cause rails to correctly place optional path parameters

previously, if you specify a url parameter that is part of the path as false it would include that part of the path as parameter at the end of the url instead of in the path for example:
`get "(/optional/:optional_id)/things" => "foo#foo", as: :things`
`things_path(optional_id: false)  # => /things?optional_id=false`

this is not the case for empty string,
`things_path(optional_id: '')  # => "/things"

this is due to a quark in how path parameters get removed from the parameters.

we where doing `(paramter || recall).nil?` which returns nil if both values are nil however it also return nil if one value is false and the other value is nil. i.e. `(false || nil).nil # => nil` which is confusing.

After this change, `true` and `false` will be treated the same when used as optional path parameters. meaning now,

```
get '(this/:my_bool)/that' as: :that

that_path(my_bool: true) # => `/this/true/that`
that_path(my_bool: false) # => `/this/false/that`
```
fixes: #42280

Co-authored-by: Ryuta Kamizono <kamipo@gmail.com>

actionpack/lib/action_dispatch/journey/formatter.rb

@@ -103,7 +103,7 @@ def extract_parameterized_parts(route, options, recall)
           parameterized_parts = recall.merge(options)
 
           keys_to_keep = route.parts.reverse_each.drop_while { |part|
-            !(options.key?(part) || route.scope_options.key?(part)) || (options[part] || recall[part]).nil?
+            !(options.key?(part) || route.scope_options.key?(part)) || (options[part].nil? && recall[part].nil?)
           } | route.required_parts
 
           parameterized_parts.delete_if do |bad_key, _|
@@ -118,7 +118,7 @@ def extract_parameterized_parts(route, options, recall)
             end
           end
 
-          parameterized_parts.keep_if { |_, v| v }
+          parameterized_parts.compact!
           parameterized_parts
         end
 

actionpack/lib/action_dispatch/journey/visitors.rb

@@ -40,7 +40,7 @@ def evaluate(hash)
         @parameters.each do |index|
           param = parts[index]
           value = hash[param.name]
-          return "" unless value
+          return "" if value.nil?
           parts[index] = param.escape value
         end
 

actionpack/test/dispatch/url_generation_test.rb

@@ -16,6 +16,7 @@ def index
 
     Routes.draw do
       get "/foo", to: "my_route_generating#index", as: :foo
+      get "(/optional/:optional_id)/baz", to: "my_route_generating#index", as: :baz
 
       resources :bars
 
@@ -127,6 +128,34 @@ def app
       assert_equal "http://example.com/foo", foo_url(subdomain: "")
     end
 
+    test "keep optional path parameter when given" do
+      assert_equal "http://www.example.com/optional/123/baz", baz_url(optional_id: 123)
+    end
+
+    test "keep optional path parameter when true" do
+      assert_equal "http://www.example.com/optional/true/baz", baz_url(optional_id: true)
+    end
+
+    test "omit optional path parameter when false" do
+      assert_equal "http://www.example.com/optional/false/baz", baz_url(optional_id: false)
+    end
+
+    test "omit optional path parameter when blank" do
+      assert_equal "http://www.example.com/baz", baz_url(optional_id: "")
+    end
+
+    test "keep positional path parameter when true" do
+      assert_equal "http://www.example.com/optional/true/baz", baz_url(true)
+    end
+
+    test "omit positional path parameter when false" do
+      assert_equal "http://www.example.com/optional/false/baz", baz_url(false)
+    end
+
+    test "omit positional path parameter when blank" do
+      assert_equal "http://www.example.com/baz", baz_url("")
+    end
+
     test "generating URLs with trailing slashes" do
       assert_equal "/bars.json", bars_path(
         trailing_slash: true,