fix: flattened optional type is optional

Author: sebws

packages/rtk-query-codegen-openapi/src/generate.ts

@@ -324,7 +324,6 @@ export async function generateApi(
     const queryArgValues = Object.values(queryArg);
 
     const isFlatArg = flattenArg && queryArgValues.length === 1;
-
     const QueryArg = factory.createTypeReferenceNode(
       registerInterface(
         factory.createTypeAliasDeclaration(
@@ -333,7 +332,16 @@ export async function generateApi(
           undefined,
           queryArgValues.length > 0
             ? isFlatArg
-              ? withQueryComment({ ...queryArgValues[0].type }, queryArgValues[0], false)
+              ? withQueryComment(
+                  factory.createUnionTypeNode([
+                    queryArgValues[0].type,
+                    ...(!queryArgValues[0].required
+                      ? [factory.createKeywordTypeNode(ts.SyntaxKind.UndefinedKeyword)]
+                      : []),
+                  ]),
+                  queryArgValues[0],
+                  false
+                )
               : factory.createTypeLiteralNode(
                   queryArgValues.map((def) =>
                     withQueryComment(

packages/rtk-query-codegen-openapi/test/generateEndpoints.test.ts

@@ -113,6 +113,22 @@ describe('option flattenArg', () => {
     });
     expect(api).toContain('queryArg.body');
   });
+
+  it('should flatten an optional arg as an optional type', async () => {
+    const api = await generateEndpoints({
+      ...config,
+      filterEndpoints: 'findPetsByTags',
+    });
+    expect(api).toMatch(/\| undefined/);
+  });
+
+  it('should not flatten a non-optional arg with a superfluous union', async () => {
+    const api = await generateEndpoints({
+      ...config,
+      filterEndpoints: 'getPetById',
+    });
+    expect(api).not.toMatch(/^\s*\|/);
+  });
 });
 
 test('hooks generation', async () => {