Add identifier, as a mutually exclusive field, to License

This adds the identifier field to License - as outlined in the OpenAPI
3.1 Specification [1].

A couple of things I considered doing for this, but ultimately didn't
do, were:

- Determine whether the SPDX license expression format could be
  validated with a regex. It looked like it probably could but not sure
  if we want to be that strict.
- Add a hook in that would allow us to decide which OpenAPI versions
  would use the mutually_exclusive DSL method. I decided this wasn't
  necessary for now since the only benefit seems to be a slightly nicer
  error message.

Author: kevindew

TODO.md

@@ -51,7 +51,7 @@ For OpenAPI 3.1
 - [ ] Create a maxi OpenAPI 3.1 integration test to collate all the known changes
 - [ ] jsonSchemaDialect should default to OAS one
 - [x] Allow summary and description in Reference objects
-- [ ] Add identifier to License node, make mutually exclusive with URL
+- [x] Add identifier to License node, make mutually exclusive with URL
 - [ ] ServerVariable enum must not be empty
 - [ ] Add pathItems to components
 - [ ] Callbacks can now reference a PathItem - previously required them

lib/openapi3_parser/node/license.rb

@@ -11,6 +11,11 @@ def name
         self["name"]
       end
 
+      # @return [String, nil]
+      def identifier
+        self["identifier"]
+      end
+
       # @return [String, nil]
       def url
         self["url"]

lib/openapi3_parser/node_factory/license.rb

@@ -9,9 +9,13 @@ module NodeFactory
     class License < NodeFactory::Object
       allow_extensions
       field "name", input_type: String, required: true
+      field "identifier",
+            input_type: String,
+            allowed: ->(context) { context.openapi_version >= "3.1" }
       field "url",
             input_type: String,
             validate: Validation::InputValidator.new(Validators::Url)
+      mutually_exclusive "identifier", "url"
 
       def build_node(data, node_context)
         Node::License.new(data, node_context)

spec/lib/openapi3_parser/node_factory/license_spec.rb

@@ -24,4 +24,39 @@
       expect(instance).to have_validation_error("#/url")
     end
   end
+
+  describe "identifier field" do
+    it "accepts an identifier field for OpenAPI >= v3.1" do
+      factory_context = create_node_factory_context(
+        minimal_license_definition.merge({ "identifier" => "Apache-2.0" }),
+        document_input: { "openapi" => "3.1.0" }
+      )
+      expect(described_class.new(factory_context)).to be_valid
+    end
+
+    it "rejects an identifier field for OpenAPI < v3.1" do
+      factory_context = create_node_factory_context(
+        minimal_license_definition.merge({ "identifier" => "Apache-2.0" }),
+        document_input: { "openapi" => "3.0.0" }
+      )
+      instance = described_class.new(factory_context)
+
+      expect(instance).not_to be_valid
+      expect(instance).to have_validation_error("#/").with_message("Unexpected fields: identifier")
+    end
+
+    it "rejects both a license and a url field (mutually exclusive)" do
+      factory_context = create_node_factory_context(
+        minimal_license_definition.merge({
+                                           "identifier" => "Apache-2.0",
+                                           "url" => "https://example.com/url"
+                                         }),
+        document_input: { "openapi" => "3.1.0" }
+      )
+      instance = described_class.new(factory_context)
+
+      expect(instance).not_to be_valid
+      expect(instance).to have_validation_error("#/").with_message("identifier and url are mutually exclusive fields")
+    end
+  end
 end