3 files changed, 31 insertions, 1 deletions
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index dc627a4da4..bf608e162b 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,15 @@
+*   Unique the segment keys array for non-optimized url helpers
+
+    In Rails 3.2 you only needed pass an argument for dynamic segment once so
+    unique the segment keys array to match the number of args. Since the number
+    of args is less than required parts the non-optimized code path is selected.
+    This means to benefit from optimized url generation the arg needs to be
+    specified as many times as it appears in the path.
+
+    Fixes #12808
+
+    *Andrew White*
+
 *   Show full route constraints in error message
 
     When an optimized helper fails to generate, show the full route constraints
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index 10c8d748df..a03fb4cee7 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -220,7 +220,7 @@ module ActionDispatch
 
           def initialize(route, options)
             @options      = options
-            @segment_keys = route.segment_keys
+            @segment_keys = route.segment_keys.uniq
             @route        = route
           end
 
diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index d41b94511a..840c157642 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -2864,6 +2864,24 @@ class TestRoutingMapper < ActionDispatch::IntegrationTest
     assert !@request.params[:action].frozen?
   end
 
+  def test_multiple_positional_args_with_the_same_name
+    draw do
+      get '/downloads/:id/:id.tar' => 'downloads#show', as: :download, format: false
+    end
+
+    expected_params = {
+      controller: 'downloads',
+      action:     'show',
+      id:         '1'
+    }
+
+    get '/downloads/1/1.tar'
+    assert_equal 'downloads#show', @response.body
+    assert_equal expected_params, @request.symbolized_path_parameters
+    assert_equal '/downloads/1/1.tar', download_path('1')
+    assert_equal '/downloads/1/1.tar', download_path('1', '1')
+  end
+
 private
 
   def draw(&block)