504 - Fix additionalProperties on object type (#523)

As stated in the documentation:
https://swagger.io/docs/specification/data-models/dictionaries/
Freeform objects (objects with any value) can be defined by setting
additionalProperties either to true or {}. Previously:
foo?: { [key: string]: { [key: string]: any } }
was the output instead of:
foo?: { [key: string]: any }
This is fixed and tested with this PR.

Co-authored-by: fabio.wanner <fabio.wanner@m-f.ch>

Author: FabioWanner

src/transform/schema.ts

@@ -94,7 +94,7 @@ export function transformSchemaObj(node: any): string {
       // if additional properties, add an intersection with a generic map type
       let additionalProperties: string | undefined;
       if (node.additionalProperties) {
-        if (node.additionalProperties === true) {
+        if (node.additionalProperties === true || Object.keys(node.additionalProperties).length === 0) {
           additionalProperties = `{ [key: string]: any }`;
         } else if (typeof node.additionalProperties === "object") {
           const oneOf: any[] | undefined = (node.additionalProperties as any).oneOf || undefined; // TypeScript does a really bad job at inference here, so we enforce a type

tests/schema.test.ts

@@ -163,6 +163,9 @@ describe("SchemaObject", () => {
       // boolean
       expect(transform({ additionalProperties: true })).toBe(`{ [key: string]: any }`);
 
+      // empty object
+      expect(transform({ additionalProperties: {} })).toBe(`{ [key: string]: any }`);
+
       // type
       expect(transform({ additionalProperties: { type: "string" } })).toBe(`{ [key: string]: string; }`);