Only make deeply nested routes shallow when parent is shallow

Since `:shallow` may be set at any point in the resource nesting we should
only make the new and collection routes shallow when the parent is shallow.

This is a bit of a hack but until the mapper is refactored to an object graph
instead of a hash of merged values it's the best we can do.

Fixes #14684.

actionpack/CHANGELOG.md

@@ -1,9 +1,15 @@
+*   Only make deeply nested routes shallow when parent is shallow.
+
+    Fixes #14684.
+
+    *Andrew White*, *James Coglan*
+
 *   Append link to bad code to backtrace when exception is SyntaxError.
 
     *Boris Kuznetsov*
-    
+
 *   Swapped the parameters of assert_equal in `assert_select` so that the
-    proper values were printed correctly 
+    proper values were printed correctly
 
     Fixes #14422.
 

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -995,6 +995,7 @@ module ActionDispatch
             @as         = options[:as]
             @param      = (options[:param] || :id).to_sym
             @options    = options
+            @shallow    = false
           end
 
           def default_actions
@@ -1055,6 +1056,13 @@ module ActionDispatch
             "#{path}/:#{nested_param}"
           end
 
+          def shallow=(value)
+            @shallow = value
+          end
+
+          def shallow?
+            @shallow
+          end
         end
 
         class SingletonResource < Resource #:nodoc:
@@ -1361,7 +1369,7 @@ module ActionDispatch
           end
 
           with_scope_level(:nested) do
-            if shallow? && nesting_depth > 1
+            if shallow? && shallow_nesting_depth > 1
               shallow_scope(parent_resource.nested_scope, nested_options) { yield }
             else
               scope(parent_resource.nested_scope, nested_options) { yield }
@@ -1576,6 +1584,7 @@ module ActionDispatch
           end
 
           def resource_scope(kind, resource) #:nodoc:
+            resource.shallow = @scope[:shallow]
             old_resource, @scope[:scope_level_resource] = @scope[:scope_level_resource], resource
             @nesting.push(resource)
 
@@ -1600,6 +1609,10 @@ module ActionDispatch
             @nesting.size
           end
 
+          def shallow_nesting_depth #:nodoc:
+            @nesting.select(&:shallow?).size
+          end
+
           def param_constraint? #:nodoc:
             @scope[:constraints] && @scope[:constraints][parent_resource.param].is_a?(Regexp)
           end