Merge pull request #21804 from merhard/mounted_engine_route_fix

Mounted engine route fix

3 files changed, 15 insertions, 2 deletions

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index a0a12f1b0e..a50b81b439 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   Fix regression in mounted engine named routes generation for app deployed to
+    a subdirectory. `relative_url_root` was prepended to the path twice (e.g.
+    "/subdir/subdir/engine_path" instead of "/subdir/engine_path")
+
+    Fixes #20920. Fixes #21459.
+
+    *Matthew Erhard*
+
 *   ActionDispatch::Response#new no longer applies default headers.  If you want
     default headers applied to the response object, then call
     `ActionDispatch::Response.create`.  This change only impacts people who are
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index cfd50f616d..2f1c2afb91 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -665,6 +665,7 @@ module ActionDispatch
                   super(options)
                 else
                   prefix_options = options.slice(*_route.segment_keys)
+                  prefix_options[:relative_url_root] = ''.freeze
                   # we must actually delete prefix segment keys to avoid passing them to next url_for
                   _route.segment_keys.each { |k| options.delete(k) }
                   _routes.url_helpers.send("#{name}_path", prefix_options)
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index e4b8d5993e..339e2b7c4a 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -656,14 +656,18 @@ module ActionDispatch
 
       RESERVED_OPTIONS = [:host, :protocol, :port, :subdomain, :domain, :tld_length,
                           :trailing_slash, :anchor, :params, :only_path, :script_name,
-                          :original_script_name]
+                          :original_script_name, :relative_url_root]
 
       def optimize_routes_generation?
         default_url_options.empty?
       end
 
       def find_script_name(options)
-        options.delete(:script_name) || relative_url_root || ''
+        options.delete(:script_name) || find_relative_url_root(options) || ''
+      end
+
+      def find_relative_url_root(options)
+        options.delete(:relative_url_root) || relative_url_root
       end
 
       def path_for(options, route_name = nil)