5 files changed, 38 insertions, 7 deletions
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index be44f61ea7..bce5855c4a 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -45,18 +45,26 @@ module Dependencies #:nodoc:
       # Append .rb if we have a bare file name.
       load_file_name = (file_name =~ /\.rb$/ ? file_name : "#{file_name}.rb")
 
-      # Enable warnings iff this file has not been loaded before.
-      if history.include?(file_name)
-        load load_file_name
-      else
-        enable_warnings { load load_file_name }
+      # Record that we've seen this file *before* loading it to avoid an
+      # infinite loop with mutual dependencies.
+      loaded << file_name
+
+      begin
+        # Enable warnings iff this file has not been loaded before.
+        if history.include?(file_name)
+          load load_file_name
+        else
+          enable_warnings { load load_file_name }
+        end
+      rescue
+        loaded.delete file_name
+        raise
       end
     else
       require file_name
     end
 
-    # Record that we've seen this file.
-    loaded  << file_name
+    # Record history *after* loading so first load gets warnings.
     history << file_name
   end
 
diff --git a/activesupport/test/dependencies/mutual_one.rb b/activesupport/test/dependencies/mutual_one.rb
new file mode 100644
index 0000000000..eb5e056efb
--- /dev/null
+++ b/activesupport/test/dependencies/mutual_one.rb
@@ -0,0 +1,2 @@
+$mutual_dependencies_count += 1
+require_dependency 'mutual_two'
diff --git a/activesupport/test/dependencies/mutual_two.rb b/activesupport/test/dependencies/mutual_two.rb
new file mode 100644
index 0000000000..99ba337e55
--- /dev/null
+++ b/activesupport/test/dependencies/mutual_two.rb
@@ -0,0 +1,2 @@
+$mutual_dependencies_count += 1
+require_dependency 'mutual_one'
diff --git a/activesupport/test/dependencies/raises_exception.rb b/activesupport/test/dependencies/raises_exception.rb
index df8d8b79d0..69750eee72 100644
--- a/activesupport/test/dependencies/raises_exception.rb
+++ b/activesupport/test/dependencies/raises_exception.rb
@@ -1,2 +1,3 @@
 $raises_exception_load_count += 1
 raise 'Loading me failed, so do not add to loaded or history.'
+$raises_exception_load_count += 1
diff --git a/activesupport/test/dependencies_test.rb b/activesupport/test/dependencies_test.rb
index a59b0284a9..b801ce6cf0 100644
--- a/activesupport/test/dependencies_test.rb
+++ b/activesupport/test/dependencies_test.rb
@@ -79,4 +79,22 @@ class DependenciesTest < Test::Unit::TestCase
   ensure
     Dependencies.mechanism = old_mechanism
   end
+
+  def test_mutual_dependencies_dont_infinite_loop
+    $LOAD_PATH.unshift "#{File.dirname(__FILE__)}/dependencies"
+    old_mechanism, Dependencies.mechanism = Dependencies.mechanism, :load
+
+    $mutual_dependencies_count = 0
+    assert_nothing_raised { require_dependency 'mutual_one' }
+    assert_equal 2, $mutual_dependencies_count
+
+    Dependencies.clear
+
+    $mutual_dependencies_count = 0
+    assert_nothing_raised { require_dependency 'mutual_two' }
+    assert_equal 2, $mutual_dependencies_count
+  ensure
+    $LOAD_PATH.shift
+    Dependencies.mechanism = old_mechanism
+  end
 end