Version specific allow_extensions for Discriminator

A change in OpenAPI 3.1 is that the Discriminator object can accept
extensions, when previously this was not allowed.

In order to code this I've had to adjust the DSL so that the
allow_extensions method can accept a block.

We didn't have unit tests for the DSL so I'm only testing this at the
node level. This should be ok as it has full coverage.

TODO.md

@@ -57,7 +57,7 @@ For OpenAPI 3.1
 - [ ] Callbacks can now reference a PathItem - previously required them
 - [ ] Check out whether pathItem references match the rules for relative resolution
 - [ ] Parameter object can have space delimited or pipeDelimited styles
-- [ ] Discriminator object can be extended
+- [x] Discriminator object can be extended
 - [x] mutualTLS as a security scheme
 - [ ] I think strictness of Security Requirement rules has changed
 

lib/openapi3_parser/node_factory/discriminator.rb

@@ -5,6 +5,8 @@
 module Openapi3Parser
   module NodeFactory
     class Discriminator < NodeFactory::Object
+      allow_extensions { |context| context.openapi_version >= "3.1" }
+
       field "propertyName", input_type: String, required: true
       field "mapping", input_type: Hash,
                        validate: :validate_mapping,

lib/openapi3_parser/node_factory/object.rb

@@ -12,6 +12,7 @@ class Object
       def_delegators "self.class",
                      :field_configs,
                      :extension_regex,
+                     :allowed_extensions?,
                      :mutually_exclusive_fields,
                      :allowed_default?,
                      :validations

lib/openapi3_parser/node_factory/object_factory/dsl.rb

@@ -17,8 +17,21 @@ def field_configs
           @field_configs ||= {}
         end
 
-        def allow_extensions(regex: EXTENSION_REGEX)
+        def allow_extensions(regex: EXTENSION_REGEX, &block)
           @extension_regex = regex
+          @allowed_extensions = block || true
+        end
+
+        def allowed_extensions?(context)
+          @allowed_extensions ||= nil
+
+          allowed = if @allowed_extensions.respond_to?(:call)
+                      @allowed_extensions.call(context)
+                    else
+                      @allowed_extensions
+                    end
+
+          !!allowed
         end
 
         def extension_regex

lib/openapi3_parser/node_factory/object_factory/validator.rb

@@ -39,9 +39,11 @@ def check_required_fields
         end
 
         def check_unexpected_fields
+          extension_regex = factory.extension_regex if factory.allowed_extensions?(validatable.context)
+
           Validators::UnexpectedFields.call(
             validatable,
-            extension_regex: factory.extension_regex,
+            extension_regex: extension_regex,
             allowed_fields: factory.allowed_fields,
             raise_on_invalid: raise_on_invalid
           )

spec/lib/openapi3_parser/node_factory/discriminator_spec.rb

@@ -9,4 +9,32 @@
       }
     end
   end
+
+  describe "allow extensions" do
+    it "accepts extensions for OpenAPI 3.1" do
+      factory_context = create_node_factory_context(
+        {
+          "propertyName" => "test",
+          "x-extension" => "value"
+        },
+        document_input: { "openapi" => "3.1.0" }
+      )
+
+      instance = described_class.new(factory_context)
+      expect(instance).to be_valid
+    end
+
+    it "rejects extensions for OpenAPI < 3.1" do
+      factory_context = create_node_factory_context(
+        {
+          "propertyName" => "test",
+          "x-extension" => "value"
+        },
+        document_input: { "openapi" => "3.0.0" }
+      )
+
+      instance = described_class.new(factory_context)
+      expect(instance).not_to be_valid
+    end
+  end
 end