feat: supports enum schema

Author: zhufuyi

third_party/protoc-gen-openapiv2/options/annotations.proto

@@ -28,6 +28,13 @@ extend google.protobuf.MessageOptions {
   // different descriptor messages.
   Schema openapiv2_schema = 1042;
 }
+extend google.protobuf.EnumOptions {
+  // ID assigned by protobuf-global-extension-registry@google.com for gRPC-Gateway project.
+  //
+  // All IDs are the same, as assigned. It is okay that they are the same, as they extend
+  // different descriptor messages.
+  EnumSchema openapiv2_enum = 1042;
+}
 extend google.protobuf.ServiceOptions {
   // ID assigned by protobuf-global-extension-registry@google.com for gRPC-Gateway project.
   //

third_party/protoc-gen-openapiv2/options/openapiv2.proto

@@ -195,7 +195,7 @@ message Parameters {
 // `HeaderParameter` a HTTP header parameter.
 // See: https://swagger.io/specification/v2/#parameter-object
 message HeaderParameter {
-  // `Type` is a a supported HTTP header type.
+  // `Type` is a supported HTTP header type.
   // See https://swagger.io/specification/v2/#parameterType.
   enum Type {
     UNKNOWN = 0;
@@ -443,6 +443,45 @@ message Schema {
   string example = 6;
 }
 
+// `EnumSchema` is subset of fields from the OpenAPI v2 specification's Schema object.
+// Only fields that are applicable to Enums are included
+// See: https://github.com/OAI/OpenAPI-Specification/blob/3.0.0/versions/2.0.md#schemaObject
+//
+// Example:
+//
+//  option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_enum) = {
+//    ...
+//    title: "MyEnum";
+//    description:"This is my nice enum";
+//    example: "ZERO";
+//    required: true;
+//    ...
+//  };
+//
+message EnumSchema {
+  // A short description of the schema.
+  string description = 1;
+  string default = 2;
+  // The title of the schema.
+  string title = 3;
+  bool required = 4;
+  bool read_only = 5;
+  // Additional external documentation for this schema.
+  ExternalDocumentation external_docs = 6;
+  string example = 7;
+  // Ref is used to define an external reference to include in the message.
+  // This could be a fully qualified proto message reference, and that type must
+  // be imported into the protofile. If no message is identified, the Ref will
+  // be used verbatim in the output.
+  // For example:
+  //  `ref: ".google.protobuf.Timestamp"`.
+  string ref = 8;
+  // Custom properties that start with "x-" such as "x-foo" used to describe
+  // extra functionality that is not covered by the standard OpenAPI Specification.
+  // See: https://swagger.io/docs/specification/2-0/swagger-extensions/
+  map<string, google.protobuf.Value> extensions = 9;
+}
+
 // `JSONSchema` represents properties from JSON Schema taken, and as used, in
 // the OpenAPI v2 spec.
 //