(MissingSourceFile) do
+      assert_raise(LoadError) do
         RequiresNonexistent1
       end
     end
diff --git a/activesupport/test/tagged_logging_test.rb b/activesupport/test/tagged_logging_test.rb
index 27f629474e..03a63e94e8 100644
--- a/activesupport/test/tagged_logging_test.rb
+++ b/activesupport/test/tagged_logging_test.rb
@@ -79,6 +79,19 @@ class TaggedLoggingTest < ActiveSupport::TestCase
     assert_equal "[OMG] Cool story bro\n[BCX] Funky time\n", @output.string
   end
 
+  test "keeps each tag in their own instance" do
+    @other_output = StringIO.new
+    @other_logger = ActiveSupport::TaggedLogging.new(MyLogger.new(@other_output))
+    @logger.tagged("OMG") do
+      @other_logger.tagged("BCX") do
+        @logger.info "Cool story bro"
+        @other_logger.info "Funky time"
+      end
+    end
+    assert_equal "[OMG] Cool story bro\n", @output.string
+    assert_equal "[BCX] Funky time\n", @other_output.string
+  end
+
   test "cleans up the taggings on flush" do
     @logger.tagged("BCX") do
       Thread.new do
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index c857f30541..ba839e1723 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/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"