Don't emit empty required property arrays

packages/openapi-generator/src/openapi.ts

@@ -44,7 +44,7 @@ function schemaToOpenAPI(
           },
           {} as Record<string, OpenAPIV3.SchemaObject | OpenAPIV3.ReferenceObject>,
         ),
-        required: schema.required,
+        ...(schema.required.length > 0 ? { required: schema.required } : {}),
       };
     case 'intersection':
       return {

packages/openapi-generator/test/openapi.test.ts

@@ -468,3 +468,73 @@ testCase('source file with a header comment', HEADER_COMMENT, {
     schemas: {},
   },
 });
+
+const EMPTY_REQUIRED = `
+import * as t from 'io-ts';
+import * as h from '@api-ts/io-ts-http';
+
+export const route = h.httpRoute({
+  path: '/foo',
+  method: 'GET',
+  request: h.httpRequest({
+    body: {
+      foo: t.string,
+    },
+  }),
+  response: {
+    /** foo response */
+    200: t.partial({ foo: t.string })
+  },
+});
+`;
+
+// Test that `required` is not emitted as an empty array
+testCase('object with no required properties', EMPTY_REQUIRED, {
+  openapi: '3.0.0',
+  info: {
+    title: 'Test',
+    version: '1.0.0',
+  },
+  paths: {
+    '/foo': {
+      get: {
+        parameters: [],
+        requestBody: {
+          content: {
+            'application/json': {
+              schema: {
+                type: 'object',
+                properties: {
+                  foo: {
+                    type: 'string',
+                  },
+                },
+                required: ['foo'],
+              },
+            },
+          },
+        },
+        responses: {
+          200: {
+            description: 'foo response',
+            content: {
+              'application/json': {
+                schema: {
+                  type: 'object',
+                  properties: {
+                    foo: {
+                      type: 'string',
+                    },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+  components: {
+    schemas: {},
+  },
+});