fix type definition for fastify.swagger({ yaml: true }) (#670)

Author: dwickern

index.d.ts

@@ -20,11 +20,10 @@ declare module 'openapi-types' {
 
 declare module 'fastify' {
   interface FastifyInstance {
-    swagger: (
-      opts?: {
-        yaml?: boolean;
-      }
-    ) => OpenAPI.Document;
+    swagger:
+      ((opts?: { yaml?: false }) => OpenAPI.Document) &
+      ((opts: { yaml: true }) => string) &
+      ((opts: { yaml: boolean }) => OpenAPI.Document | string);
 
     swaggerCSP: {
       script: string[];

test/types/types.test.ts

@@ -6,6 +6,8 @@ import fastifySwagger, {
   FastifySwaggerUiHooksOptions, JSONObject,
 } from "../.."
 import { minimalOpenApiV3Document } from './minimal-openapiV3-document';
+import { expectType } from "tsd";
+import { OpenAPI } from "openapi-types";
 
 const app = fastify();
 const uiConfig: FastifySwaggerUiConfigOptions = {
@@ -227,3 +229,8 @@ app.register(fastifySwagger, {
 .ready((err) => {
   app.swagger();
 })
+
+expectType<OpenAPI.Document>(app.swagger())
+expectType<OpenAPI.Document>(app.swagger({ yaml: false }))
+expectType<string>(app.swagger({ yaml: true }))
+expectType<OpenAPI.Document | string>(app.swagger({ yaml: Boolean(process.env.YAML) }))