fix(typewriter): struct cannot extend structs

packages/@cdklabs/typewriter/src/renderer/typescript.ts

@@ -128,6 +128,12 @@ export class TypeScriptRenderer extends Renderer {
     this.renderDocs(structType, { forceStruct: true });
     this.emit(`${modifiers}interface ${structType.name}`);
     this.renderTypeParameters(structType.typeParameters);
+
+    if (structType.extends.length > 0) {
+      this.emit(' extends ');
+      this.emitList(structType.extends, ', ', (t) => this.renderType(t));
+    }
+
     this.emitBlock(' ', () => {
       const props = Array.from(structType.properties.values()).filter((p) => p.visibility === MemberVisibility.Public);
 

packages/@cdklabs/typewriter/src/struct.ts

@@ -36,6 +36,10 @@ export class StructType extends MemberType {
     spec.properties?.forEach((p) => this.addProperty(p));
   }
 
+  public get extends() {
+    return this.spec.extends ?? [];
+  }
+
   /**
    * Adds a property to the interface
    *

packages/@cdklabs/typewriter/test/interface.test.ts

@@ -1,4 +1,4 @@
-import { InterfaceType, Module, TypeScriptRenderer } from '../src';
+import { InterfaceType, Module, StructType, TypeScriptRenderer } from '../src';
 
 const renderer = new TypeScriptRenderer();
 let scope: Module;
@@ -24,3 +24,37 @@ test('can update some interface spec fields after initial creation', () => {
     }"
   `);
 });
+
+test('struct can extend struct', () => {
+  new StructType(scope, {
+    name: 'MyStruct',
+    extends: [scope.type('AnotherStruct')],
+  });
+
+  expect(renderer.render(scope)).toMatchInlineSnapshot(`
+    "/* eslint-disable prettier/prettier, @stylistic/max-len */
+    /**
+     * @struct
+     */
+    interface MyStruct extends AnotherStruct {
+
+    }"
+  `);
+});
+
+test('struct can extend multiple structs', () => {
+  new StructType(scope, {
+    name: 'MyStruct',
+    extends: [scope.type('AnotherStruct'), scope.type('SecondStruct')],
+  });
+
+  expect(renderer.render(scope)).toMatchInlineSnapshot(`
+    "/* eslint-disable prettier/prettier, @stylistic/max-len */
+    /**
+     * @struct
+     */
+    interface MyStruct extends AnotherStruct, SecondStruct {
+
+    }"
+  `);
+});